Mars

We have found that a rather simple thermal model of the Martian surface, in combination with current observations of the atmospheric composition, points strongly toward the conclusion that the polar caps of Mars consist almost entirely of frozen CO(2). This study was based upon the following principal assumptions. 1) Carbon dioxide is a major constituent of the Martian atmosphere. 2) The blanketing effect of the atmosphere is small, and due principally to the absorption band of CO(2) near 15 microns. 3) Lateral and convective heat transfer by the atmosphere is negligible. 4) The far-infrared emissivity of the Martian soil and of solid CO(2) are near unity. 5) The reflectivities of the soil and of solid CO(2) in the visible part of the spectrum are about 0.15 and 0.65, respectively. 6) Values for soil conductivity, density, and specific heat are those characteristic of powdered minerals at low gas pressure. 7) Water is a minor constituent of the Martian atmosphere, the maximum total amount in the atmosphere being 10 to 30 X 1O(-4) g cm(-2). In addition, several simplifications were made, which might have significant effects but should not alter our principal conclusions. Among these are the following. 1) Local blanketing or snowfall effects due to clouds or polar haze were ignored. 2) Dark and light areas were not differentiated in this study, although Sinton and Strong (6) have observed temperature differences between such areas. 3) The effects of local topography and microrelief were neglected. We believe that these must have quite significant effects at the higher latitudes, especially in connection with the evaporation of the remanent south polar cap. 4) Variation of reflectivity with angle of incidence of the sunlight was neglected. 5) Temperature dependence of soil conductivity and specific heat was ignored. 6) Effects of saturation of the soil by ice upon the thermal properties of the soil were neglected. Although in our main investigation we used certain specific values for the various relevant parameters, we also tested the effects of moderate changes in these quantities. Specifically, the soil conductivity was varied by a factor of 3, the albedo and emissivity of the surface were changed by 15 to 20 percent, and the effects of a gross amount of atmospheric blanketing were studied, as described. Only the last of these variations had any significant effect on the model, and other results of the atmospheric blanketing were in disagreement with other physical observations of the planet. Consequently, we find it difficult to avoid the conclusion that CO(2) must condense in large amounts relative to H(2)0. The main conclusions indicated by this study are the following. 1) The atmosphere and frost caps of Mars represent a single system with CO(2) as the only active phase. 2) The appearance and disappearance of the polar caps are adequately explained on the presumption that they are composed almost entirely of solid CO(2) with perhaps an occasional thin coating of water ice. 3) If the currently reported water-vapor observations are correct, water-ice permafrost probably exists under large regions of the planet at polar and temperate latitudes. 4) The geochemically anomalous enrichment of CO(2) relative to N(2) in the present Martian atmosphere may be a result of selective trapping of CO(2) in the solid phase at and under the surface. 5) If the basic evaporation and condensation mechanisms for CO(2) and H(2)O discussed in this article are correct, the possible migration of volatile organic compounds away from the warm temperate regions of the planet and their possible accumulation in the polar regions need to be carefully considered.

@article{doi101126science1533732136,
    author = "Leighton, Robert B. and Murray, Bruce C.",
    title = "Behavior of Carbon Dioxide and Other Volatiles on Mars",
    year = "1966",
    journal = "Science",
    abstract = "We have found that a rather simple thermal model of the Martian surface, in combination with current observations of the atmospheric composition, points strongly toward the conclusion that the polar caps of Mars consist almost entirely of frozen CO(2). This study was based upon the following principal assumptions. 1) Carbon dioxide is a major constituent of the Martian atmosphere. 2) The blanketing effect of the atmosphere is small, and due principally to the absorption band of CO(2) near 15 microns. 3) Lateral and convective heat transfer by the atmosphere is negligible. 4) The far-infrared emissivity of the Martian soil and of solid CO(2) are near unity. 5) The reflectivities of the soil and of solid CO(2) in the visible part of the spectrum are about 0.15 and 0.65, respectively. 6) Values for soil conductivity, density, and specific heat are those characteristic of powdered minerals at low gas pressure. 7) Water is a minor constituent of the Martian atmosphere, the maximum total amount in the atmosphere being 10 to 30 X 1O(-4) g cm(-2). In addition, several simplifications were made, which might have significant effects but should not alter our principal conclusions. Among these are the following. 1) Local blanketing or snowfall effects due to clouds or polar haze were ignored. 2) Dark and light areas were not differentiated in this study, although Sinton and Strong (6) have observed temperature differences between such areas. 3) The effects of local topography and microrelief were neglected. We believe that these must have quite significant effects at the higher latitudes, especially in connection with the evaporation of the remanent south polar cap. 4) Variation of reflectivity with angle of incidence of the sunlight was neglected. 5) Temperature dependence of soil conductivity and specific heat was ignored. 6) Effects of saturation of the soil by ice upon the thermal properties of the soil were neglected. Although in our main investigation we used certain specific values for the various relevant parameters, we also tested the effects of moderate changes in these quantities. Specifically, the soil conductivity was varied by a factor of 3, the albedo and emissivity of the surface were changed by 15 to 20 percent, and the effects of a gross amount of atmospheric blanketing were studied, as described. Only the last of these variations had any significant effect on the model, and other results of the atmospheric blanketing were in disagreement with other physical observations of the planet. Consequently, we find it difficult to avoid the conclusion that CO(2) must condense in large amounts relative to H(2)0. The main conclusions indicated by this study are the following. 1) The atmosphere and frost caps of Mars represent a single system with CO(2) as the only active phase. 2) The appearance and disappearance of the polar caps are adequately explained on the presumption that they are composed almost entirely of solid CO(2) with perhaps an occasional thin coating of water ice. 3) If the currently reported water-vapor observations are correct, water-ice permafrost probably exists under large regions of the planet at polar and temperate latitudes. 4) The geochemically anomalous enrichment of CO(2) relative to N(2) in the present Martian atmosphere may be a result of selective trapping of CO(2) in the solid phase at and under the surface. 5) If the basic evaporation and condensation mechanisms for CO(2) and H(2)O discussed in this article are correct, the possible migration of volatile organic compounds away from the warm temperate regions of the planet and their possible accumulation in the polar regions need to be carefully considered.",
    url = "https://doi.org/10.1126/science.153.3732.136",
    doi = "10.1126/science.153.3732.136",
    openalex = "W1987334472"
}

@misc{glasstone1968the1,
    author = "Glasstone, S",
    title = "The Book of Mars",
    year = "1968",
    howpublished = "Washington, D.C., NASA",
    note = "talkorigins\_source = {true}; raw\_reference = {Glasstone, S., 1968, The Book of Mars: Washington, D.C., NASA.}"
}

@article{doi1010160019103572900036,
    author = "McCauley, John F. and Carr, M. H. and Cutts, J. A. and Hartmann, W. K. and Masursky, H. and Milton, D. J. and Sharp, Robert P. and Wilhelms, D. E.",
    title = "Preliminary mariner 9 report on the geology of Mars",
    year = "1972",
    journal = "Icarus",
    url = "https://doi.org/10.1016/0019-1035(72)90003-6",
    doi = "10.1016/0019-1035(72)90003-6",
    openalex = "W1978262893"
}

@article{doi1010160019103574901018,
    author = "Baker, Victor R. and Milton, D. J.",
    title = "Erosion by catastrophic floods on Mars and Earth",
    year = "1974",
    journal = "Icarus",
    url = "https://doi.org/10.1016/0019-1035(74)90101-8",
    doi = "10.1016/0019-1035(74)90101-8",
    openalex = "W1986988833",
    references = "doi1023071796776, doi103133pp596"
}

@article{doi10113000167606197586593com20co2,
    author = "Sharp, Robert P. and Malin, M. C.",
    title = "Channels on Mars",
    year = "1975",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1975)86<593:com>2.0.co;2",
    doi = "10.1130/0016-7606(1975)86<593:com>2.0.co;2",
    openalex = "W2058886389"
}

@article{doi101029js082i028p04225,
    author = "Farmer, C. B. and Davies, D. W. and Holland, Alex and LaPorte, Daniel D. and Doms, P. E.",
    title = "Mars: Water vapor observations from the Viking orbiters",
    year = "1977",
    journal = "Journal of Geophysical Research Atmospheres",
    url = "https://doi.org/10.1029/js082i028p04225",
    doi = "10.1029/js082i028p04225",
    openalex = "W1970341234"
}

Measurements of Martian emission and reflection reveal wide variations of surface properties and indicate the presence of a larger atmospheric contribution to the observed radiances than was anticipated. Temperatures observed during the Viking primary mission range from 130 to 290 K. Surface thermal inertias from 1.6 to 11×10−3 cal cm−2 s−1/2 K−1 are mapped, and they correlate with surficial geologic units. An equatorial map of bolometric albedo generally correlates with prior narrowband observations. These albedos range from 0.09 to 0.43; some regional brightenings are atmospheric in origin. The photometric behavior implies quasi-Lambertian surface reflectance plus a strongly forward-scattering atmosphere. Brightness temperatures at large emission angles are strongly influenced by atmospheric infrared opacity and by the presence of rocks on the surface. The correlation and grouping of albedo and thermal inertia indicate that there are two major components of Martian surface material, with bright regions having a fine particulate covering. Winter polar temperatures show spatial and temporal variations, suggesting variation of atmospheric composition; a strong atmospheric temperature inversion exists above the south polar cap during winter. Surface CO2 condensation may also occur locally near the equator before dawn. Rising temperatures before dawn in a region near Arsia Mons imply the presence of daily local water ice fogs.

@article{doi101029js082i028p04249,
    author = "Kieffer, H. H. and Martin, T. Z. and Peterfreund, Alan and Jakosky, B. M. and Miner, E. D. and Palluconi, F. D.",
    title = "Thermal and albedo mapping of Mars during the Viking primary mission",
    year = "1977",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Measurements of Martian emission and reflection reveal wide variations of surface properties and indicate the presence of a larger atmospheric contribution to the observed radiances than was anticipated. Temperatures observed during the Viking primary mission range from 130 to 290 K. Surface thermal inertias from 1.6 to 11×10−3 cal cm−2 s−1/2 K−1 are mapped, and they correlate with surficial geologic units. An equatorial map of bolometric albedo generally correlates with prior narrowband observations. These albedos range from 0.09 to 0.43; some regional brightenings are atmospheric in origin. The photometric behavior implies quasi-Lambertian surface reflectance plus a strongly forward-scattering atmosphere. Brightness temperatures at large emission angles are strongly influenced by atmospheric infrared opacity and by the presence of rocks on the surface. The correlation and grouping of albedo and thermal inertia indicate that there are two major components of Martian surface material, with bright regions having a fine particulate covering. Winter polar temperatures show spatial and temporal variations, suggesting variation of atmospheric composition; a strong atmospheric temperature inversion exists above the south polar cap during winter. Surface CO2 condensation may also occur locally near the equator before dawn. Rising temperatures before dawn in a region near Arsia Mons imply the presence of daily local water ice fogs.",
    url = "https://doi.org/10.1029/js082i028p04249",
    doi = "10.1029/js082i028p04249",
    openalex = "W2105128256",
    references = "doi1010160019103572900097, doi1010160019103575901566, doi1010160032063368901025, doi101029js082i028p04225, doi101029js082i028p04364, doi101029js082i028p04479, doi101126science1533732136, doi101126science19442711341, doi1023072004698, openalexw1637661022"
}

@article{doi101029js082i028p04364,
    author = "Seiff, A. and Kirk, Donn B.",
    title = "Structure of the atmosphere of Mars in summer at mid-latitudes",
    year = "1977",
    journal = "Journal of Geophysical Research Atmospheres",
    url = "https://doi.org/10.1029/js082i028p04364",
    doi = "10.1029/js082i028p04364",
    openalex = "W1972466032"
}

The current status is summarized of investigations of the composition of the Martian atmosphere, in which use was made of the mass spectrometers that function as the analytical component of the molecular analysis experiments on the two Viking landers. The following points seem well established: N2, Ar-40, Ne, Kr, Xe, and the primordial isotope of Ar are present. The present atmosphere of Mars represents only a small fraction of the total amount of volatiles outgassed by the planet, so that high surface pressure and abundant water may have been present. The noble gases in the Martian atmosphere exhibit a relative abundance pattern similar to that in the earth's atmosphere and (except for Xe) to that in the primordial component of meteorites. The existence of a 'planetary component' is thus proven, supporting the arguments of those who favor a fractionation of noble gases prior to the formation of the planets. In spite of these similarities, the isotopic ratios of nitrogen, argon, and xenon indicate that the histories of the Martian and the earth's atmospheres have been very different.

@article{doi101029js082i028p04635,
    author = "Owen, Tobias and Biemann, K. and Rushneck, D. R. and Biller, J. E. and Howarth, D. W. and Lafleur, Arthur L.",
    title = "The composition of the atmosphere at the surface of Mars",
    year = "1977",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The current status is summarized of investigations of the composition of the Martian atmosphere, in which use was made of the mass spectrometers that function as the analytical component of the molecular analysis experiments on the two Viking landers. The following points seem well established: N2, Ar-40, Ne, Kr, Xe, and the primordial isotope of Ar are present. The present atmosphere of Mars represents only a small fraction of the total amount of volatiles outgassed by the planet, so that high surface pressure and abundant water may have been present. The noble gases in the Martian atmosphere exhibit a relative abundance pattern similar to that in the earth's atmosphere and (except for Xe) to that in the primordial component of meteorites. The existence of a 'planetary component' is thus proven, supporting the arguments of those who favor a fractionation of noble gases prior to the formation of the planets. In spite of these similarities, the isotopic ratios of nitrogen, argon, and xenon indicate that the histories of the Martian and the earth's atmospheres have been very different.",
    url = "https://doi.org/10.1029/js082i028p04635",
    doi = "10.1029/js082i028p04635",
    openalex = "W2091767388"
}

Mars, like Earth, may have received its volatiles in the final stages of accretion, as a veneer of volatile-rich material similar to C3V carbonaceous chondrites. The high 40 Ar/ 36 Ar ratio and low 36 Ar abundance on Mars, compared to data for other differentiated planets, suggest that Mars is depleted in volatiles relative to Earth—by a factor of 1.7 for K and 14 other moderately volatile elements and by a factor of 35 for 36 Ar and 15 other highly volatile elements. Using these two scaling factors, we have predicted martian abundances of 31 elements from terrestrial abundances. Comparison with the observed 36 Ar abundance suggests that outgassing on Mars has been about four times less complete than on Earth. Various predictions of the model can be checked against observation. The initial abundance of N, prior to escape, was about ten times the present value of 0.62 ppb, in good agreement with an independent estimate based on the observed enhancement in the martian 15 N/ 14 N ratio. The initial water content corresponds to a 9-m layer, close to the value of ≤13 m inferred from the lack of an 18 O/ 16 O fractionation. The predicted crustal Cl/S ratio of 0.23 agrees exactly with the value measured for martian dust; we estimate the thickness of this dust layer to be about 70 m. The predicted surface abundance of carbon, 290 g/cm 2, is 70 times greater than the atmospheric CO 2 value, but the CaCO 3 content inferred for martian dust could account for at least one-quarter of the predicted value. The past atmospheric pressure, prior to formation of carbonates, could have been as high as 140 mbar, and possibly even 500 mbar. Finally, the predicted 129 Xe/ 132 Xe ratio of 2.96 agrees fairly well with the observed value of 2.5 +2 –1. From the limited data available thus far, a curious dichotomy seems to be emerging among differentiated planets in the inner solar system. Two large planets (Earth and Venus) are fairly rich in volatiles, whereas three small planets (Mars, the moon, and the eucrite parent body—presumably the asteroid 4 Vesta) are poorer in volatiles by at least an order of magnitude. None of the obvious mechanisms seems capable of explaining this trend, and so we can only speculate that the same mechanism that stunted the growth of the smaller bodies prevented them from collecting their share of volatiles. But why then did the parent bodies of the chondrites and shergottites fare so much better? One of the driving forces behind the exploration of the solar system has always been the realization that these studies can provide essential clues to the intricate network of puzzles associated with the origin of life and its prevalence in the universe. In our own immediate neighborhood, Mars has always seemed to be the planet most likely to harbor extraterrestrial life, so the environment we have found in the vicinity of the two Viking landers is rather disappointing in this context. But the perspective we have gained through the present investigation suggests that this is not a necessary condition for planets at the distance of Mars from a solar-type central star. In other words, if it turns out that Mars is completely devoid of life, this does not mean that the zones around stars in which habitable planets can exist are much narrower than has been thought. Suppose Mars had been a larger planet—the size of Earth or Venus—and therefore had accumulated a thicker veneer and had also developed global tectonic activity on the scale exhibited by Earth. A much larger volatile reservoir would now be available, there would be repeated opportunities for tapping that reservoir, and the increased gravitational field would limit escape from the upper atmosphere. Such a planet could have produced and maintained a much thicker atmosphere, which should have permitted at least an intermittently clement climate to exist. How different would such a planet be from the present Mars? Could a stable, warm climate be maintained? It seems conceivable that an increase in the size of Mars might have compensated for its greater distance from the sun and that the life zone around our star would have been enlarged accordingly.

@article{doi101126science1984316453,
    author = "Anders, Edward and Owen, Tobias",
    title = "Mars and Earth: Origin and Abundance of Volatiles",
    year = "1977",
    journal = "Science",
    abstract = "Mars, like Earth, may have received its volatiles in the final stages of accretion, as a veneer of volatile-rich material similar to C3V carbonaceous chondrites. The high 40 Ar/ 36 Ar ratio and low 36 Ar abundance on Mars, compared to data for other differentiated planets, suggest that Mars is depleted in volatiles relative to Earth—by a factor of 1.7 for K and 14 other moderately volatile elements and by a factor of 35 for 36 Ar and 15 other highly volatile elements. Using these two scaling factors, we have predicted martian abundances of 31 elements from terrestrial abundances. Comparison with the observed 36 Ar abundance suggests that outgassing on Mars has been about four times less complete than on Earth. Various predictions of the model can be checked against observation. The initial abundance of N, prior to escape, was about ten times the present value of 0.62 ppb, in good agreement with an independent estimate based on the observed enhancement in the martian 15 N/ 14 N ratio. The initial water content corresponds to a 9-m layer, close to the value of ≤13 m inferred from the lack of an 18 O/ 16 O fractionation. The predicted crustal Cl/S ratio of 0.23 agrees exactly with the value measured for martian dust; we estimate the thickness of this dust layer to be about 70 m. The predicted surface abundance of carbon, 290 g/cm 2, is 70 times greater than the atmospheric CO 2 value, but the CaCO 3 content inferred for martian dust could account for at least one-quarter of the predicted value. The past atmospheric pressure, prior to formation of carbonates, could have been as high as 140 mbar, and possibly even 500 mbar. Finally, the predicted 129 Xe/ 132 Xe ratio of 2.96 agrees fairly well with the observed value of 2.5 +2 –1. From the limited data available thus far, a curious dichotomy seems to be emerging among differentiated planets in the inner solar system. Two large planets (Earth and Venus) are fairly rich in volatiles, whereas three small planets (Mars, the moon, and the eucrite parent body—presumably the asteroid 4 Vesta) are poorer in volatiles by at least an order of magnitude. None of the obvious mechanisms seems capable of explaining this trend, and so we can only speculate that the same mechanism that stunted the growth of the smaller bodies prevented them from collecting their share of volatiles. But why then did the parent bodies of the chondrites and shergottites fare so much better? One of the driving forces behind the exploration of the solar system has always been the realization that these studies can provide essential clues to the intricate network of puzzles associated with the origin of life and its prevalence in the universe. In our own immediate neighborhood, Mars has always seemed to be the planet most likely to harbor extraterrestrial life, so the environment we have found in the vicinity of the two Viking landers is rather disappointing in this context. But the perspective we have gained through the present investigation suggests that this is not a necessary condition for planets at the distance of Mars from a solar-type central star. In other words, if it turns out that Mars is completely devoid of life, this does not mean that the zones around stars in which habitable planets can exist are much narrower than has been thought. Suppose Mars had been a larger planet—the size of Earth or Venus—and therefore had accumulated a thicker veneer and had also developed global tectonic activity on the scale exhibited by Earth. A much larger volatile reservoir would now be available, there would be repeated opportunities for tapping that reservoir, and the increased gravitational field would limit escape from the upper atmosphere. Such a planet could have produced and maintained a much thicker atmosphere, which should have permitted at least an intermittently clement climate to exist. How different would such a planet be from the present Mars? Could a stable, warm climate be maintained? It seems conceivable that an increase in the size of Mars might have compensated for its greater distance from the sun and that the life zone around our star would have been enlarged accordingly.",
    url = "https://doi.org/10.1126/science.198.4316.453",
    doi = "10.1126/science.198.4316.453",
    openalex = "W2040490498"
}

@article{doi1010160016703779901807,
    author = "Morgan, John W. and Anders, Edward",
    title = "Chemical composition of Mars",
    year = "1979",
    journal = "Geochimica et Cosmochimica Acta",
    url = "https://doi.org/10.1016/0016-7037(79)90180-7",
    doi = "10.1016/0016-7037(79)90180-7",
    openalex = "W1974010803"
}

@article{doi101016001910358190035x,
    author = "Lucchitta, B",
    title = "Mars and Earth: Comparison of cold-climate features",
    year = "1981",
    journal = "Icarus",
    url = "https://doi.org/10.1016/0019-1035(81)90035-x",
    doi = "10.1016/0019-1035(81)90035-x",
    openalex = "W2041324533"
}

@article{doi1010160019103581900415,
    author = "Clark, B.",
    title = "The salts of Mars",
    year = "1981",
    journal = "Icarus",
    url = "https://doi.org/10.1016/0019-1035(81)90041-5",
    doi = "10.1016/0019-1035(81)90041-5",
    openalex = "W2165943580"
}

More than 15 years of planetary exploration of Mars have given insight into the geologic processes that have shaped its surface. The newly acquired Viking data have shown that volcanism is one of the most important geologic processes operating on Mars throughout its history. In situ chemical analyses of Martian soil by the Viking lander spacecraft indicate mafic to ultramafic source rocks. This is consistent both with available remote sensing data, which indicate the presence of mafic minerals such as pyroxene and olivine, and with petrologic modeling, based on available geophysical data which suggest that Martian lavas are probably iron rich and ultramafic. These data strongly suggest that basaltic volcanism is widespread on Mars, and much of the photogeological data may be studied in this context. Photogeological analysis of the Martian surface has shown two main types of volcanic morphologies: the first type is central volcanoes, which are volcanic landforms developed by continued and prolonged eruption from a point source vent. This category includes (1) shields, the classic low‐profile volcanic mountains of which Olympus Mons is the most spectacular example, (2) domes, steep‐sided constructs, such as Tharsis Tholus, that may represent lower rates of eruption than the shields or, possibly, more silicic lava compositions, (3) highland patera, radially textured low‐profile volcanoes that occur in the cratered terrain and are interpreted as ash shields, (4) Alba Patera, an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree, and (5) various small features such as cinder cones. The second major category is volcanic plains, which are units recognized by several criteria, of which the presence of mare ridges and flow lobes are the most useful. Volcanic plains are subdivided into four main groups: (1) simple flows, broad, smooth to rolling plains that contain numerous mare‐type ridges but no flow lobes, interpreted as being composed of thick, single‐cooling units, (2) complex flows, displaying multiple overlapping flow lobes interpreted to be indicative of thin, multiple‐cooling units, (3) undifierentiated flows, plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers, and (4) questionable plains, volcanic(?) units heavily modified by other processes (erosion, tectonism, etc.) so that their origins are uncertain. When these categories of volcanic morphologies are combined with relative age data provided by crater statistics, a volcanic history for Mars can be derived as follows: Early heavy bombardment of Mars was accompanied and followed by small‐scale fluvial channeling, extensive flood volcanism (the plateau plains), and ash shield volcanism in the cratered terrain. Shortly after this time, less extensive flood volcanism continued to resurface the planet during formation of the northern/southern hemisphere dichotomy. Central volcanism became more prominent with the development of the Alba Patera center as well as the older shields and domes of the northern hemisphere (early Tharsis and Elysium regions). The development of the Tharsis and Elysium uplifts may have triggered the release of large‐scale catastrophic floods, producing large channels. Continued uplift and lithospheric thinning concentrated volcanic activity in the Tharsis region, producing large shield volcanoes and extensive lava plains. Both central vent and plains volcanism have been active throughout Martian history, but the volumes of extrusion have gradually decreased with time. This is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time, gradually ‘turning off’ the volcanism. Although many questions remain regarding Martian volcanism, the Viking data have provided a remarkable, detailed overview of the probable nature of the volcanic history of Mars.

@article{doi101029rg019i001p00013,
    author = "Greeley, R. and Spudis, P. D.",
    title = "Volcanism on Mars",
    year = "1981",
    journal = "Reviews of Geophysics",
    abstract = "More than 15 years of planetary exploration of Mars have given insight into the geologic processes that have shaped its surface. The newly acquired Viking data have shown that volcanism is one of the most important geologic processes operating on Mars throughout its history. In situ chemical analyses of Martian soil by the Viking lander spacecraft indicate mafic to ultramafic source rocks. This is consistent both with available remote sensing data, which indicate the presence of mafic minerals such as pyroxene and olivine, and with petrologic modeling, based on available geophysical data which suggest that Martian lavas are probably iron rich and ultramafic. These data strongly suggest that basaltic volcanism is widespread on Mars, and much of the photogeological data may be studied in this context. Photogeological analysis of the Martian surface has shown two main types of volcanic morphologies: the first type is central volcanoes, which are volcanic landforms developed by continued and prolonged eruption from a point source vent. This category includes (1) shields, the classic low‐profile volcanic mountains of which Olympus Mons is the most spectacular example, (2) domes, steep‐sided constructs, such as Tharsis Tholus, that may represent lower rates of eruption than the shields or, possibly, more silicic lava compositions, (3) highland patera, radially textured low‐profile volcanoes that occur in the cratered terrain and are interpreted as ash shields, (4) Alba Patera, an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree, and (5) various small features such as cinder cones. The second major category is volcanic plains, which are units recognized by several criteria, of which the presence of mare ridges and flow lobes are the most useful. Volcanic plains are subdivided into four main groups: (1) simple flows, broad, smooth to rolling plains that contain numerous mare‐type ridges but no flow lobes, interpreted as being composed of thick, single‐cooling units, (2) complex flows, displaying multiple overlapping flow lobes interpreted to be indicative of thin, multiple‐cooling units, (3) undifierentiated flows, plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers, and (4) questionable plains, volcanic(?) units heavily modified by other processes (erosion, tectonism, etc.) so that their origins are uncertain. When these categories of volcanic morphologies are combined with relative age data provided by crater statistics, a volcanic history for Mars can be derived as follows: Early heavy bombardment of Mars was accompanied and followed by small‐scale fluvial channeling, extensive flood volcanism (the plateau plains), and ash shield volcanism in the cratered terrain. Shortly after this time, less extensive flood volcanism continued to resurface the planet during formation of the northern/southern hemisphere dichotomy. Central volcanism became more prominent with the development of the Alba Patera center as well as the older shields and domes of the northern hemisphere (early Tharsis and Elysium regions). The development of the Tharsis and Elysium uplifts may have triggered the release of large‐scale catastrophic floods, producing large channels. Continued uplift and lithospheric thinning concentrated volcanic activity in the Tharsis region, producing large shield volcanoes and extensive lava plains. Both central vent and plains volcanism have been active throughout Martian history, but the volumes of extrusion have gradually decreased with time. This is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time, gradually ‘turning off’ the volcanism. Although many questions remain regarding Martian volcanism, the Viking data have provided a remarkable, detailed overview of the probable nature of the volcanic history of Mars.",
    url = "https://doi.org/10.1029/rg019i001p00013",
    doi = "10.1029/rg019i001p00013",
    openalex = "W1969376448"
}

A series of postulated ignimbrite units is mapped in the Amazonis, Memnonia, and Aeolis quadrangles of Mars. The units cover about 2.2×10 6 km 2 within a broad but discontinuous and irregular belt trending east‐west along the highland‐lowland boundary. The ignimbrites overlie parts of the western and southern aureole materials of Olympus Mons but are embayed in places by the lava plains of the lowlands. Stratigraphic relations between the basalt flows from the Tharsis Montes region and the ignimbrites are not clearly defined; crater counts suggest that the younger ignimbrites postdate the lava flows. Crater counts per square kilometer for the ignimbrites range from 7.29±1.95×10 −4 to 6.36±2.01×10 −5 for craters larger than 1 km in diameter. The ignimbrite materials form thick (≥100 m), extensive, relatively flat sheets that are smooth to grooved or gently undulating. Grooved surfaces appear to be yardangs and, in most places, are not alined with prevailing wind directions. The seven mapped ignimbrite units are characterized by morphologic expression, stratigraphic position, and crater counts. Similarities to ignimbrites in the Pancake Range of central Nevada include (1) rounded patches of smooth, high‐albedo, nonwelded material superposed on jointed, low‐albedo, welded material, (2) local complementary joint sets in welded materials, and (3) thick flow sheets of great areal extent that follow but subdue underlying topography. Four major eruptive centers occur in areas where units are thickest and where a dominant, NNW‐SSE structural trend is expressed locally by unit margins, elongate collapse features, and normal faulting. A minimum volume of 3.85×10 6 km 3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations.

@article{doi101029jb087ib02p01179,
    author = "Scott, D. H. and Tanaka, Kenneth L.",
    title = "Ignimbrites of Amazonis Planitia Region of Mars",
    year = "1982",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "A series of postulated ignimbrite units is mapped in the Amazonis, Memnonia, and Aeolis quadrangles of Mars. The units cover about 2.2×10 6 km 2 within a broad but discontinuous and irregular belt trending east‐west along the highland‐lowland boundary. The ignimbrites overlie parts of the western and southern aureole materials of Olympus Mons but are embayed in places by the lava plains of the lowlands. Stratigraphic relations between the basalt flows from the Tharsis Montes region and the ignimbrites are not clearly defined; crater counts suggest that the younger ignimbrites postdate the lava flows. Crater counts per square kilometer for the ignimbrites range from 7.29±1.95×10 −4 to 6.36±2.01×10 −5 for craters larger than 1 km in diameter. The ignimbrite materials form thick (≥100 m), extensive, relatively flat sheets that are smooth to grooved or gently undulating. Grooved surfaces appear to be yardangs and, in most places, are not alined with prevailing wind directions. The seven mapped ignimbrite units are characterized by morphologic expression, stratigraphic position, and crater counts. Similarities to ignimbrites in the Pancake Range of central Nevada include (1) rounded patches of smooth, high‐albedo, nonwelded material superposed on jointed, low‐albedo, welded material, (2) local complementary joint sets in welded materials, and (3) thick flow sheets of great areal extent that follow but subdue underlying topography. Four major eruptive centers occur in areas where units are thickest and where a dominant, NNW‐SSE structural trend is expressed locally by unit margins, elongate collapse features, and normal faulting. A minimum volume of 3.85×10 6 km 3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations.",
    url = "https://doi.org/10.1029/jb087ib02p01179",
    doi = "10.1029/jb087ib02p01179",
    openalex = "W2172116764"
}

The number of Martian impact basins, once thought deficient owing to a low number of impactors, has been significantly increased through the identification of structural imprints that remain even after nearly complete erasure of basin massifs. Five ancient multiringed impact basins were selected for detailed study and exhibit a systematic pattern of rejuvenation of the multiring plan through endogenic modification. Concentric zones of unstable terrain are believed to reflect deep‐seated, impact‐related fractures that have localized regional igneous processes in a manner analogous with the basin‐controlled distribution of basalts on the moon. Most Martian outflow channels were found to originate along the unstable ring zones. Hydrothermal melting and temporary confinement of channel source materials at sites analogous to lunar sinuous rille source regions are proposed to play an important role in the distribution of Martian outflow channels. Ancient basins also can be delineated by the concentric pattern of topographically and structurally controlled narrow valley networks that are particularly abundant along the outer rings where basin ejecta deposits occur. Remnant massifs and scarps commonly exhibit extensive furrowing by narrow valley networks, perhaps due to a different paleoclimate or sapping during a period of geothermal melting of trapped ices. The systematic patterns of valley networks, stable and unstable annuli, scarps, and massifs provide bases for interpreting impact structure in general and for recognizing multiringed structures elsewhere. The Chryse basin, in particular, is proposed to represent a major multiringed structure that controlled the formation and distribution of eastern Valles Marineris and the chaotic terrains of Margaritifer Sinus in response to volcanism/tectonism related to Tharsis. We conclude that (1) Mars is probably not deficient in large‐body impactors; (2) the multiring patterns of basins represent deep‐seated fracture zones that can be reexposed through subsequent volcanism, hydrothermal activity, sapping, and differential erosion; (3) many Martian terrains and features (e.g., chaotic terrains and outflow channels) are controlled by ancient basins; and (4) the resurrection and destruction of impact basins reveal an important third dimension (depth) for interpreting impact basin formation.

@article{doi101029jb087ib12p09803,
    author = "Schultz, P. H. and Schultz, Richard A. and Rogers, J.",
    title = "The structure and evolution of ancient impact basins on Mars",
    year = "1982",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The number of Martian impact basins, once thought deficient owing to a low number of impactors, has been significantly increased through the identification of structural imprints that remain even after nearly complete erasure of basin massifs. Five ancient multiringed impact basins were selected for detailed study and exhibit a systematic pattern of rejuvenation of the multiring plan through endogenic modification. Concentric zones of unstable terrain are believed to reflect deep‐seated, impact‐related fractures that have localized regional igneous processes in a manner analogous with the basin‐controlled distribution of basalts on the moon. Most Martian outflow channels were found to originate along the unstable ring zones. Hydrothermal melting and temporary confinement of channel source materials at sites analogous to lunar sinuous rille source regions are proposed to play an important role in the distribution of Martian outflow channels. Ancient basins also can be delineated by the concentric pattern of topographically and structurally controlled narrow valley networks that are particularly abundant along the outer rings where basin ejecta deposits occur. Remnant massifs and scarps commonly exhibit extensive furrowing by narrow valley networks, perhaps due to a different paleoclimate or sapping during a period of geothermal melting of trapped ices. The systematic patterns of valley networks, stable and unstable annuli, scarps, and massifs provide bases for interpreting impact structure in general and for recognizing multiringed structures elsewhere. The Chryse basin, in particular, is proposed to represent a major multiringed structure that controlled the formation and distribution of eastern Valles Marineris and the chaotic terrains of Margaritifer Sinus in response to volcanism/tectonism related to Tharsis. We conclude that (1) Mars is probably not deficient in large‐body impactors; (2) the multiring patterns of basins represent deep‐seated fracture zones that can be reexposed through subsequent volcanism, hydrothermal activity, sapping, and differential erosion; (3) many Martian terrains and features (e.g., chaotic terrains and outflow channels) are controlled by ancient basins; and (4) the resurrection and destruction of impact basins reveal an important third dimension (depth) for interpreting impact basin formation.",
    url = "https://doi.org/10.1029/jb087ib12p09803",
    doi = "10.1029/jb087ib12p09803",
    openalex = "W2142545238"
}

@article{openalexw2996298354,
    author = "Dreibus, G. and Wänke, H.",
    title = "Mars, a volatile-rich planet",
    year = "1985",
    journal = "Meteoritics and Planetary Science",
    openalex = "W2996298354"
}

A detailed planetwide stratigraphy for Mars has been developed from global mapping based on Viking images and crater counting of geologic units. The original Noachian, Hesperian, and Amazonian Systems are divided into eight series corresponding to stratigraphic referents. Characteristic crater densities and material referents of each series are (1) Lower Noachian [N(16)] (number of craters > 16 km in diameter per 10 6 km 2) > 200] basement material; (2) Middle Noachian [N(16) = 100–200] cratered terrain material; (3) Upper Noachian [N(16) = 25–100; N(5) = 200–400] intercrater plains material; (4) Lower Hesperian [N(5) = 125–200] ridged plains material; (5) Upper Hesperian [N(5) = 67–125; N(2) = 400–750] complex plains material; (6) Lower Amazonian [N(2) = 150–400] smooth plains material in southern Acidalia Planitia; (7) Middle Amazonian [N(2) = 40–150] lava flows in Amazonis Planitia; and (8) Upper Amazonian [N(2) < 40] flood‐plain material in southern Elysium Planitia. Correlations between various crater size‐frequency distributions of highland materials on the moon and Mars suggest that rocks of the Middle Noachian Series are about 3.92–3.85 b.y. old. Stratigraphic ages compiled for units and features of various origins show that volcanism, tectonism, and meteorite bombardment have generally decreased through Mars' geologic history. In recent time, surficial processes have dominated the formation and modification of rock units. The overall stratigraphy of Mars is complex, however, because of temporal and spatial variations in geologic activity.

@article{doi101029jb091ib13p0e139,
    author = "Tanaka, Kenneth L.",
    title = "The stratigraphy of Mars",
    year = "1986",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "A detailed planetwide stratigraphy for Mars has been developed from global mapping based on Viking images and crater counting of geologic units. The original Noachian, Hesperian, and Amazonian Systems are divided into eight series corresponding to stratigraphic referents. Characteristic crater densities and material referents of each series are (1) Lower Noachian [N(16)] (number of craters > 16 km in diameter per 10 6 km 2) > 200] basement material; (2) Middle Noachian [N(16) = 100–200] cratered terrain material; (3) Upper Noachian [N(16) = 25–100; N(5) = 200–400] intercrater plains material; (4) Lower Hesperian [N(5) = 125–200] ridged plains material; (5) Upper Hesperian [N(5) = 67–125; N(2) = 400–750] complex plains material; (6) Lower Amazonian [N(2) = 150–400] smooth plains material in southern Acidalia Planitia; (7) Middle Amazonian [N(2) = 40–150] lava flows in Amazonis Planitia; and (8) Upper Amazonian [N(2) < 40] flood‐plain material in southern Elysium Planitia. Correlations between various crater size‐frequency distributions of highland materials on the moon and Mars suggest that rocks of the Middle Noachian Series are about 3.92–3.85 b.y. old. Stratigraphic ages compiled for units and features of various origins show that volcanism, tectonism, and meteorite bombardment have generally decreased through Mars' geologic history. In recent time, surficial processes have dominated the formation and modification of rock units. The overall stratigraphy of Mars is complex, however, because of temporal and spatial variations in geologic activity.",
    url = "https://doi.org/10.1029/jb091ib13p0e139",
    doi = "10.1029/jb091ib13p0e139",
    openalex = "W2113865155",
    references = "doi101007bf00577878, doi1010160019103572900036, doi1010160019103578900489, doi101016001910358190035x, doi101029jb084ib06p02929, doi101029jb087ib02p01179, doi101029jb087ib12p09803, doi101029rg019i001p00013, doi10113000167606197586593com20co2, openalexw2302969081"
}

High-resolution Viking orbiter images show evidence for quasi-viscous relaxation of topography. The relaxation is believed to be due to creep deformation of ice in near-surface materials. The global distribution of the inferred ground ice shows a pronounced latitudinal dependence. The equatorial regions of Mars appear to be ice-poor, while the heavily cratered terrain poleward of +/- 30 degrees latitude appears to be ice-rich. The style of creep poleward of +/- 30 degrees varies with latitude, possibly due to variations in ice rheology with temperature. The distribution suggests that ice at low latitudes, which is not in equilibrium with the present atmosphere, has been lost via sublimation and diffusion through the regolith, thereby causing a net poleward transport of ice over martian history.

@article{doi101126science2314735249,
    author = "Squyres, S. W. and Carr, M. H.",
    title = "Geomorphic Evidence for the Distribution of Ground Ice on Mars",
    year = "1986",
    journal = "Science",
    abstract = "High-resolution Viking orbiter images show evidence for quasi-viscous relaxation of topography. The relaxation is believed to be due to creep deformation of ice in near-surface materials. The global distribution of the inferred ground ice shows a pronounced latitudinal dependence. The equatorial regions of Mars appear to be ice-poor, while the heavily cratered terrain poleward of +/- 30 degrees latitude appears to be ice-rich. The style of creep poleward of +/- 30 degrees varies with latitude, possibly due to variations in ice rheology with temperature. The distribution suggests that ice at low latitudes, which is not in equilibrium with the present atmosphere, has been lost via sublimation and diffusion through the regolith, thereby causing a net poleward transport of ice over martian history.",
    url = "https://doi.org/10.1126/science.231.4735.249",
    doi = "10.1126/science.231.4735.249",
    openalex = "W2056216751"
}

@article{doi1010160019103587901473,
    author = "Pollack, James B. and Kasting, James F. and Richardson, Steven M. and Poliakoff, K.",
    title = "The case for a wet, warm climate on early Mars",
    year = "1987",
    journal = "Icarus",
    url = "https://doi.org/10.1016/0019-1035(87)90147-3",
    doi = "10.1016/0019-1035(87)90147-3",
    openalex = "W2073976878",
    references = "doi101029js082i028p04249"
}

The origin of the fundamental crustal dichotomy on Mars remains the outstanding unsolved problem in martian geologic evolution. The hypothesis that this dichotomy is due to a single giant (mega) impact early in martian history is tested by comparing the observed number of large impact basins on Mars with the number expected from a D −2 distribution. This test is based on the assumption that the mega‐impact Borealis Basin is the largest member of such a distribution. The difference between observed and “expected” basins is the number of “missing” basins that might have been obscured by subsequent geologic events. If the Borealis Basin were the largest member of a D −2 impact population, there would be a very large number of “missing” basins on Mars: 1 larger than 5000 km, 10 larger than 2000 km and 40‐50 larger than about 1000 km diameter. The area occupied by these “missing” basins (allowing for overlap) is too large to be hidden by the younger surface units. A large population of presently unrecognized large impact basins would have to be located in the well preserved cratered highlands. By contrast, if Chryse is the largest member of a D −2 impact population, the more modest number of “missing” basins could in principle be confined to areas of Mars that have been resurfaced or reworked by subsequent geologic processes. A possible alternative to the mega‐impact hypothesis is that the crustal dichotomy is due to the cumulative effects of multiple overlapping large (but not giant) impacts.

@article{doi101029gl015i003p00229,
    author = "Frey, Herbert and Schultz, Richard A.",
    title = "Large impact basins and the mega‐impact origin for the crustal dichotomy on Mars",
    year = "1988",
    journal = "Geophysical Research Letters",
    abstract = "The origin of the fundamental crustal dichotomy on Mars remains the outstanding unsolved problem in martian geologic evolution. The hypothesis that this dichotomy is due to a single giant (mega) impact early in martian history is tested by comparing the observed number of large impact basins on Mars with the number expected from a D −2 distribution. This test is based on the assumption that the mega‐impact Borealis Basin is the largest member of such a distribution. The difference between observed and “expected” basins is the number of “missing” basins that might have been obscured by subsequent geologic events. If the Borealis Basin were the largest member of a D −2 impact population, there would be a very large number of “missing” basins on Mars: 1 larger than 5000 km, 10 larger than 2000 km and 40‐50 larger than about 1000 km diameter. The area occupied by these “missing” basins (allowing for overlap) is too large to be hidden by the younger surface units. A large population of presently unrecognized large impact basins would have to be located in the well preserved cratered highlands. By contrast, if Chryse is the largest member of a D −2 impact population, the more modest number of “missing” basins could in principle be confined to areas of Mars that have been resurfaced or reworked by subsequent geologic processes. A possible alternative to the mega‐impact hypothesis is that the crustal dichotomy is due to the cumulative effects of multiple overlapping large (but not giant) impacts.",
    url = "https://doi.org/10.1029/gl015i003p00229",
    doi = "10.1029/gl015i003p00229",
    openalex = "W2115005606"
}

@article{doi1010160019103589900274,
    author = "Parker, T. J. and Saunders, R. S. and Schneeberger, Dale M.",
    title = "Transitional morphology in West Deuteronilus Mensae, Mars: Implications for modification of the lowland/upland boundary",
    year = "1989",
    journal = "Icarus",
    url = "https://doi.org/10.1016/0019-1035(89)90027-4",
    doi = "10.1016/0019-1035(89)90027-4",
    openalex = "W2004019546"
}

The space environment of Mars is largely determined by its lack of a substantial planetary magnetic field. In contrast to Earth, Mars does not have radiation belts or an auroral “oval,” and its perturbation of the interplanetary medium or solar wind is confined to a relatively small volume. Moreover, the direct interaction of the solar wind plasma with the Martian atmosphere produces a distinctive local energetic particle population of planetary origin, which provides evidence of the possibly significant scavenging of certain elements from Mars over the life of the solar system. In this paper we describe the general characteristics of near‐Mars space, as it is known today, including both the ambient interplanetary environment and the ionosphere, upper atmosphere, and regions above that are affected by the presence of Mars.

@article{doi10102991rg00066,
    author = "Luhmann, J. G. and Brace, L. H.",
    title = "Near‐Mars space",
    year = "1991",
    journal = "Reviews of Geophysics",
    abstract = "The space environment of Mars is largely determined by its lack of a substantial planetary magnetic field. In contrast to Earth, Mars does not have radiation belts or an auroral “oval,” and its perturbation of the interplanetary medium or solar wind is confined to a relatively small volume. Moreover, the direct interaction of the solar wind plasma with the Martian atmosphere produces a distinctive local energetic particle population of planetary origin, which provides evidence of the possibly significant scavenging of certain elements from Mars over the life of the solar system. In this paper we describe the general characteristics of near‐Mars space, as it is known today, including both the ambient interplanetary environment and the ionosphere, upper atmosphere, and regions above that are affected by the presence of Mars.",
    url = "https://doi.org/10.1029/91rg00066",
    doi = "10.1029/91rg00066",
    openalex = "W2108705634"
}

@article{doi101038352589a0,
    author = "Baker, Victor R. and Strom, R. G. and Gulick, V. C. and Kargel, Jeffrey S. and Komatsu, G. and Kale, Vivek",
    title = "Ancient oceans, ice sheets and the hydrological cycle on Mars",
    year = "1991",
    journal = "Nature",
    url = "https://doi.org/10.1038/352589a0",
    doi = "10.1038/352589a0",
    openalex = "W2019919661",
    references = "doi1010160019103574901018, doi101016001910358190035x, doi1010160019103587901473, doi1010160019103589900274, doi101029jb084ib06p02995, doi101029jb094ib06p07685, doi101038333313a0, doi101038342139a0, doi1011300091761319910190547lpoeef23co2, schidlowski1988a, vidal1985earths"
}

The primary objective of the Mars Observer laser altimeter (MOLA) investigation is to determine globally the topography of Mars at a level suitable for addressing problems in geology and geophysics. Secondary objectives are to characterize the 1064‐nm wavelength surface reflectivity of Mars to contribute to analyses of global surface mineralogy and seasonal albedo changes, to assist in addressing problems in atmospheric circulation, and to provide geodetic control and topographic context for the assessment of possible future Mars landing sites. The principal components of MOLA are a diode‐pumped, neodymium‐doped yttrium aluminum garnet laser transmitter that emits 1064‐nm wavelength laser pulses, a 0.5‐m‐diameter telescope, a silicon avalanche photodiode detector, and a time interval unit with 10‐ns resolution. MOLA will provide measurements of the topography of Mars within approximately 160‐m footprints and a center‐to‐center along‐track footprint spacing of 300 m along the Mars Observer subspacecraft ground track. The elevation measurements will be quantized with 1.5 m vertical resolution before correction for orbit‐ and pointing‐induced errors. MOLA profiles will be assembled into a global 0.2° × 0.2° grid that will be referenced to Mars' center of mass with an absolute accuracy of approximately 30 m. Other data products will include a global grid of topographic gradients, corrected individual profiles, and a global 0.2° × 0.2° grid of 1064‐nm surface reflectivity.

@article{doi10102992je00341,
    author = "Zuber, M. T. and Smith, David E. and Solomon, Sean C. and Muhleman, D. O. and Head, J. W. and Garvin, J. B. and Abshire, James B. and Bufton, Jack L.",
    title = "The Mars Observer laser altimeter investigation",
    year = "1992",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The primary objective of the Mars Observer laser altimeter (MOLA) investigation is to determine globally the topography of Mars at a level suitable for addressing problems in geology and geophysics. Secondary objectives are to characterize the 1064‐nm wavelength surface reflectivity of Mars to contribute to analyses of global surface mineralogy and seasonal albedo changes, to assist in addressing problems in atmospheric circulation, and to provide geodetic control and topographic context for the assessment of possible future Mars landing sites. The principal components of MOLA are a diode‐pumped, neodymium‐doped yttrium aluminum garnet laser transmitter that emits 1064‐nm wavelength laser pulses, a 0.5‐m‐diameter telescope, a silicon avalanche photodiode detector, and a time interval unit with 10‐ns resolution. MOLA will provide measurements of the topography of Mars within approximately 160‐m footprints and a center‐to‐center along‐track footprint spacing of 300 m along the Mars Observer subspacecraft ground track. The elevation measurements will be quantized with 1.5 m vertical resolution before correction for orbit‐ and pointing‐induced errors. MOLA profiles will be assembled into a global 0.2° × 0.2° grid that will be referenced to Mars' center of mass with an absolute accuracy of approximately 30 m. Other data products will include a global grid of topographic gradients, corrected individual profiles, and a global 0.2° × 0.2° grid of 1064‐nm surface reflectivity.",
    url = "https://doi.org/10.1029/92je00341",
    doi = "10.1029/92je00341",
    openalex = "W2048184437",
    references = "doi101029jb090ib14p12623"
}

The Mars Observer magnetic fields investigation will provide fast vector measurements of the Martian magnetic field over a wide dynamic range. The fundamental objectives of this investigation are (1) to establish the nature of the magnetic field of Mars, (2) to develop appropriate models for its representation, which take into account the internal sources of magnetism and the effects of the interaction with the solar wind, and (3) to map the Martian crustal remanent field to a resolution consistent with the Mars Observer orbit altitude and ground track separation. The basic instrumentation complement implemented for this mission is a synergistic combination of a dual, triaxial, flux gate magnetometer system and an electron reflectometer with sensors mounted on a spacecraft boom. The dual magnetometer system allows the real‐time estimation and correction of spacecraft‐generated fields, while the electron reflectometer provides remote magnetic field sensing capabilities. These instruments have an extensive spaceflight heritage, and similar versions of the same have been flown in numerous missions like Voyager, Magsat, International Solar Polar mission (ISPM), Giotto, Active Magnetospheric Particle Tracer Explorers, and Global Geospace Science (GGS). Depending on the telemetry rate supported, a minimum of 2–16 vector samples per second will be acquired. The instrument is microprocessor controlled, can be partially reprogrammed in flight, and supports the packet telemetry protocol implemented for Mars Observer.

@article{doi10102992je00344,
    author = "Acuña, M. H. and Connerney, J. E. P. and Wasilewski, P. J. and Lin, R. P. and Anderson, K. A. and Carlson, C. W. and McFadden, J. and Curtis, D. W. and Rème, H. and Cros, A. and Médale, J. L. and Sauvaud, J. A. and d’Uston, C. and Bauer, S. J. and Cloutier, P. A. and Mayhew, M. A. and Ness, N. F.",
    title = "Mars Observer magnetic fields investigation",
    year = "1992",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Mars Observer magnetic fields investigation will provide fast vector measurements of the Martian magnetic field over a wide dynamic range. The fundamental objectives of this investigation are (1) to establish the nature of the magnetic field of Mars, (2) to develop appropriate models for its representation, which take into account the internal sources of magnetism and the effects of the interaction with the solar wind, and (3) to map the Martian crustal remanent field to a resolution consistent with the Mars Observer orbit altitude and ground track separation. The basic instrumentation complement implemented for this mission is a synergistic combination of a dual, triaxial, flux gate magnetometer system and an electron reflectometer with sensors mounted on a spacecraft boom. The dual magnetometer system allows the real‐time estimation and correction of spacecraft‐generated fields, while the electron reflectometer provides remote magnetic field sensing capabilities. These instruments have an extensive spaceflight heritage, and similar versions of the same have been flown in numerous missions like Voyager, Magsat, International Solar Polar mission (ISPM), Giotto, Active Magnetospheric Particle Tracer Explorers, and Global Geospace Science (GGS). Depending on the telemetry rate supported, a minimum of 2–16 vector samples per second will be acquired. The instrument is microprocessor controlled, can be partially reprogrammed in flight, and supports the packet telemetry protocol implemented for Mars Observer.",
    url = "https://doi.org/10.1029/92je00344",
    doi = "10.1029/92je00344",
    openalex = "W2012600981"
}

A large number of anomalous landforms on Mars can be attributed to glaciation, including the action of ice and meltwater. Glacial landscapes are concentrated south of lat -33° and in the Northern Plains suggesting vast Austral and Boreal ice sheets. Crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in Martian history. Thus, Mars may have had a relatively warm, moist climate and dense atmosphere much later than previously believed.

@article{doi1011300091761319920200003agom23co2,
    author = "Kargel, Jeffrey S. and Strom, R. G.",
    title = "Ancient glaciation on Mars",
    year = "1992",
    journal = "Geology",
    abstract = "A large number of anomalous landforms on Mars can be attributed to glaciation, including the action of ice and meltwater. Glacial landscapes are concentrated south of lat -33° and in the Northern Plains suggesting vast Austral and Boreal ice sheets. Crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in Martian history. Thus, Mars may have had a relatively warm, moist climate and dense atmosphere much later than previously believed.",
    url = "https://doi.org/10.1130/0091-7613(1992)020<0003:agom>2.3.co;2",
    doi = "10.1130/0091-7613(1992)020<0003:agom>2.3.co;2",
    openalex = "W2028134116"
}

Past studies of the climatic behavior of water on Mars have universally assumed that the atmosphere is the sole pathway available for volatile exchange between the planet's crustal and polar reservoirs of H 2 O. However, if the planetary inventory of outgassed H 2 O exceeds the pore volume of the cryosphere by more than a few percent, then a subpermafrost groundwater system of global extent will necessarily result. The existence of such a system raises the possibility that subsurface transport may complement long‐term atmospheric exchange. In this paper, the hydrologic response of a water‐rich Mars to climate change and to the physical and thermal evolution of its crust is considered. The analysis assumes that the atmospheric leg of the planet's long‐term hydrologic cycle is reasonably described by current models of insolation‐driven exchange. Under the climatic conditions that have apparently prevailed throughout most of Martian geologic history, the thermal instability of ground ice at low‐ to mid‐latitudes has led to a net atmospheric transport of H 2 O from the “hot” equatorial region to the colder poles. Theoretical arguments and various lines of morphologic evidence suggest that this poleward flux of H 2 O has been episodically augmented by additional releases of water resulting from impacts, catastrophic floods, and volcanism. Given an initially ice‐saturated cryosphere, the deposition of material at the poles (or any other location on the planet's surface) will result in a situation where the local equilibrium depth to the melting isotherm has been exceeded, melting ice at the base of the cryosphere until thermodynamic equilibrium is once again established. The downward percolation of basal meltwater into the global aquifer will result in the rise of the local water table in the form of a groundwater mound. Given geologically reasonable values of large‐scale crustal permeability (i.e., ≳ 10 −2 darcies), the gradient in hydraulic head created by the presence of the mound could then drive the equatorward flow of a significant volume of groundwater (≳ 10 8 km 3) over the course of Martian geologic history. At temperate and equatorial latitudes, the presence of a geothermal gradient will then result in a net discharge of the system as water vapor is thermally pumped from the higher temperature (higher vapor pressure) depths to the colder (lower vapor pressure) near‐surface crust. By this process, a gradient as small as 15 K km−1 could drive the vertical transport of 1 km of water to the freezing front at the base of the cryosphere every 10 6 –10 7 years, or the equivalent of ∼10 2 –10 3 km of water over the course of Martian geologic history. In this manner, much of the H 2 O that has been lost from the crust by the sublimation of equatorial ground ice, impacts, and catastrophic floods may ultimately be replenished. The validity of this analysis is supported by a detailed review of relevant spacecraft data, discussions of lunar and terrestrial analogs, and the use of well‐established hydrologic models. Among the additional topics discussed are the thermal and hydrologic properties of the crust, the potential distribution of ground ice and groundwater, the thermal evolution of the early cryosphere, the recharge of the valley networks and outflow channels, the polar mass balance, and a review of several important processes that are likely to drive the large‐scale vertical and horizontal transport of H 2 O beneath the Martian surface. Given a geologically reasonable description of the crust, and an outgassed inventory of water that exceeds the pore volume of the cryosphere by just a few percent, basic physics suggests that the hydrologic model described here will naturally evolve. If so, subsurface transport has likely played an important role in the geomorphic evolution of the Martian surface and the long‐term cycling of H 2 O between the atmosphere, polar caps, and near‐surface crust.

@article{doi10102993je00225,
    author = "Clifford, Stephen M.",
    title = "A model for the hydrologic and climatic behavior of water on Mars",
    year = "1993",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Past studies of the climatic behavior of water on Mars have universally assumed that the atmosphere is the sole pathway available for volatile exchange between the planet's crustal and polar reservoirs of H 2 O. However, if the planetary inventory of outgassed H 2 O exceeds the pore volume of the cryosphere by more than a few percent, then a subpermafrost groundwater system of global extent will necessarily result. The existence of such a system raises the possibility that subsurface transport may complement long‐term atmospheric exchange. In this paper, the hydrologic response of a water‐rich Mars to climate change and to the physical and thermal evolution of its crust is considered. The analysis assumes that the atmospheric leg of the planet's long‐term hydrologic cycle is reasonably described by current models of insolation‐driven exchange. Under the climatic conditions that have apparently prevailed throughout most of Martian geologic history, the thermal instability of ground ice at low‐ to mid‐latitudes has led to a net atmospheric transport of H 2 O from the “hot” equatorial region to the colder poles. Theoretical arguments and various lines of morphologic evidence suggest that this poleward flux of H 2 O has been episodically augmented by additional releases of water resulting from impacts, catastrophic floods, and volcanism. Given an initially ice‐saturated cryosphere, the deposition of material at the poles (or any other location on the planet's surface) will result in a situation where the local equilibrium depth to the melting isotherm has been exceeded, melting ice at the base of the cryosphere until thermodynamic equilibrium is once again established. The downward percolation of basal meltwater into the global aquifer will result in the rise of the local water table in the form of a groundwater mound. Given geologically reasonable values of large‐scale crustal permeability (i.e., ≳ 10 −2 darcies), the gradient in hydraulic head created by the presence of the mound could then drive the equatorward flow of a significant volume of groundwater (≳ 10 8 km 3) over the course of Martian geologic history. At temperate and equatorial latitudes, the presence of a geothermal gradient will then result in a net discharge of the system as water vapor is thermally pumped from the higher temperature (higher vapor pressure) depths to the colder (lower vapor pressure) near‐surface crust. By this process, a gradient as small as 15 K km−1 could drive the vertical transport of 1 km of water to the freezing front at the base of the cryosphere every 10 6 –10 7 years, or the equivalent of ∼10 2 –10 3 km of water over the course of Martian geologic history. In this manner, much of the H 2 O that has been lost from the crust by the sublimation of equatorial ground ice, impacts, and catastrophic floods may ultimately be replenished. The validity of this analysis is supported by a detailed review of relevant spacecraft data, discussions of lunar and terrestrial analogs, and the use of well‐established hydrologic models. Among the additional topics discussed are the thermal and hydrologic properties of the crust, the potential distribution of ground ice and groundwater, the thermal evolution of the early cryosphere, the recharge of the valley networks and outflow channels, the polar mass balance, and a review of several important processes that are likely to drive the large‐scale vertical and horizontal transport of H 2 O beneath the Martian surface. Given a geologically reasonable description of the crust, and an outgassed inventory of water that exceeds the pore volume of the cryosphere by just a few percent, basic physics suggests that the hydrologic model described here will naturally evolve. If so, subsurface transport has likely played an important role in the geomorphic evolution of the Martian surface and the long‐term cycling of H 2 O between the atmosphere, polar caps, and near‐surface crust.",
    url = "https://doi.org/10.1029/93je00225",
    doi = "10.1029/93je00225",
    openalex = "W2170615758",
    references = "doi1010160016703789901506, doi1010160734743x87900698, doi1010291998wr900047, doi101029jb085ib11p06248, doi101029jb091ib13p0e139, doi101029jz065i004p01083, doi101029jz066i007p02199, doi101029jz068i016p04795, doi101029tr038i002p00222, doi101038202526a0, doi101038352589a0, doi10113000167606195970115rofpim20co2, openalexw2045435453, openalexw2070611029, openalexw2139291338"
}

Abstract— The SNC meteorites are thought to be igneous martian rocks, based on their young crystallization ages and a close match between the composition of gases implanted in them during shock and the atmosphere of Mars. A related meteorite, ALH84001, may be older and thus may represent ancient martian crust. These petrologically diverse basalts and ultramafic rocks are mostly cumulates, but their parent magmas share geochemical and radiogenic isotopic characteristics that suggest they may have formed by remelting the same mantle source region at different times. Information and inferences about martian geology drawn from these samples include the following: Planetary differentiation occurred early at ∼4.5 Ga, probably concurrently with accretion. The martian mantle contains different abundances of moderately volatile and siderophile elements and is more Fe‐rich than that of the Earth, which has implications for its mineralogy, density, and origin. The estimated core composition has a S abundance near the threshold value for inner core solidification. The former presence of a core dynamo may be suggested by remanent magnetization in SNC meteorites, although these rocks may have been magnetized during shock. The mineralogy of martian surface units, inferred from reflectance spectra, matches that of basaltic shergottites, but SNC lithologies thought to have crystallized in the subsurface are not presently recognized. The rheological properties of martian magmas are more accurately derived from these meteorites than from observations of martian flow morphology, although the sampled range of magma compositions is limited. Estimates of planetary water abundance and the amount of outgassed water based on these meteorites are contradictory but overlap estimates based on geological observations and atmospheric measurements. Stable isotope measurements indicate that the martian hydrosphere experienced only limited exchange with the lithosphere, but it is in isotopic equilibrium with the atmosphere and has been since 1.3 Ga. The isotopically heavy atmosphere/hydrosphere composition deduced from these rocks reflects a loss process more severe than current atmospheric evolution models, and the occurrence of carbonates in SNC meteorites suggests that they, rather than scapolite or hydrous carbonates, are the major crustal sink for CO 2. Weathering products in SNC meteorites support the idea of limited alteration of the lithosphere by small volumes of saline, CO 2 ‐bearing water. Atmospheric composition and evolution are further constrained by noble gases in these meteorites, although Xe and Kr isotopes suggest different origins for the atmosphere. Planetary ejection of these rocks has promoted an advance in the understanding of impact physics, which has been accomplished by a model involving spallation during large cratering events. Ejection of all the SNC meteorites (except ALH84001) in one or two events may provide a plausible solution to most constraints imposed by chronology, geochemistry, and cosmic ray exposure, although problems remain with this scenario; ALH84001 may represent older martian crust sampled during a separate impact.

@article{doi101111j194551001994tb01092x,
    author = "McSween, H. Y.",
    title = "What we have learned about Mars from SNC meteorites",
    year = "1994",
    journal = "Meteoritics",
    abstract = "Abstract— The SNC meteorites are thought to be igneous martian rocks, based on their young crystallization ages and a close match between the composition of gases implanted in them during shock and the atmosphere of Mars. A related meteorite, ALH84001, may be older and thus may represent ancient martian crust. These petrologically diverse basalts and ultramafic rocks are mostly cumulates, but their parent magmas share geochemical and radiogenic isotopic characteristics that suggest they may have formed by remelting the same mantle source region at different times. Information and inferences about martian geology drawn from these samples include the following: Planetary differentiation occurred early at ∼4.5 Ga, probably concurrently with accretion. The martian mantle contains different abundances of moderately volatile and siderophile elements and is more Fe‐rich than that of the Earth, which has implications for its mineralogy, density, and origin. The estimated core composition has a S abundance near the threshold value for inner core solidification. The former presence of a core dynamo may be suggested by remanent magnetization in SNC meteorites, although these rocks may have been magnetized during shock. The mineralogy of martian surface units, inferred from reflectance spectra, matches that of basaltic shergottites, but SNC lithologies thought to have crystallized in the subsurface are not presently recognized. The rheological properties of martian magmas are more accurately derived from these meteorites than from observations of martian flow morphology, although the sampled range of magma compositions is limited. Estimates of planetary water abundance and the amount of outgassed water based on these meteorites are contradictory but overlap estimates based on geological observations and atmospheric measurements. Stable isotope measurements indicate that the martian hydrosphere experienced only limited exchange with the lithosphere, but it is in isotopic equilibrium with the atmosphere and has been since 1.3 Ga. The isotopically heavy atmosphere/hydrosphere composition deduced from these rocks reflects a loss process more severe than current atmospheric evolution models, and the occurrence of carbonates in SNC meteorites suggests that they, rather than scapolite or hydrous carbonates, are the major crustal sink for CO 2. Weathering products in SNC meteorites support the idea of limited alteration of the lithosphere by small volumes of saline, CO 2 ‐bearing water. Atmospheric composition and evolution are further constrained by noble gases in these meteorites, although Xe and Kr isotopes suggest different origins for the atmosphere. Planetary ejection of these rocks has promoted an advance in the understanding of impact physics, which has been accomplished by a model involving spallation during large cratering events. Ejection of all the SNC meteorites (except ALH84001) in one or two events may provide a plausible solution to most constraints imposed by chronology, geochemistry, and cosmic ray exposure, although problems remain with this scenario; ALH84001 may represent older martian crust sampled during a separate impact.",
    url = "https://doi.org/10.1111/j.1945-5100.1994.tb01092.x",
    doi = "10.1111/j.1945-5100.1994.tb01092.x",
    openalex = "W2132738826",
    references = "doi10102993je00225, doi101126science2214611651"
}

Abstract Mars has always held a special interest because of the possibility that life may have existed there, and its water history is crucial to understanding its geology, climatology, and biology. Moreover, recent studies in molecular phylogeny suggest that volcanic hot springs, which may have been common in early Mars, are also the most likely point of origin for life on Earth. In this book, Dr. Carr explores the history of water on Mars, including evidence that liquid water was once abundant at the planet’s surface; ways in which the climate might have changed to accommodate liquid water; and what an abundance of water implies for the formation of Mars and other planets, including Earth. The book’s argument rests on interpretation of data acquired on Viking missions, and on information from meteorites, found on Earth, that almost certainly originated on Mars. Because liquid water is universally regarded as essential for life, the water story has particular biological significance, with important implications for the future exploration of the planet, and should be a valuable study for geologists and planetary scientists.

@book{doi101093oso97801950993860010001,
    author = "Carr, M. H.",
    title = "Water On Mars",
    year = "1996",
    abstract = "Abstract Mars has always held a special interest because of the possibility that life may have existed there, and its water history is crucial to understanding its geology, climatology, and biology. Moreover, recent studies in molecular phylogeny suggest that volcanic hot springs, which may have been common in early Mars, are also the most likely point of origin for life on Earth. In this book, Dr. Carr explores the history of water on Mars, including evidence that liquid water was once abundant at the planet’s surface; ways in which the climate might have changed to accommodate liquid water; and what an abundance of water implies for the formation of Mars and other planets, including Earth. The book’s argument rests on interpretation of data acquired on Viking missions, and on information from meteorites, found on Earth, that almost certainly originated on Mars. Because liquid water is universally regarded as essential for life, the water story has particular biological significance, with important implications for the future exploration of the planet, and should be a valuable study for geologists and planetary scientists.",
    url = "https://doi.org/10.1093/oso/9780195099386.001.0001",
    doi = "10.1093/oso/9780195099386.001.0001",
    openalex = "W4388314709"
}

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

@article{doi101126science2735277924,
    author = "McKay, D. S. and Gibson, E. K. and Thomas-Keprta, K. L. and Vali, Hojatollah and Romanek, Christopher S. and Clemett, S. J. and Chillier, Xavier D. F. and Maechling, Claude R. and Zare, Richard N.",
    title = "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001",
    year = "1996",
    journal = "Science",
    abstract = "Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.",
    url = "https://doi.org/10.1126/science.273.5277.924",
    doi = "10.1126/science.273.5277.924",
    openalex = "W1968713120",
    references = "doi1010079781468427578, doi10100797814684275788, doi1010079783642964466, doi1010160016703778901825, doi101017cbo9780511601064, doi101038228923a0, doi101038330252a0, doi101126science2705235450, doi101144gsjgs13360637, doi101146annurevmi48100194001523"
}

Estimates of the amount of water outgassed from Mars, based on the composition of the atmosphere, range from 6 to 160 m, as compared with 3 km for the Earth. In contrast, large flood features, valley networks, and several indicators of ground ice suggest that at least 500 m of water have outgassed. The two sets of estimates may be reconciled if early in its history, Mars lost part of its atmosphere by impact erosion and hydrodynamic escape.

@book{openalexw2045435453,
    author = "Carr, M. H.",
    title = "Water on Mars",
    year = "1996",
    abstract = "Estimates of the amount of water outgassed from Mars, based on the composition of the atmosphere, range from 6 to 160 m, as compared with 3 km for the Earth. In contrast, large flood features, valley networks, and several indicators of ground ice suggest that at least 500 m of water have outgassed. The two sets of estimates may be reconciled if early in its history, Mars lost part of its atmosphere by impact erosion and hydrodynamic escape.",
    url = "https://openalex.org/W2045435453",
    openalex = "W2045435453",
    references = "doi1010079781461261674, doi1010160016703779901807, doi1010160019103574901018, doi101029jb084ib06p02995, doi101029js082i028p04635, doi101098rsta19810203, doi101126science1533732136, doi101126science2214611651, doi101126science2314735249, openalexw2996298354"
}

@article{doi101016s0032063397001864,
    author = "Leweling, Martin and Spohn, Tilman",
    title = "Mars: a magnetic field due to thermoremanence?",
    year = "1997",
    journal = "Planetary and Space Science",
    url = "https://doi.org/10.1016/s0032-0633(97)00186-4",
    doi = "10.1016/s0032-0633(97)00186-4",
    openalex = "W2038539835"
}

Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica, implying differentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than approximately 1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free.

@article{doi101126science27853441743,
    author = "Golombek, M. P. and Cook, Richard A. and Economou, T. and Folkner, W. M. and Haldemann, A. F. C. and Kallemeyn, P. H. and Knudsen, J. M. and Manning, Robert M. and Moore, H. J. and Parker, T. J. and Rieder, R. and Schofield, J. T. and Smith, Peter H. and Vaughan, R. M.",
    title = "Overview of the Mars Pathfinder Mission and Assessment of Landing Site Predictions",
    year = "1997",
    journal = "Science",
    abstract = "Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica, implying differentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than approximately 1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free.",
    url = "https://doi.org/10.1126/science.278.5344.1743",
    doi = "10.1126/science.278.5344.1743",
    openalex = "W2128016423"
}

Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between approximately 100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian highlands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch (approximately 4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 x 10(17) ampere-meter2 in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.

@article{doi101126science2845415790,
    author = "Acuña, M. H. and Connerney, J. E. P. and F., N. and Ness and Lin, R. P. and Mitchell, David and Carlson, C. W. and McFadden, J. P. and Anderson, K. A. and Rème, H. and Mazelle, C. and Vignes, D. and Wasilewski, P. J. and Cloutier, P. A.",
    title = "Global Distribution of Crustal Magnetization Discovered by the Mars Global Surveyor MAG/ER Experiment",
    year = "1999",
    journal = "Science",
    abstract = "Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between approximately 100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian highlands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch (approximately 4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 x 10(17) ampere-meter2 in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.",
    url = "https://doi.org/10.1126/science.284.5415.790",
    doi = "10.1126/science.284.5415.790",
    openalex = "W2138964904",
    references = "doi1010160032063391901303, doi101016s0032063397001864, doi10102991rg00066, doi10102992je00344, doi101029gl015i003p00229, doi101029jb092ib11p11584, doi101029jb095ib08p12595, doi101038309138a0, doi101111j1365246x1975tb05859x, doi101126science2845415794"
}

The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit, obtained vector magnetic field measurements above the surface of Mars (altitudes >100 kilometers). Crustal magnetization, mainly confined to the most ancient, heavily cratered martian highlands, is frequently organized in east-west-trending linear features, the longest extending over 2000 kilometers. Crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity were found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale. They may be a relic of an era of plate tectonics on Mars.

@article{doi101126science2845415794,
    author = "Connerney, J. E. P. and Acuña, M. H. and Wasilewski, P. J. and Ness, N. F. and Rème, H. and Mazelle, C. and Vignes, D. and Lin, R. P. and Mitchell, D. L. and Cloutier, P. A.",
    title = "Magnetic Lineations in the Ancient Crust of Mars",
    year = "1999",
    journal = "Science",
    abstract = "The Mars Global Surveyor spacecraft, in a highly elliptical polar orbit, obtained vector magnetic field measurements above the surface of Mars (altitudes >100 kilometers). Crustal magnetization, mainly confined to the most ancient, heavily cratered martian highlands, is frequently organized in east-west-trending linear features, the longest extending over 2000 kilometers. Crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude. Groups of quasi-parallel linear features of alternating magnetic polarity were found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale. They may be a relic of an era of plate tectonics on Mars.",
    url = "https://doi.org/10.1126/science.284.5415.794",
    doi = "10.1126/science.284.5415.794",
    openalex = "W2042409585",
    references = "doi101126science15437531164"
}

Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.

@article{doi101126science28454191495,
    author = "Smith, David E. and Zuber, M. T. and Solomon, Sean C. and Phillips, R. J. and Head, J. W. and Garvin, J. B. and Banerdt, W. B. and Muhleman, D. O. and Pettengill, G. H. and Neumann, G. A. and Lemoine, F. G. and Abshire, James B. and Aharonson, O. and David, Cristiam and Brown and Hauck, S. A. and Ivanov, A. B. and McGovern, P. J. and Zwally, H. Jay and Duxbury, T.",
    title = "The Global Topography of Mars and Implications for Surface Evolution",
    year = "1999",
    journal = "Science",
    abstract = "Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.",
    url = "https://doi.org/10.1126/science.284.5419.1495",
    doi = "10.1126/science.284.5419.1495",
    openalex = "W2147284262",
    references = "doi1010160019103589900274, doi10102992je00341, doi10102993je00225, doi10102993je00618, doi101029jb086ib05p03951, doi101038352589a0, doi101093oso97801950993860010001, doi101126science26651921839, doi101126science2845415794, doi1011300091761319920200003agom23co2"
}

@article{doi101006icar20006503,
    author = "Mellon, M. T.",
    title = "High-Resolution Thermal Inertia Mapping from the Mars Global Surveyor Thermal Emission Spectrometer",
    year = "2000",
    journal = "Icarus",
    url = "https://doi.org/10.1006/icar.2000.6503",
    doi = "10.1006/icar.2000.6503",
    openalex = "W1997889228",
    references = "doi101029js082i028p04249"
}

The Thermal Emission Spectrometer (TES) instrument on the Mars Global Surveyor (MGS) mission has discovered a remarkable accumulation of crystalline hematite (α‐Fe 2 O 3) that covers an area with very sharp boundaries approximately 350 by 350–750 km in size centered near 2°S latitude between 0° and 5°W longitude (Sinus Meridiani). Crystalline hematite is uniquely identified by the presence of fundamental vibrational absorption features centered near 300, 450, and >525 cm −1 and by the absence of silicate fundamentals in the 1000 cm −1 region. Spectral features resulting from atmospheric CO 2, dust, and water ice were removed using a radiative transfer model. The spectral properties unique to Sinus Meridiani were emphasized by removing the average spectrum of the surrounding region. The depth and shape of the hematite fundamental bands show that the hematite is crystalline and relatively coarse grained (>5–10 μm). Diameters up to and greater than hundreds of micrometers are permitted within the instrumental noise and natural variability of hematite spectra. Hematite particles 30 μm diameter) to 40–60% (10 μm diameter). The hematite in Sinus Meridiani is thus distinct from the fine‐grained (diameter <5–10 μm), red, crystalline hematite considered, on the basis of visible, near‐IR data, to be a minor spectral component in Martian bright regions like Olympus‐Amazonis. Sinus Meridiani hematite is closely associated with a smooth, layered, friable surface that is interpreted to be sedimentary in origin. This material may be the uppermost surface in the region, indicating that it might be a late stage sedimentary unit or a layered portion of the heavily cratered plains units. We consider five possible mechanisms for the formation of coarse‐grained, crystalline hematite. These processes fall into two classes depending on whether they require a significant amount of near‐surface water: the first is chemical precipitation that includes origin by (1) precipitation from standing, oxygenated, Fe‐rich water (oxide iron formations), (2) precipitation from Fe‐rich hydrothermal fluids, (3) low‐temperature dissolution and precipitation through mobile ground water leaching, and (4) formation of surface coatings, and the second is thermal oxidation of magnetite‐rich lavas. Weathering and alteration processes, which produce nanophase and red hematite, are not consistent with the coarse, crystalline hematite observed in Sinus Meridiani. We prefer chemical precipitation models and favor precipitation from Fe‐rich water on the basis of the probable association with sedimentary materials, large geographic size, distance from a regional heat source, and lack of evidence for extensive groundwater processes elsewhere on Mars. The TES results thus provide mineralogic evidence for probable large‐scale water interactions. The Sinus Meridiani region may be an ideal candidate for future landed missions searching for biotic and prebiotic environments, and the physical characteristics of this site satisfy all of the engineering requirements for the missions currently planned.

@article{doi1010291999je001093,
    author = "Christensen, P. R. and Bandfield, J. L. and Clark, R. N. and Edgett, K. S. and Hamilton, V. E. and Hoefen, Todd M. and Kieffer, H. H. and Kuzmin, R. O. and Lane, M. D. and Malin, M. C. and Morris, R. V. and Pearl, J. C. and Pearson, Robert L. and Roush, T. L. and Ruff, S. W. and Smith, M. D.",
    title = "Detection of crystalline hematite mineralization on Mars by the Thermal Emission Spectrometer: Evidence for near‐surface water",
    year = "2000",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Thermal Emission Spectrometer (TES) instrument on the Mars Global Surveyor (MGS) mission has discovered a remarkable accumulation of crystalline hematite (α‐Fe 2 O 3) that covers an area with very sharp boundaries approximately 350 by 350–750 km in size centered near 2°S latitude between 0° and 5°W longitude (Sinus Meridiani). Crystalline hematite is uniquely identified by the presence of fundamental vibrational absorption features centered near 300, 450, and >525 cm −1 and by the absence of silicate fundamentals in the 1000 cm −1 region. Spectral features resulting from atmospheric CO 2, dust, and water ice were removed using a radiative transfer model. The spectral properties unique to Sinus Meridiani were emphasized by removing the average spectrum of the surrounding region. The depth and shape of the hematite fundamental bands show that the hematite is crystalline and relatively coarse grained (>5–10 μm). Diameters up to and greater than hundreds of micrometers are permitted within the instrumental noise and natural variability of hematite spectra. Hematite particles 30 μm diameter) to 40–60\% (10 μm diameter). The hematite in Sinus Meridiani is thus distinct from the fine‐grained (diameter <5–10 μm), red, crystalline hematite considered, on the basis of visible, near‐IR data, to be a minor spectral component in Martian bright regions like Olympus‐Amazonis. Sinus Meridiani hematite is closely associated with a smooth, layered, friable surface that is interpreted to be sedimentary in origin. This material may be the uppermost surface in the region, indicating that it might be a late stage sedimentary unit or a layered portion of the heavily cratered plains units. We consider five possible mechanisms for the formation of coarse‐grained, crystalline hematite. These processes fall into two classes depending on whether they require a significant amount of near‐surface water: the first is chemical precipitation that includes origin by (1) precipitation from standing, oxygenated, Fe‐rich water (oxide iron formations), (2) precipitation from Fe‐rich hydrothermal fluids, (3) low‐temperature dissolution and precipitation through mobile ground water leaching, and (4) formation of surface coatings, and the second is thermal oxidation of magnetite‐rich lavas. Weathering and alteration processes, which produce nanophase and red hematite, are not consistent with the coarse, crystalline hematite observed in Sinus Meridiani. We prefer chemical precipitation models and favor precipitation from Fe‐rich water on the basis of the probable association with sedimentary materials, large geographic size, distance from a regional heat source, and lack of evidence for extensive groundwater processes elsewhere on Mars. The TES results thus provide mineralogic evidence for probable large‐scale water interactions. The Sinus Meridiani region may be an ideal candidate for future landed missions searching for biotic and prebiotic environments, and the physical characteristics of this site satisfy all of the engineering requirements for the missions currently planned.",
    url = "https://doi.org/10.1029/1999je001093",
    doi = "10.1029/1999je001093",
    openalex = "W2159827469"
}

Topography and gravity measured by the Mars Global Surveyor have enabled determination of the global crust and upper mantle structure of Mars. The planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy: a region of crust that thins progressively from south to north and encompasses much of the southern highlands and Tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and Arabia Terra. The strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history. The thickness of the elastic lithosphere increases with time of loading in the northern plains and Tharsis. The northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing.

@article{doi101126science28754591788,
    author = "Zuber, M. T. and Solomon, Sean C. and Phillips, R. J. and Smith, David E. and Tyler, G. L. and Aharonson, O. and Balmino, G. and Banerdt, W. B. and Head, J. W. and Johnson, C. L. and Lemoine, F. G. and McGovern, P. J. and Neumann, G. A. and Rowlands, D. D. and Zhong, Shijie",
    title = "Internal Structure and Early Thermal Evolution of Mars from Mars Global Surveyor Topography and Gravity",
    year = "2000",
    journal = "Science",
    abstract = "Topography and gravity measured by the Mars Global Surveyor have enabled determination of the global crust and upper mantle structure of Mars. The planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy: a region of crust that thins progressively from south to north and encompasses much of the southern highlands and Tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and Arabia Terra. The strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history. The thickness of the elastic lithosphere increases with time of loading in the northern plains and Tharsis. The northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing.",
    url = "https://doi.org/10.1126/science.287.5459.1788",
    doi = "10.1126/science.287.5459.1788",
    openalex = "W2104652753",
    references = "doi101029jb090ib14p12623, doi101126science2845415790, doi101126science28454191495"
}

Relatively young landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the martian surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed landforms or cross-cutting features, including impact craters, small polygons, and eolian dunes. The limited size and geographic distribution of the features argue for constrained source reservoirs.

@article{doi101126science28854752330,
    author = "Malin, M. C. and Edgett, K. S.",
    title = "Evidence for Recent Groundwater Seepage and Surface Runoff on Mars",
    year = "2000",
    journal = "Science",
    abstract = "Relatively young landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the martian surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed landforms or cross-cutting features, including impact craters, small polygons, and eolian dunes. The limited size and geographic distribution of the features argue for constrained source reservoirs.",
    url = "https://doi.org/10.1126/science.288.5475.2330",
    doi = "10.1126/science.288.5475.2330",
    openalex = "W2037372977",
    references = "doi1010160019103574901018, doi1010160033589476900375, doi101016s0169555x9700024x, doi10103817551, doi101093oso97801950993860010001, doi101126science27853441743, doi101126science28854752335, doi10113000167606195667823copgar20co2, doi10113000167606197586593com20co2, doi10113000167606198596203spatdo20co2"
}

Layered and massive outcrops on Mars, some as thick as 4 kilometers, display the geomorphic attributes and stratigraphic relations of sedimentary rock. Repeated beds in some locations imply a dynamic depositional environment during early martian history. Subaerial (such as eolian, impact, and volcaniclastic) and subaqueous processes may have contributed to the formation of the layers. Affinity for impact craters suggests dominance of lacustrine deposition; alternatively, the materials were deposited in a dry, subaerial setting in which atmospheric density, and variations thereof mimic a subaqueous depositional environment. The source regions and transport paths for the materials are not preserved.

@article{doi101126science29054981927,
    author = "Malin, M. C. and Edgett, K. S.",
    title = "Sedimentary Rocks of Early Mars",
    year = "2000",
    journal = "Science",
    abstract = "Layered and massive outcrops on Mars, some as thick as 4 kilometers, display the geomorphic attributes and stratigraphic relations of sedimentary rock. Repeated beds in some locations imply a dynamic depositional environment during early martian history. Subaerial (such as eolian, impact, and volcaniclastic) and subaqueous processes may have contributed to the formation of the layers. Affinity for impact craters suggests dominance of lacustrine deposition; alternatively, the materials were deposited in a dry, subaerial setting in which atmospheric density, and variations thereof mimic a subaqueous depositional environment. The source regions and transport paths for the materials are not preserved.",
    url = "https://doi.org/10.1126/science.290.5498.1927",
    doi = "10.1126/science.290.5498.1927",
    openalex = "W1983027048",
    references = "doi101006icar19996191, doi1010079783642748646, doi1010160019103587901473, doi1010291998je000540, doi1010291999je001093, doi101029jb091ib13p0e139, doi101086622910, doi101086626936, doi101126science1533732136, doi10113000167606197586593com20co2"
}

@incollection{doi10100797894017103504,
    author = "Ivanov, B. A.",
    title = "Mars/Moon Cratering Rate Ratio Estimates",
    year = "2001",
    booktitle = "Space sciences series of ISSI",
    url = "https://doi.org/10.1007/978-94-017-1035-0\_4",
    doi = "10.1007/978-94-017-1035-0\_4",
    openalex = "W1664327713",
    references = "doi101006icar19975713, doi10100797894017103503, doi10100797894017103506, doi1010160734743x87900698, doi101029jb090is02p0c828, doi101111j194551001992tb01074x, doi101126science2775323197, doi101126science28854742190, doi101146annurevearth271385, doi102307jctv1v3gr3r15, openalexw1648269713, openalexw1655381311"
}

@incollection{doi10100797894017103506,
    author = "Hartmann, W. K. and Neukum, G.",
    title = "Cratering Chronology and the Evolution of Mars",
    year = "2001",
    booktitle = "Space sciences series of ISSI",
    url = "https://doi.org/10.1007/978-94-017-1035-0\_6",
    doi = "10.1007/978-94-017-1035-0\_6",
    openalex = "W2115280605",
    references = "doi10100797894017103502, doi10100797894017103503, doi10100797894017103504, doi10100797894017103505, doi101029jb091ib13p0e139, doi101126science2214611651, doi101126science28854752330, doi101126science29054981927, doi105860choice330281, openalexw2139291338"
}

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064‐μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ∼1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1×2 km 2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100‐m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100‐m‐scale surface roughness and 1.064‐μm reflectivity with an accuracy of 5% have also been obtained.

@article{doi1010292000je001364,
    author = "Smith, David E. and Zuber, M. T. and Frey, Herbert and Garvin, J. B. and Head, J. W. and Muhleman, D. O. and Pettengill, G. H. and Phillips, R. J. and Solomon, Sean C. and Zwally, H. Jay and Banerdt, W. B. and Duxbury, T. and Golombek, M. P. and Lemoine, F. G. and Neumann, G. A. and Rowlands, D. D. and Aharonson, O. and Ford, P. G. and Ivanov, A. B. and Johnson, C. L. and McGovern, P. J. and Abshire, James B. and Afzal, Robert S. and Sun, Xiaoli",
    title = "Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars",
    year = "2001",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064‐μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ∼1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1×2 km 2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100‐m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100‐m‐scale surface roughness and 1.064‐μm reflectivity with an accuracy of 5\% have also been obtained.",
    url = "https://doi.org/10.1029/2000je001364",
    doi = "10.1029/2000je001364",
    openalex = "W2045323482",
    references = "doi1010160016703789901506, doi1010292000je001370, doi10102993je00225, doi101029js082i028p04249, doi101038352589a0, doi101126science2845415790, doi101126science28454191495, doi101126science28854752330, doi10119011442837, openalexw2139291338"
}

The Thermal Emission Spectrometer (TES) investigation on Mars Global Surveyor (MGS) is aimed at determining (1) the composition of surface minerals, rocks, and ices; (2) the temperature and dynamics of the atmosphere; (3) the properties of the atmospheric aerosols and clouds; (4) the nature of the polar regions; and (5) the thermophysical properties of the surface materials. These objectives are met using an infrared (5.8‐ to 50‐μm) interferometric spectrometer, along with broadband thermal (5.1‐ to 150‐μm) and visible/near‐IR (0.3‐ to 2.9‐μm) radiometers. The MGS TES instrument weighs 14.47 kg, consumes 10.6 W when operating, and is 23.6×35.5×40.0 cm in size. The TES data are calibrated to a 1‐σ precision of 2.5 −6 ×10 −8 W cm −2 sr −1 /cm −1, 1.6×10 −6 W cm −2 sr −1, and ∼0.5 K in the spectrometer, visible/near‐IR bolometer, and IR bolometer, respectively. These instrument subsections are calibrated to an absolute accuracy of ∼4×10 −8 W cm −2 sr −1 /cm −1 (0.5 K at 280 K), 1–2%, and ∼1–2 K, respectively. Global mapping of surface mineralogy at a spatial resolution of 3 km has shown the following: (1) The mineralogic composition of dark regions varies from basaltic, primarily plagioclase feldspar and clinopyroxene, in the ancient, southern highlands to andesitic, dominated by plagioclase feldspar and volcanic glass, in the younger northern plains. (2) Aqueous mineralization has produced gray, crystalline hematite in limited regions under ambient or hydrothermal conditions; these deposits are interpreted to be in‐place sedimentary rock formations and indicate that liquid water was stable near the surface for a long period of time. (3) There is no evidence for large‐scale (tens of kilometers) occurrences of moderate‐grained (>50‐μm) carbonates exposed at the surface at a detection limit of ∼10%. (4) Unweathered volcanic minerals dominate the spectral properties of dark regions, and weathering products, such as clays, have not been observed anywhere above a detection limit of ∼10%; this lack of evidence for chemical weathering indicates a geologic history dominated by a cold, dry climate in which mechanical, rather than chemical, weathering was the significant form of erosion and sediment production. (5) There is no conclusive evidence for sulfate minerals at a detection limit of ∼15%. The polar region has been studied with the following major conclusions: (1) Condensed CO 2 has three distinct end‐members, from fine‐grained crystals to slab ice. (2) The growth and retreat of the polar caps observed by MGS is virtually the same as observed by Viking 12 Martian years ago. (3) Unique regions have been identified that appear to differ primarily in the grain size of CO 2; one south polar region appears to remain as black slab CO 2 ice throughout its sublimation. (4) Regional atmospheric dust is common in localized and regional dust storms around the margin and interior of the southern cap. Analysis of the thermophysical properties of the surface shows that (1) the spatial pattern of albedo has changed since Viking observations, (2) a unique cluster of surface materials with intermediate inertia and albedo occurs that is distinct from the previously identified low‐inertia/bright and high‐inertia/dark surfaces, and (3) localized patches of high‐inertia material have been found in topographic lows and may have been formed by a unique set of aeolian, fluvial, or erosional processes or may be exposed bedrock.

@article{doi1010292000je001370,
    author = "Christensen, P. R. and Bandfield, J. L. and Hamilton, V. E. and Ruff, S. W. and Kieffer, H. H. and Titus, T. N. and Malin, M. C. and Morris, R. V. and Lane, M. D. and Clark, R. L. and Jakosky, B. M. and Mellon, M. T. and Pearl, J. C. and Conrath, B. J. and Smith, M. D. and Clancy, R. T. and Kuzmin, R. O. and Roush, T. L. and Mehall, G. and Gorelick, Noel and Bender, K. and Murray, K. and Dason, S. and Greene, E. P. and Silverman, S. and Greenfield, M.I.",
    title = "Mars Global Surveyor Thermal Emission Spectrometer experiment: Investigation description and surface science results",
    year = "2001",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Thermal Emission Spectrometer (TES) investigation on Mars Global Surveyor (MGS) is aimed at determining (1) the composition of surface minerals, rocks, and ices; (2) the temperature and dynamics of the atmosphere; (3) the properties of the atmospheric aerosols and clouds; (4) the nature of the polar regions; and (5) the thermophysical properties of the surface materials. These objectives are met using an infrared (5.8‐ to 50‐μm) interferometric spectrometer, along with broadband thermal (5.1‐ to 150‐μm) and visible/near‐IR (0.3‐ to 2.9‐μm) radiometers. The MGS TES instrument weighs 14.47 kg, consumes 10.6 W when operating, and is 23.6×35.5×40.0 cm in size. The TES data are calibrated to a 1‐σ precision of 2.5 −6 ×10 −8 W cm −2 sr −1 /cm −1, 1.6×10 −6 W cm −2 sr −1, and ∼0.5 K in the spectrometer, visible/near‐IR bolometer, and IR bolometer, respectively. These instrument subsections are calibrated to an absolute accuracy of ∼4×10 −8 W cm −2 sr −1 /cm −1 (0.5 K at 280 K), 1–2\%, and ∼1–2 K, respectively. Global mapping of surface mineralogy at a spatial resolution of 3 km has shown the following: (1) The mineralogic composition of dark regions varies from basaltic, primarily plagioclase feldspar and clinopyroxene, in the ancient, southern highlands to andesitic, dominated by plagioclase feldspar and volcanic glass, in the younger northern plains. (2) Aqueous mineralization has produced gray, crystalline hematite in limited regions under ambient or hydrothermal conditions; these deposits are interpreted to be in‐place sedimentary rock formations and indicate that liquid water was stable near the surface for a long period of time. (3) There is no evidence for large‐scale (tens of kilometers) occurrences of moderate‐grained (>50‐μm) carbonates exposed at the surface at a detection limit of ∼10\%. (4) Unweathered volcanic minerals dominate the spectral properties of dark regions, and weathering products, such as clays, have not been observed anywhere above a detection limit of ∼10\%; this lack of evidence for chemical weathering indicates a geologic history dominated by a cold, dry climate in which mechanical, rather than chemical, weathering was the significant form of erosion and sediment production. (5) There is no conclusive evidence for sulfate minerals at a detection limit of ∼15\%. The polar region has been studied with the following major conclusions: (1) Condensed CO 2 has three distinct end‐members, from fine‐grained crystals to slab ice. (2) The growth and retreat of the polar caps observed by MGS is virtually the same as observed by Viking 12 Martian years ago. (3) Unique regions have been identified that appear to differ primarily in the grain size of CO 2; one south polar region appears to remain as black slab CO 2 ice throughout its sublimation. (4) Regional atmospheric dust is common in localized and regional dust storms around the margin and interior of the southern cap. Analysis of the thermophysical properties of the surface shows that (1) the spatial pattern of albedo has changed since Viking observations, (2) a unique cluster of surface materials with intermediate inertia and albedo occurs that is distinct from the previously identified low‐inertia/bright and high‐inertia/dark surfaces, and (3) localized patches of high‐inertia material have been found in topographic lows and may have been formed by a unique set of aeolian, fluvial, or erosional processes or may be exposed bedrock.",
    url = "https://doi.org/10.1029/2000je001370",
    doi = "10.1029/2000je001370",
    openalex = "W2105924554",
    references = "doi101006icar20006503, doi1010160012825294900183, doi101029jb091ib08p08098, doi101029js082i028p04249, doi101038338487a0, doi101126science27853441771, doi101126science28754581626, doi10114912430134, doi101180mono4, doi101364ao23001206, openalexw2302969081"
}

More than 3 years of high‐resolution (1.5–20 m/pixel) photographic observations of the surface of Mars have dramatically changed our view of that planet. Among the most important observations and interpretations derived therefrom are that much of Mars, at least to depths of several kilometers, is layered; that substantial portions of the planet have experienced burial and subsequent exhumation; that layered and massive units, many kilometers thick, appear to reflect an ancient period of large‐scale erosion and deposition within what are now the ancient heavily cratered regions of Mars; and that processes previously unsuspected, including gully‐forming fluid action and burial and exhumation of large tracts of land, have operated within near‐contemporary times. These and many other attributes of the planet argue for a complex geology and complicated history.

@article{doi1010292000je001455,
    author = "Malin, M. C. and Edgett, K. S.",
    title = "Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission",
    year = "2001",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "More than 3 years of high‐resolution (1.5–20 m/pixel) photographic observations of the surface of Mars have dramatically changed our view of that planet. Among the most important observations and interpretations derived therefrom are that much of Mars, at least to depths of several kilometers, is layered; that substantial portions of the planet have experienced burial and subsequent exhumation; that layered and massive units, many kilometers thick, appear to reflect an ancient period of large‐scale erosion and deposition within what are now the ancient heavily cratered regions of Mars; and that processes previously unsuspected, including gully‐forming fluid action and burial and exhumation of large tracts of land, have operated within near‐contemporary times. These and many other attributes of the planet argue for a complex geology and complicated history.",
    url = "https://doi.org/10.1029/2000je001455",
    doi = "10.1029/2000je001455",
    openalex = "W2020905882",
    references = "doi1010079789400956827, doi101017cbo9780511573071, doi1010292000je001370, doi10102993je00225, doi101029jb091ib13p0e139, doi101038352589a0, doi101086622910, doi101126science28754581626, doi101126science28854752330, doi101126science29054981927"
}

@article{doi10103835084184,
    author = "Jakosky, B. M. and Phillips, R. J.",
    title = "Mars' volatile and climate history",
    year = "2001",
    journal = "Nature",
    url = "https://doi.org/10.1038/35084184",
    doi = "10.1038/35084184",
    openalex = "W1641814916",
    references = "doi101038338487a0"
}

@article{doi10103835086515,
    author = "Mustard, John F. and Cooper, Christopher D. and Rifkin, M. K.",
    title = "Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice",
    year = "2001",
    journal = "Nature",
    url = "https://doi.org/10.1038/35086515",
    doi = "10.1038/35086515",
    openalex = "W1983550241"
}

Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of approximately 3 x 10(8) cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough.

@article{doi101126science1058701,
    author = "Phillips, R. J. and Zuber, M. T. and Solomon, Sean C. and Golombek, M. P. and Jakosky, B. M. and Banerdt, W. B. and Smith, David E. and Williams, R. M. E. and Hynek, B. M. and Aharonson, O. and Hauck, S. A.",
    title = "Ancient Geodynamics and Global-Scale Hydrology on Mars",
    year = "2001",
    journal = "Science",
    abstract = "Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of approximately 3 x 10(8) cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough.",
    url = "https://doi.org/10.1126/science.1058701",
    doi = "10.1126/science.1058701",
    openalex = "W2096724893"
}

@article{doi101006icar20026921,
    author = "Burr, D. M. and Grier, J. A. and McEwen, A. S. and Keszthelyi, L.",
    title = "Repeated Aqueous Flooding from the Cerberus Fossae: Evidence for Very Recently Extant, Deep Groundwater on Mars",
    year = "2002",
    journal = "Icarus",
    url = "https://doi.org/10.1006/icar.2002.6921",
    doi = "10.1006/icar.2002.6921",
    openalex = "W1981827228",
    references = "doi101126science28854742190, doi103133pp596"
}

Valley networks provide compelling evidence that past geologic processes on Mars were different than those seen today. The generally accepted paradigm is that these features formed from groundwater circulation, which may have been driven by differential heating induced by magmatic intrusions, impact melt, or a higher primordial heat flux. Although such mechanisms may not require climatic conditions any different than today's, they fail to explain the large amount of recharge necessary for maintaining valley network systems, the spatial patterns of erosion, or how water became initially situated in the Martian regolith. In addition, there are no clear surface manifestations of any geothermal systems (e.g., mineral deposits or phreatic explosion craters). Finally, these models do not explain the style and amount of crater degradation. To the contrary, analyses of degraded crater morphometry indicate modification occurred from creep induced by rain splash combined with surface runoff and erosion; the former process appears to have continued late into Martian history. A critical analysis of the morphology and drainage density of valley networks based on Mars Global Surveyor data shows that these features are, in fact, entirely consistent with rainfall and surface runoff. The necessity for a cold, dry early Mars has been predicated on debatable astronomical and climatic arguments. A warm, wet early climate capable of supporting rainfall and surface runoff is the most plausible scenario for explaining the entire suite of geologic features in the Martian cratered highlands.

@article{doi1010292001je001505,
    author = "Craddock, R. A. and Howard, A. D.",
    title = "The case for rainfall on a warm, wet early Mars",
    year = "2002",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Valley networks provide compelling evidence that past geologic processes on Mars were different than those seen today. The generally accepted paradigm is that these features formed from groundwater circulation, which may have been driven by differential heating induced by magmatic intrusions, impact melt, or a higher primordial heat flux. Although such mechanisms may not require climatic conditions any different than today's, they fail to explain the large amount of recharge necessary for maintaining valley network systems, the spatial patterns of erosion, or how water became initially situated in the Martian regolith. In addition, there are no clear surface manifestations of any geothermal systems (e.g., mineral deposits or phreatic explosion craters). Finally, these models do not explain the style and amount of crater degradation. To the contrary, analyses of degraded crater morphometry indicate modification occurred from creep induced by rain splash combined with surface runoff and erosion; the former process appears to have continued late into Martian history. A critical analysis of the morphology and drainage density of valley networks based on Mars Global Surveyor data shows that these features are, in fact, entirely consistent with rainfall and surface runoff. The necessity for a cold, dry early Mars has been predicated on debatable astronomical and climatic arguments. A warm, wet early climate capable of supporting rainfall and surface runoff is the most plausible scenario for explaining the entire suite of geologic features in the Martian cratered highlands.",
    url = "https://doi.org/10.1029/2001je001505",
    doi = "10.1029/2001je001505",
    openalex = "W2148026027",
    references = "doi1010160009254171900519, doi1010292000je001455, doi10102993je00225, doi101029gm107p0297, doi101029jb091ib13p0e139, doi101038338487a0, doi101038343129a0, doi101038352589a0, openalexw2045435453"
}

Emissivity spectra (1670–200 cm −1) from the Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) show significant differences between bright and dark surfaces, allowing further investigation of their physical and mineralogical character. TES spectra from bright surfaces (albedo ≥0.2) typically show lower emissivity at high wavenumbers (>1300 cm −1) than that of dark surfaces (albedo <0.2). The opposite behavior is evident in the low wavenumbers (<560 cm −1), where bright surfaces have higher emissivity than dark ones. These trends are consistent with the spectral behavior of silicate materials of varying particle size. The short wavelength feature displayed by TES spectra of bright surfaces is a relatively strong absorption that likely is the result of particle size effects of surface silicate particles ≪100 μm in size. A dust cover index (DCI) is developed that exploits this short wavelength feature, serving to identify surfaces that range from dust‐covered to dust‐free. As a gauge of surface‐obscuring silicate dust that can impact spectral measurements, the DCI is more direct than thermal inertia or albedo measurements. Spectral ratio analysis using emissivity spectra from adjacent bright and dark surfaces is explored as a means of deriving the mineralogy of surface dust. The result shows that the dust is dominated by silicate minerals with indication of a significant plagioclase feldspar component.

@article{doi1010292001je001580,
    author = "Ruff, Steven W. and Christensen, P. R.",
    title = "Bright and dark regions on Mars: Particle size and mineralogical characteristics based on Thermal Emission Spectrometer data",
    year = "2002",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Emissivity spectra (1670–200 cm −1) from the Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) show significant differences between bright and dark surfaces, allowing further investigation of their physical and mineralogical character. TES spectra from bright surfaces (albedo ≥0.2) typically show lower emissivity at high wavenumbers (>1300 cm −1) than that of dark surfaces (albedo <0.2). The opposite behavior is evident in the low wavenumbers (<560 cm −1), where bright surfaces have higher emissivity than dark ones. These trends are consistent with the spectral behavior of silicate materials of varying particle size. The short wavelength feature displayed by TES spectra of bright surfaces is a relatively strong absorption that likely is the result of particle size effects of surface silicate particles ≪100 μm in size. A dust cover index (DCI) is developed that exploits this short wavelength feature, serving to identify surfaces that range from dust‐covered to dust‐free. As a gauge of surface‐obscuring silicate dust that can impact spectral measurements, the DCI is more direct than thermal inertia or albedo measurements. Spectral ratio analysis using emissivity spectra from adjacent bright and dark surfaces is explored as a means of deriving the mineralogy of surface dust. The result shows that the dust is dominated by silicate minerals with indication of a significant plagioclase feldspar component.",
    url = "https://doi.org/10.1029/2001je001580",
    doi = "10.1029/2001je001580",
    openalex = "W2136848228",
    references = "doi101029js082i028p04249"
}

@article{doi101038417263a,
    author = "Wyatt, M. B. and McSween, H. Y.",
    title = "Spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of Mars",
    year = "2002",
    journal = "Nature",
    url = "https://doi.org/10.1038/417263a",
    doi = "10.1038/417263a",
    openalex = "W2064546403"
}

Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15% of the layer by weight.

@article{doi101126science1073722,
    author = "Boynton, W. V. and Feldman, W. C. and Squyres, S. W. and Prettyman, T. H. and Brückner, J. and Evans, L. G. and Reedy, R. C. and Starr, R. and Arnold, J. R. and Drake, D. M. and Englert, P. and Metzger, A. E. and Митрофанов, И. Г. and Trombka, J. I. and d’Uston, C. and Wänke, H. and Gasnault, O. and Hamara, D. and Janes, D. M. and Marcialis, R. L. and Maurice, S. and Mikheeva, I. B. and Taylor, G. J. and Tokar, R. and Shinohara, C.",
    title = "Distribution of Hydrogen in the Near Surface of Mars: Evidence for Subsurface Ice Deposits",
    year = "2002",
    journal = "Science",
    abstract = "Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15\% of the layer by weight.",
    url = "https://doi.org/10.1126/science.1073722",
    doi = "10.1126/science.1073722",
    openalex = "W2120397217",
    references = "doi101126science28854752330"
}

@article{doi101016jicarus200309010,
    author = "Smith, M. D.",
    title = "Interannual variability in TES atmospheric observations of Mars during 1999–2003",
    year = "2003",
    journal = "Icarus",
    url = "https://doi.org/10.1016/j.icarus.2003.09.010",
    doi = "10.1016/j.icarus.2003.09.010",
    openalex = "W2074893756",
    references = "doi1010292000je001370"
}

@article{doi101038nature02114,
    author = "Head, J. W. and Mustard, John F. and Kreslavsky, M. A. and Milliken, R. E. and Marchant, D. R.",
    title = "Recent ice ages on Mars",
    year = "2003",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature02114",
    doi = "10.1038/nature02114",
    openalex = "W2070529447",
    references = "doi1010292000je001455, doi101126science28854752330"
}

The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrockare observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.

@article{doi101126science1080885,
    author = "Christensen, P. R. and Bandfield, J. L. and Bell, J. F. and Gorelick, Noel and Hamilton, V. E. and Ivanov, A. B. and Jakosky, B. M. and Kieffer, H. H. and Lane, M. D. and Malin, M. C. and McConnochie, Timothy and McEwen, A. S. and McSween, H. Y. and Mehall, G. and Moersch, Jeffery E. and Nealson, Kenneth H. and Rice, J. W. and Richardson, M. I. and Ruff, Steven W. and Smith, M. D. and Titus, T. N. and Wyatt, M. B.",
    title = "Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results",
    year = "2003",
    journal = "Science",
    abstract = "The Thermal Emission Imaging System (THEMIS) on Mars Odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness, implying temporal changes in the processes or environments during or after their formation. Kilometer-scale exposures of bedrockare observed; elsewhere airfall dust completely mantles the surface over thousands of square kilometers. Mars has compositional variations at 100-meter scales, for example, an exposure of olivine-rich basalt in the walls of Ganges Chasma. Thermally distinct ejecta facies occur around some craters with variations associated with crater age. Polar observations have identified temporal patches of water frost in the north polar cap. No thermal signatures associated with endogenic heat sources have been identified.",
    url = "https://doi.org/10.1126/science.1080885",
    doi = "10.1126/science.1080885",
    openalex = "W2135099653"
}

We have detected a 30,000-square-kilometer area rich in olivine in the Nili Fossae region of Mars. Nili Fossae has been interpreted as a complex of grabens and fractures related to the formation of the Isidis impact basin. We propose that post-impact faulting of this area has exposed subsurface layers rich in olivine. Linear mixture analysis of Thermal Emission Spectrometer spectra shows surface exposures of 30% olivine, where the composition of the olivine ranges from Fo30 to Fo70.

@article{doi101126science1089647,
    author = "Hoefen, Todd M. and Clark, R. N. and Bandfield, J. L. and Smith, M. D. and Pearl, J. C. and Christensen, P. R.",
    title = "Discovery of Olivine in the Nili Fossae Region of Mars",
    year = "2003",
    journal = "Science",
    abstract = "We have detected a 30,000-square-kilometer area rich in olivine in the Nili Fossae region of Mars. Nili Fossae has been interpreted as a complex of grabens and fractures related to the formation of the Isidis impact basin. We propose that post-impact faulting of this area has exposed subsurface layers rich in olivine. Linear mixture analysis of Thermal Emission Spectrometer spectra shows surface exposures of 30\% olivine, where the composition of the olivine ranges from Fo30 to Fo70.",
    url = "https://doi.org/10.1126/science.1089647",
    doi = "10.1126/science.1089647",
    openalex = "W2080404807"
}

Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments.

@article{doi101126science1090544,
    author = "Malin, M. C. and Edgett, K. S.",
    title = "Evidence for Persistent Flow and Aqueous Sedimentation on Early Mars",
    year = "2003",
    journal = "Science",
    abstract = "Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments.",
    url = "https://doi.org/10.1126/science.1090544",
    doi = "10.1126/science.1090544",
    openalex = "W2084431186",
    references = "doi1010160019103574901018, doi1010292000je001364, doi1010292000je001455, doi10102990eo00319, doi10103835084172, doi101093oso97801950993860010001, doi101126science1080885, doi101126science29054981927, openalexw2045435453, openalexw645095896"
}

@incollection{doi10100797803064860053,
    author = "Christensen, P. R. and Jakosky, B. M. and Kieffer, H. H. and Malin, M. C. and McSween, H. Y. and Nealson, Kenneth H. and Mehall, G. and Silverman, Steven H. and Ferry, S. and Caplinger, M. A. and Ravine, M. A.",
    title = "The Thermal Emission Imaging System (Themis) for the Mars 2001 Odyssey Mission",
    year = "2004",
    url = "https://doi.org/10.1007/978-0-306-48600-5\_3",
    doi = "10.1007/978-0-306-48600-5\_3",
    openalex = "W4243063327",
    references = "doi101029js082i028p04249, doi101038202526a0, gillings1996evolution"
}

@article{doi101016jicarus200404005,
    author = "Laskar, J. and Correia, A. C. M. and Gastineau, Mickaël and Joutel, F. and Levrard, B. and Robutel, Philippe",
    title = "Long term evolution and chaotic diffusion of the insolation quantities of Mars",
    year = "2004",
    journal = "Icarus",
    url = "https://doi.org/10.1016/j.icarus.2004.04.005",
    doi = "10.1016/j.icarus.2004.04.005",
    openalex = "W2094459693",
    references = "doi101038352589a0, doi1010510004636120041335, doi101126science2845415790"
}

Neutron data observed using the Neutron Spectrometer aboard 2001 Mars Odyssey provide a lower limit to the global inventory of Martian water‐equivalent hydrogen. Hydrogen‐rich deposits ranging between about 20% and 100% water‐equivalent by mass are found poleward of ±50° latitude, and less rich, but significant, deposits are found at near‐equatorial latitudes. The equatorial deposits between ±45° latitude range between 2% and 10% water‐equivalent hydrogen by mass and reach their maximum in two regions that straddle the 0‐km elevation contour. Higher water abundances, up to ∼11%, are required in subsurface regolith of some equatorial regions if the upper 10 g/cm 2 of regolith is desiccated, as suggested on average by comparison of epithermal and fast neutron data. The hydrogen contents of surface soils in the latitude range between 50° and 80° north and south are equal within data uncertainties. A lower‐limit estimate of the global inventory of near surface hydrogen amounts to a global water layer about 14 cm thick if the reservoir sampled from orbit is assumed to be 1 m thick.

@article{doi1010292003je002160,
    author = "Feldman, W. C. and Prettyman, T. H. and Maurice, S. and Plaut, J. J. and Bish, D. L. and Vaniman, D. T. and Mellon, M. T. and Metzger, A. E. and Squyres, S. W. and Karunatillake, S. and Boynton, W. V. and Elphic, R. C. and Funsten, H. O. and Lawrence, D. J. and Tokar, R. L.",
    title = "Global distribution of near‐surface hydrogen on Mars",
    year = "2004",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Neutron data observed using the Neutron Spectrometer aboard 2001 Mars Odyssey provide a lower limit to the global inventory of Martian water‐equivalent hydrogen. Hydrogen‐rich deposits ranging between about 20\% and 100\% water‐equivalent by mass are found poleward of ±50° latitude, and less rich, but significant, deposits are found at near‐equatorial latitudes. The equatorial deposits between ±45° latitude range between 2\% and 10\% water‐equivalent hydrogen by mass and reach their maximum in two regions that straddle the 0‐km elevation contour. Higher water abundances, up to ∼11\%, are required in subsurface regolith of some equatorial regions if the upper 10 g/cm 2 of regolith is desiccated, as suggested on average by comparison of epithermal and fast neutron data. The hydrogen contents of surface soils in the latitude range between 50° and 80° north and south are equal within data uncertainties. A lower‐limit estimate of the global inventory of near surface hydrogen amounts to a global water layer about 14 cm thick if the reservoir sampled from orbit is assumed to be 1 m thick.",
    url = "https://doi.org/10.1029/2003je002160",
    doi = "10.1029/2003je002160",
    openalex = "W2120973061",
    references = "doi101126science28454191495"
}

@article{doi101038nature02461,
    author = "Bibring, Jean‐Pierre and Langevin, Yves and Poulet, F. and Gendrin, A. and Gondet, B. and Berthé, Michel and Soufflot, A. and Drossart, P. and Combes, M. and Bellucci, G. and Мороз, В. І. and Mangold, N. and Schmitt, B. and the OMEGA team",
    title = "Perennial water ice identified in the south polar cap of Mars",
    year = "2004",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature02461",
    doi = "10.1038/nature02461",
    openalex = "W2008692765"
}

@article{doi101038nature02973,
    author = "Vaniman, D. T. and Bish, D. L. and Chipera, S. J. and Fialips, Claire I. and Carey, J. William and Feldman, W. C.",
    title = "Magnesium sulphate salts and the history of water on Mars",
    year = "2004",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature02973",
    doi = "10.1038/nature02973",
    openalex = "W1981417205"
}

@article{doi101038nature03231,
    author = "Team, The HRSC Co-Investigator and Neukum, G. and Jaumann, R. and Hoffmann, H. and Hauber, Ernst and Head, J. W. and Basilevsky, A. T. and Ivanov, B. A. and Werner, Stéphanie C. and van Gasselt, S. and Murray, John B. and McCord, T. B.",
    title = "Recent and episodic volcanic and glacial activity on Mars revealed by the High Resolution Stereo Camera",
    year = "2004",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature03231",
    doi = "10.1038/nature03231",
    openalex = "W2162469299",
    references = "doi10100797894017103503, doi101023a1011989004263, doi101029jb091ib13p0e139"
}

We report a detection of methane in the martian atmosphere by the Planetary Fourier Spectrometer onboard the Mars Express spacecraft. The global average methane mixing ratio is found to be 10 +/- 5 parts per billion by volume (ppbv). However, the mixing ratio varies between 0 and 30 ppbv over the planet. The source of methane could be either biogenic or nonbiogenic, including past or present subsurface microorganisms, hydrothermal activity, or cometary impacts.

@article{doi101126science1101732,
    author = "Formisano, V. and Atreya, S. K. and Encrenaz, T. and Ignatiev, N. and Giuranna, M.",
    title = "Detection of Methane in the Atmosphere of Mars",
    year = "2004",
    journal = "Science",
    abstract = "We report a detection of methane in the martian atmosphere by the Planetary Fourier Spectrometer onboard the Mars Express spacecraft. The global average methane mixing ratio is found to be 10 +/- 5 parts per billion by volume (ppbv). However, the mixing ratio varies between 0 and 30 ppbv over the planet. The source of methane could be either biogenic or nonbiogenic, including past or present subsurface microorganisms, hydrothermal activity, or cometary impacts.",
    url = "https://doi.org/10.1126/science.1101732",
    doi = "10.1126/science.1101732",
    openalex = "W2139190083"
}

Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.

@article{doi101126science1104559,
    author = "Squyres, S. W. and Grotzinger, J. P. and Arvidson, R. E. and Bell, J. F. and Calvin, W. M. and Christensen, P. R. and Clark, B. C. and Crisp, J. A. and Farrand, W. H. and Herkenhoff, K. E. and Johnson, J. R. and Klingelhöfer, G. and Knoll, Andrew H. and McLennan, S. M. and McSween, H. Y. and Morris, R. V. and Rice, J. W. and Rieder, R. and Soderblom, L. A.",
    title = "In Situ Evidence for an Ancient Aqueous Environment at Meridiani Planum, Mars",
    year = "2004",
    journal = "Science",
    abstract = "Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.",
    url = "https://doi.org/10.1126/science.1104559",
    doi = "10.1126/science.1104559",
    openalex = "W2121006557",
    references = "doi102110scn8209, harms1982structure"
}

@article{doi101016jepsl200509039,
    author = "Grotzinger, J. P. and Arvidson, R. E. and Bell, J. F. and Calvin, W. M. and Clark, B. C. and Fike, David A. and Golombek, M. P. and Greeley, R. and Haldemann, A. F. C. and Herkenhoff, K. E. and Jolliff, B. L. and Knoll, Andrew H. and Malin, M. C. and McLennan, S. M. and Parker, T. J. and Soderblom, L. A. and Sohl‐Dickstein, Jascha and Squyres, S. W. and Tosca, Nicholas J. and Watters, W. A.",
    title = "Stratigraphy and sedimentology of a dry to wet eolian depositional system, Burns formation, Meridiani Planum, Mars",
    year = "2005",
    journal = "Earth and Planetary Science Letters",
    url = "https://doi.org/10.1016/j.epsl.2005.09.039",
    doi = "10.1016/j.epsl.2005.09.039",
    openalex = "W1976011994",
    references = "doi101111j136530911977tb00128x, doi101126science1090544, doi101130gsab28745, doi101306m26490c5, doi102110csp9907, doi102110scn7502, doi102110scn8209, harms1982structure, openalexw2045435453"
}

@article{doi101016jicarus200411023,
    author = "Hartmann, W. K.",
    title = "Martian cratering 8: Isochron refinement and the chronology of Mars",
    year = "2005",
    journal = "Icarus",
    url = "https://doi.org/10.1016/j.icarus.2004.11.023",
    doi = "10.1016/j.icarus.2004.11.023",
    openalex = "W2065782610",
    references = "doi10100797894017103502, doi10100797894017103503, doi10100797894017103504, doi10100797894017103505, doi1010160016703789901506, doi1010160734743x87900698, doi1010292000je001455, doi10102993je00225, doi101029jb091ib13p0e139, doi101126science1090544, doi101126science2214611651, doi105860choice330281"
}

@article{doi101038nature03359,
    author = "Team, The HRSC Co-Investigator and Head, J. W. and Neukum, G. and Jaumann, R. and Hiesinger, H. and Hauber, Ernst and Carr, M. H. and Masson, Ph. and Foing, Bernard and Hoffmann, H. and Kreslavsky, M. A. and Werner, Stéphanie C. and Milkovich, S. M. and van Gasselt, S.",
    title = "Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars",
    year = "2005",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature03359",
    doi = "10.1038/nature03359",
    openalex = "W2168142301",
    references = "doi101023a1011989004263"
}

@article{doi101038nature04274,
    author = "Team, The Omega and Poulet, F. and Bibring, J. P. and Mustard, John F. and Gendrin, A. and Mangold, N. and Langevin, Y. and Arvidson, R. E. and Gondet, B. and Gomez, Cécile",
    title = "Phyllosilicates on Mars and implications for early martian climate",
    year = "2005",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature04274",
    doi = "10.1038/nature04274",
    openalex = "W2100973511",
    references = "doi101126science1108806, doi101126science29054981927"
}

The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) investigation, on board the European Space Agency Mars Express mission, is mapping the surface composition of Mars at a 0.3- to 5-kilometer resolution by means of visible-near-infrared hyperspectral reflectance imagery. The data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy, offering key insights into the evolution of Mars. OMEGA has identified and mapped mafic iron-bearing silicates of both the northern and southern crust, localized concentrations of hydrated phyllosilicates and sulfates but no carbonates, and ices and frosts with a water-ice composition of the north polar perennial cap, as for the south cap, covered by a thin carbon dioxide-ice veneer.

@article{doi101126science1108806,
    author = "Bibring, Jean‐Pierre and Langevin, Yves and Gendrin, A. and Gondet, Brigitte and Poulet, F. and Berthé, Michel and Soufflot, A. and Arvidson, Ray and Mangold, N. and Mustard, J. and Drossart, P. and the OMEGA team",
    title = "Mars Surface Diversity as Revealed by the OMEGA/Mars Express Observations",
    year = "2005",
    journal = "Science",
    abstract = "The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) investigation, on board the European Space Agency Mars Express mission, is mapping the surface composition of Mars at a 0.3- to 5-kilometer resolution by means of visible-near-infrared hyperspectral reflectance imagery. The data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy, offering key insights into the evolution of Mars. OMEGA has identified and mapped mafic iron-bearing silicates of both the northern and southern crust, localized concentrations of hydrated phyllosilicates and sulfates but no carbonates, and ices and frosts with a water-ice composition of the north polar perennial cap, as for the south cap, covered by a thin carbon dioxide-ice veneer.",
    url = "https://doi.org/10.1126/science.1108806",
    doi = "10.1126/science.1108806",
    openalex = "W2098150948",
    references = "doi101016jicarus200404005, doi101038417263a, doi101038nature02461, doi101038nature02973, doi101126science1089647, doi101126science1109087, doi101126science1109091, doi101126science1109098, doi101126science1140516, doi101126science28754581626"
}

The OMEGA/Mars Express hyperspectral imager identified hydrated sulfates on light-toned layered terrains on Mars. Outcrops in Valles Marineris, Margaritifer Sinus, and Terra Meridiani show evidence for kieserite, gypsum, and polyhydrated sulfates. This identification has its basis in vibrational absorptions between 1.3 and 2.5 micrometers. These minerals constitute direct records of the past aqueous activity on Mars.

@article{doi101126science1109087,
    author = "Gendrin, A. and Mangold, N. and Bibring, Jean‐Pierre and Langevin, Y. and Gondet, B. and Poulet, F. and Bonello, G. and Quantin, C. and Mustard, John F. and Arvidson, Ray and Mouëlic, Stéphane Le",
    title = "Sulfates in Martian Layered Terrains: The OMEGA/Mars Express View",
    year = "2005",
    journal = "Science",
    abstract = "The OMEGA/Mars Express hyperspectral imager identified hydrated sulfates on light-toned layered terrains on Mars. Outcrops in Valles Marineris, Margaritifer Sinus, and Terra Meridiani show evidence for kieserite, gypsum, and polyhydrated sulfates. This identification has its basis in vibrational absorptions between 1.3 and 2.5 micrometers. These minerals constitute direct records of the past aqueous activity on Mars.",
    url = "https://doi.org/10.1126/science.1109087",
    doi = "10.1126/science.1109087",
    openalex = "W2103744312",
    references = "doi101126science1108806, doi101126science29054981927"
}

The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) imaging spectrometer observed the northern circumpolar regions of Mars at a resolution of a few kilometers. An extended region at 240 degrees E, 85 degrees N, with an area of 60 kilometers by 200 kilometers, exhibits absorptions at wavelengths of 1.45, 1.75, 1.94, 2.22, 2.26, and 2.48 micrometers. These signatures can be unambiguously attributed to calcium-rich sulfates, most likely gypsum. This region corresponds to the dark longitudinal dunes of Olympia Planitia. These observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains.

@article{doi101126science1109091,
    author = "Langevin, Y. and Poulet, F. and Bibring, Jean‐Pierre and Gondet, B.",
    title = "Sulfates in the North Polar Region of Mars Detected by OMEGA/Mars Express",
    year = "2005",
    journal = "Science",
    abstract = "The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) imaging spectrometer observed the northern circumpolar regions of Mars at a resolution of a few kilometers. An extended region at 240 degrees E, 85 degrees N, with an area of 60 kilometers by 200 kilometers, exhibits absorptions at wavelengths of 1.45, 1.75, 1.94, 2.22, 2.26, and 2.48 micrometers. These signatures can be unambiguously attributed to calcium-rich sulfates, most likely gypsum. This region corresponds to the dark longitudinal dunes of Olympia Planitia. These observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains.",
    url = "https://doi.org/10.1126/science.1109091",
    doi = "10.1126/science.1109091",
    openalex = "W2064799463"
}

Data from the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals olivine, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. Olivine- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in the ancient Noachian-aged units, which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium. Extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials.

@article{doi101126science1109098,
    author = "Mustard, J. F. and Poulet, F. and Gendrin, A. and Bibring, Jean‐Pierre and Langevin, Y. and Gondet, B. and Mangold, N. and Bellucci, G. and Altieri, Francesca",
    title = "Olivine and Pyroxene Diversity in the Crust of Mars",
    year = "2005",
    journal = "Science",
    abstract = "Data from the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) on the Mars Express spacecraft identify the distinct mafic, rock-forming minerals olivine, low-calcium pyroxene (LCP), and high-calcium pyroxene (HCP) on the surface of Mars. Olivine- and HCP-rich regions are found in deposits that span the age range of geologic units. However, LCP-rich regions are found only in the ancient Noachian-aged units, which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium. Extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials.",
    url = "https://doi.org/10.1126/science.1109098",
    doi = "10.1126/science.1109098",
    openalex = "W2111670967"
}

The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick.

@article{doi101126science1122165,
    author = "Picardi, G. and Plaut, J. J. and Biccari, D. and Bombaci, O. and Calabrese, D. and Cartacci, M. and Cicchetti, A. and Clifford, Stephen M. and Edenhofer, P. and Farrell, W. M. and Federico, Costanzo and Frigeri, A. and Gurnett, D. A. and Hagfors, T. and Heggy, Essam and Hèrique, Alain and Huff, Richard and Ivanov, A. B. and Johnson, W.T.K. and Jordan, R. and Kirchner, D. L. and Kofman, W. and Leuschen, C. and Nielsen, Erling and Orosei, R. and Pettinelli, Elena and Phillips, R. J. and Plettemeier, Dirk and Safaeinili, A. and Seu, R. and Stofan, E. R. and Vannaroni, G. and Watters, T. R. and Zampolini, E.",
    title = "Radar Soundings of the Subsurface of Mars",
    year = "2005",
    journal = "Science",
    abstract = "The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick.",
    url = "https://doi.org/10.1126/science.1122165",
    doi = "10.1126/science.1122165",
    openalex = "W2100879731"
}

@article{doi101016jpss200612003,
    author = "Jaumann, R. and Neukum, G. and Behnke, Thomas and Duxbury, T. and Eichentopf, K. and Flohrer, J. and van Gasselt, S. and Giese, B. and Gwinner, K. and Hauber, Ernst and Hoffmann, H. and Hoffmeister, A. and Köhler, Ulrich and Matz, Klaus‐Dieter and McCord, T. B. and Mertens, V. and Oberst, J. and Pischel, R. and Reiss, D. and Ress, E. and Roatsch, T. and Saiger, Peter and Scholten, F. and Schwarz, Gottfried and Stephan, K. and Wählisch, M.",
    title = "The high-resolution stereo camera (HRSC) experiment on Mars Express: Instrument aspects and experiment conduct from interplanetary cruise through the nominal mission",
    year = "2006",
    journal = "Planetary and Space Science",
    url = "https://doi.org/10.1016/j.pss.2006.12.003",
    doi = "10.1016/j.pss.2006.12.003",
    openalex = "W2046910671",
    references = "doi10100797803064860053, doi101017cbo9780511524998, doi1010292000je001364, doi1010292000je001455, doi10102992je00341, doi10103835086515, doi101038nature02114, doi101126science1090544, doi101126science1109087"
}

The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more than 5 km, carrying out the first outcrop‐scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine‐grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg‐sulfates and also include Ca‐sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed near the top of the section. After deposition, interaction with groundwater produced a range of diagenetic features, notably the hematite‐rich concretions known as “blueberries.” The bedrock at Meridiani is highly friable and has undergone substantial erosion by wind‐transported basaltic sand. This sand, along with concretions and concretion fragments eroded from the rock, makes up a soil cover that thinly and discontinuously buries the bedrock. The soil surface exhibits both ancient and active wind ripples that record past and present wind directions. Loose rocks on the soil surface are rare and include both impact ejecta and meteorites. While Opportunity's results show that liquid water was once present at Meridiani Planum below and occasionally at the surface, the environmental conditions recorded were dominantly arid, acidic, and oxidizing and would have posed some significant challenges to the origin of life.

@article{doi1010292006je002771,
    author = "Squyres, S. W. and Arvidson, R. E. and Bollen, David and Bell, J. F. and Brückner, J. and Cabrol, Nathalie A. and Calvin, W. M. and Carr, M. H. and Christensen, P. R. and Clark, B. C. and Crumpler, L. S. and Marais, David J. Des and d’Uston, C. and Economou, T. and Farmer, Jack D. and Farrand, W. H. and Folkner, W. M. and Gellert, R. and Glotch, T. D. and Golombek, M. P. and Gorevan, S. and Grant, J. A. and Greeley, R. and Grotzinger, J. P. and Herkenhoff, K. E. and Hviid, S. F. and Johnson, J. R. and Klingelhöfer, G. and Knoll, Andrew H. and Landis, Geoffrey A. and Lemmon, M. T. and Li, R. and Madsen, M. B. and Malin, M. C. and McLennan, S. M. and McSween, H. Y. and Ming, D. W. and Moersch, J. E. and Morris, R. V. and Parker, T. J. and Rice, J. W. and Richter, L. and Rieder, R. and Schröder, Christian and Sims, M. R. and Smith, M. D. and Smith, Peter H. and Soderblom, L. A. and Sullivan, R. and Tosca, Nicholas J. and Wänke, H. and Wdowiak, T. J. and Wolff, M. J. and Yen, A. S.",
    title = "Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple",
    year = "2006",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more than 5 km, carrying out the first outcrop‐scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine‐grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg‐sulfates and also include Ca‐sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed near the top of the section. After deposition, interaction with groundwater produced a range of diagenetic features, notably the hematite‐rich concretions known as “blueberries.” The bedrock at Meridiani is highly friable and has undergone substantial erosion by wind‐transported basaltic sand. This sand, along with concretions and concretion fragments eroded from the rock, makes up a soil cover that thinly and discontinuously buries the bedrock. The soil surface exhibits both ancient and active wind ripples that record past and present wind directions. Loose rocks on the soil surface are rare and include both impact ejecta and meteorites. While Opportunity's results show that liquid water was once present at Meridiani Planum below and occasionally at the surface, the environmental conditions recorded were dominantly arid, acidic, and oxidizing and would have posed some significant challenges to the origin of life.",
    url = "https://doi.org/10.1029/2006je002771",
    doi = "10.1029/2006je002771",
    openalex = "W1972084009"
}

Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the "phyllocian" era) are found in the oldest terrains; sulfates were formed in a second era (the "theiikian" era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the "siderikian") is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

@article{doi101126science1122659,
    author = "Bibring, Jean‐Pierre and Langevin, Yves and Mustard, John F. and Poulet, F. and Arvidson, R. E. and Gendrin, A. and Gondet, B. and Mangold, N. and Pinet, P. and Forget, F. and Berthé, Michel and Bibring, Jean‐Pierre and Gendrin, A. and Gomez, Cécile and Gondet, B. and Jouglet, D. and Poulet, F. and Soufflot, A. and Vincendon, M. and Combes, M. and Drossart, P. and Encrenaz, Thérèse and Fouchet, Thierry and Merchiorri, Riccardo and Belluci, G. and Altieri, Francesca and Formisano, V. and Capaccioni, F. and Cerroni, P. and Coradini, A. and Fonti, S. and Korablev, Oleg and Kottsov, V. A. and Ignatiev, N. and Мороз, В. І. and Titov, Dimitri and Zasova, Ludmilla and Loiseau, Damien and Mangold, N. and Pinet, P. and Douté, S. and Schmitt, B. and Sotin, C. and Hauber, Ernst and Hoffmann, H. and Jaumann, R. and Keller, U. and Arvidson, Ray and Mustard, John F. and Duxbury, T. C. and Forget, F. and Neukum, G.",
    title = "Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data",
    year = "2006",
    journal = "Science",
    abstract = {Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the "phyllocian" era) are found in the oldest terrains; sulfates were formed in a second era (the "theiikian" era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the "siderikian") is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.},
    url = "https://doi.org/10.1126/science.1122659",
    doi = "10.1126/science.1122659",
    openalex = "W2146376665",
    references = "doi10103835084184, doi101038nature04274, doi101093oso97801950993860010001, doi101126science1058701, doi101126science1104559, doi101126science1108806, doi101126science1109087, doi101126science1109091, doi101126science1109098, openalexw2045435453"
}

The HiRISE camera features a 0.5 m diameter primary mirror, 12 m effective focal length, and a focal plane system that can acquire images containing up to 28 Gb (gigabits) of data in as little as 6 seconds. HiRISE will provide detailed images (0.25 to 1.3 m/pixel) covering ∼1% of the Martian surface during the 2‐year Primary Science Phase (PSP) beginning November 2006. Most images will include color data covering 20% of the potential field of view. A top priority is to acquire ∼1000 stereo pairs and apply precision geometric corrections to enable topographic measurements to better than 25 cm vertical precision. We expect to return more than 12 Tb of HiRISE data during the 2‐year PSP, and use pixel binning, conversion from 14 to 8 bit values, and a lossless compression system to increase coverage. HiRISE images are acquired via 14 CCD detectors, each with 2 output channels, and with multiple choices for pixel binning and number of Time Delay and Integration lines. HiRISE will support Mars exploration by locating and characterizing past, present, and future landing sites, unsuccessful landing sites, and past and potentially future rover traverses. We will investigate cratering, volcanism, tectonism, hydrology, sedimentary processes, stratigraphy, aeolian processes, mass wasting, landscape evolution, seasonal processes, climate change, spectrophotometry, glacial and periglacial processes, polar geology, and regolith properties. An Internet Web site (HiWeb) will enable anyone in the world to suggest HiRISE targets on Mars and to easily locate, view, and download HiRISE data products.

@article{doi1010292005je002605,
    author = "McEwen, A. S. and Eliason, E. M. and Bergstrom, James W. and Bridges, N. T. and Hansen, C. J. and Delamere, W. A. and Grant, J. A. and Gulick, V. C. and Herkenhoff, K. E. and Keszthelyi, L. and Kirk, R. L. and Mellon, M. T. and Squyres, S. W. and Thomas, Nicolas and Weitz, C. M.",
    title = "Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE)",
    year = "2007",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The HiRISE camera features a 0.5 m diameter primary mirror, 12 m effective focal length, and a focal plane system that can acquire images containing up to 28 Gb (gigabits) of data in as little as 6 seconds. HiRISE will provide detailed images (0.25 to 1.3 m/pixel) covering ∼1\% of the Martian surface during the 2‐year Primary Science Phase (PSP) beginning November 2006. Most images will include color data covering 20\% of the potential field of view. A top priority is to acquire ∼1000 stereo pairs and apply precision geometric corrections to enable topographic measurements to better than 25 cm vertical precision. We expect to return more than 12 Tb of HiRISE data during the 2‐year PSP, and use pixel binning, conversion from 14 to 8 bit values, and a lossless compression system to increase coverage. HiRISE images are acquired via 14 CCD detectors, each with 2 output channels, and with multiple choices for pixel binning and number of Time Delay and Integration lines. HiRISE will support Mars exploration by locating and characterizing past, present, and future landing sites, unsuccessful landing sites, and past and potentially future rover traverses. We will investigate cratering, volcanism, tectonism, hydrology, sedimentary processes, stratigraphy, aeolian processes, mass wasting, landscape evolution, seasonal processes, climate change, spectrophotometry, glacial and periglacial processes, polar geology, and regolith properties. An Internet Web site (HiWeb) will enable anyone in the world to suggest HiRISE targets on Mars and to easily locate, view, and download HiRISE data products.",
    url = "https://doi.org/10.1029/2005je002605",
    doi = "10.1029/2005je002605",
    openalex = "W2028483491",
    references = "doi10100797894017103505, doi10100797894017103506, doi1010160016703789901506, doi101017cbo9780511573071, doi1010292000je001370, doi1010292000je001455, doi1010292006je002682, doi1010292006je002808, doi10102994wr00757, doi101038352589a0, doi101126science1090544, doi101126science1104559, doi101126science1108806, doi101126science1109087, doi101126science28854752330, doi101126science29054981927, openalexw2139291338, openalexw2267844404, openalexw2400329996"
}

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is a hyperspectral imager on the Mars Reconnaissance Orbiter (MRO) spacecraft. CRISM consists of three subassemblies, a gimbaled Optical Sensor Unit (OSU), a Data Processing Unit (DPU), and the Gimbal Motor Electronics (GME). CRISM's objectives are (1) to map the entire surface using a subset of bands to characterize crustal mineralogy, (2) to map the mineralogy of key areas at high spectral and spatial resolution, and (3) to measure spatial and seasonal variations in the atmosphere. These objectives are addressed using three major types of observations. In multispectral mapping mode, with the OSU pointed at planet nadir, data are collected at a subset of 72 wavelengths covering key mineralogic absorptions and binned to pixel footprints of 100 or 200 m/pixel. Nearly the entire planet can be mapped in this fashion. In targeted mode the OSU is scanned to remove most along‐track motion, and a region of interest is mapped at full spatial and spectral resolution (15–19 m/pixel, 362–3920 nm at 6.55 nm/channel). Ten additional abbreviated, spatially binned images are taken before and after the main image, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In atmospheric mode, only the EPF is acquired. Global grids of the resulting lower data volume observations are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties. Raw, calibrated, and map‐projected data are delivered to the community with a spectral library to aid in interpretation.

@article{doi1010292006je002682,
    author = "Murchie, S. L. and Arvidson, R. E. and Bedini, P. and Beißer, K. and Bibring, Jean‐Pierre and Bishop, J. L. and Boldt, J. and Cavender, P. J. and Choo, T. and Clancy, R. T. and Darlington, E. H. and Marais, David L. Des and Espiritu, R. C. and Fort, D. and Green, R. and Guinness, E. A. and Hayes, J. R. and Hash, C. and Heffernan, K. J. and Hemmler, J. and Heyler, Gene A. and Humm, D. C. and Hutcheson, Joel C. and Izenberg, N. R. and Lee, R. and Lees, Jeffrey and Lohr, D. and Malaret, E. and Martin, T. Z. and McGovern, J. A. and McGuire, Patrick and Morris, R. V. and Mustard, John F. and Pelkey, S. M. and Rhodes, E. A. and Robinson, M. S. and Roush, T. and Schaefer, Edward D. and Seagrave, Gordon G. and Seelos, F. P. and Silverglate, Peter R. and Slavney, S. and Smith, M. D. and Shyong, Wen-Jong and Strohbehn, K. and Taylor, H. W. and Thompson, Patrick L. and Tossman, B. E. and Wirzburger, M. and Wolff, M. J.",
    title = "Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO)",
    year = "2007",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is a hyperspectral imager on the Mars Reconnaissance Orbiter (MRO) spacecraft. CRISM consists of three subassemblies, a gimbaled Optical Sensor Unit (OSU), a Data Processing Unit (DPU), and the Gimbal Motor Electronics (GME). CRISM's objectives are (1) to map the entire surface using a subset of bands to characterize crustal mineralogy, (2) to map the mineralogy of key areas at high spectral and spatial resolution, and (3) to measure spatial and seasonal variations in the atmosphere. These objectives are addressed using three major types of observations. In multispectral mapping mode, with the OSU pointed at planet nadir, data are collected at a subset of 72 wavelengths covering key mineralogic absorptions and binned to pixel footprints of 100 or 200 m/pixel. Nearly the entire planet can be mapped in this fashion. In targeted mode the OSU is scanned to remove most along‐track motion, and a region of interest is mapped at full spatial and spectral resolution (15–19 m/pixel, 362–3920 nm at 6.55 nm/channel). Ten additional abbreviated, spatially binned images are taken before and after the main image, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In atmospheric mode, only the EPF is acquired. Global grids of the resulting lower data volume observations are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties. Raw, calibrated, and map‐projected data are delivered to the community with a spectral library to aid in interpretation.",
    url = "https://doi.org/10.1029/2006je002682",
    doi = "10.1029/2006je002682",
    openalex = "W2126230369",
    references = "doi101016jicarus200309010, doi101016s0034425798000649, doi1010292000je001455, doi1010292005je002605, doi1010292006je002808, doi101038nature04274, doi101126science1073722, doi101126science1108806, doi101126science1109087, doi101364ao27002502"
}

SHARAD (SHAllow RADar) is a sounding radar provided by Agenzia Spaziale Italiana (ASI) as a Facility Instrument on the Mars Reconnaissance Orbiter mission. Its 20‐MHz center frequency and 10‐MHz bandwidth complement the lower‐frequency, relatively narrower bandwidth capability of the MARSIS sounding radar. A joint Italian‐U.S. team has guided the experiment development and is responsible for data analysis and interpretation. The radar transmits signals at a 700 Hz pulse repetition frequency (PRF) and collects reflections from both the surface and near subsurface of Mars. Vertical and horizontal resolutions are, respectively, 15 m (free‐space) and 3–6 km (cross‐track) by 0.3–1 km (along‐track). The scientific objective of SHARAD is to map, in selected locales, dielectric interfaces to at least several hundred meters depth in the Martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials, including competent rock, soil, water, and ice. A signal‐to‐noise ratio of ∼50 dB (for a specular surface return) is achieved with 10 W of radiated power by using range and azimuth focusing in ground data processing. Preprocessed data as well as range‐ and azimuth‐focused data will be formatted according to Planetary Data System (PDS) standards and be made available from the ASI Science Data Center (ASDC) and from the Geosciences Node of the Planetary Data System (PDS). Important targets for SHARAD include the polar layered deposits, sedimentary stacks (especially in Terra Meridiani), buried channel systems, buried impact craters, volcanic complexes, and shallow ice deposits in equilibrium with the atmosphere.

@article{doi1010292006je002745,
    author = "Seu, R. and Phillips, R. J. and Biccari, D. and Orosei, R. and Masdea, A. and Picardi, G. and Safaeinili, A. and Campbell, B. A. and Plaut, J. J. and Marinangeli, L. and Smrekar, S. E. and Nunes, D. C.",
    title = "SHARAD sounding radar on the Mars Reconnaissance Orbiter",
    year = "2007",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "SHARAD (SHAllow RADar) is a sounding radar provided by Agenzia Spaziale Italiana (ASI) as a Facility Instrument on the Mars Reconnaissance Orbiter mission. Its 20‐MHz center frequency and 10‐MHz bandwidth complement the lower‐frequency, relatively narrower bandwidth capability of the MARSIS sounding radar. A joint Italian‐U.S. team has guided the experiment development and is responsible for data analysis and interpretation. The radar transmits signals at a 700 Hz pulse repetition frequency (PRF) and collects reflections from both the surface and near subsurface of Mars. Vertical and horizontal resolutions are, respectively, 15 m (free‐space) and 3–6 km (cross‐track) by 0.3–1 km (along‐track). The scientific objective of SHARAD is to map, in selected locales, dielectric interfaces to at least several hundred meters depth in the Martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials, including competent rock, soil, water, and ice. A signal‐to‐noise ratio of ∼50 dB (for a specular surface return) is achieved with 10 W of radiated power by using range and azimuth focusing in ground data processing. Preprocessed data as well as range‐ and azimuth‐focused data will be formatted according to Planetary Data System (PDS) standards and be made available from the ASI Science Data Center (ASDC) and from the Geosciences Node of the Planetary Data System (PDS). Important targets for SHARAD include the polar layered deposits, sedimentary stacks (especially in Terra Meridiani), buried channel systems, buried impact craters, volcanic complexes, and shallow ice deposits in equilibrium with the atmosphere.",
    url = "https://doi.org/10.1029/2006je002745",
    doi = "10.1029/2006je002745",
    openalex = "W1969322422"
}

Against a backdrop of intensive exploration of the Martian surface environment, intended to lead to human exploration, some aspects of the modern climate and the meteorology of Mars remain relatively unexplored. In particular, there is a need for detailed measurements of the vertical profiles of atmospheric temperature, water vapor, dust, and condensates to understand the intricately related processes upon which the surface conditions, and those encountered during descent by landers, depend. The most important of these missing data are accurate and extensive temperature measurements with high vertical resolution. The Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter, described here, is the latest attempt to characterize the Martian atmosphere with the sort of coverage and precision achieved by terrestrial weather satellites. If successful, it is expected to lead to corresponding improvements in our understanding of meteorological phenomena and to enable improved general circulation models of the Martian atmosphere for climate studies on a range of timescales.

@article{doi1010292006je002790,
    author = "McCleese, D. J. and Schofield, J. T. and Taylor, F. W. and Calcutt, S. B. and Foote, M. C. and Kass, D. M. and Leovy, Conway Β. and Paige, D. A. and Read, P. L. and Zurek, Richard W.",
    title = "Mars Climate Sounder: An investigation of thermal and water vapor structure, dust and condensate distributions in the atmosphere, and energy balance of the polar regions",
    year = "2007",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Against a backdrop of intensive exploration of the Martian surface environment, intended to lead to human exploration, some aspects of the modern climate and the meteorology of Mars remain relatively unexplored. In particular, there is a need for detailed measurements of the vertical profiles of atmospheric temperature, water vapor, dust, and condensates to understand the intricately related processes upon which the surface conditions, and those encountered during descent by landers, depend. The most important of these missing data are accurate and extensive temperature measurements with high vertical resolution. The Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter, described here, is the latest attempt to characterize the Martian atmosphere with the sort of coverage and precision achieved by terrestrial weather satellites. If successful, it is expected to lead to corresponding improvements in our understanding of meteorological phenomena and to enable improved general circulation models of the Martian atmosphere for climate studies on a range of timescales.",
    url = "https://doi.org/10.1029/2006je002790",
    doi = "10.1029/2006je002790",
    openalex = "W2003158495"
}

The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government‐furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt‐type telescope of catadioptric optical design with a 5.7° field of view, providing a ∼30‐km‐wide swath from ∼290 km altitude; and a 5000‐element CCD with a band pass of 500–700 nm and 7 μ m pixels, giving ∼6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on‐orbit experience. CTX has been allocated 12% of the total MRO data return, or about ≥3 terabits for the nominal mission. This data volume would cover ∼9% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.

@article{doi1010292006je002808,
    author = "Malin, M. C. and Bell, J. F. and Cantor, B. A. and Caplinger, M. A. and Calvin, W. M. and Clancy, R. T. and Edgett, K. S. and Edwards, Lawrence and Haberle, R. M. and James, P. B. and Lee, Steven W. and Ravine, M. A. and Thomas, P. C. and Wolff, M. J.",
    title = "Context Camera Investigation on board the Mars Reconnaissance Orbiter",
    year = "2007",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government‐furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt‐type telescope of catadioptric optical design with a 5.7° field of view, providing a ∼30‐km‐wide swath from ∼290 km altitude; and a 5000‐element CCD with a band pass of 500–700 nm and 7 μ m pixels, giving ∼6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on‐orbit experience. CTX has been allocated 12\% of the total MRO data return, or about ≥3 terabits for the nominal mission. This data volume would cover ∼9\% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.",
    url = "https://doi.org/10.1029/2006je002808",
    doi = "10.1029/2006je002808",
    openalex = "W2076509405",
    references = "doi10100797894017103506, doi1010292000je001370, doi1010292000je001455, doi1010292005je002605, doi1010292006je002682, doi101038nature04274, doi101126science1090544, doi101126science1109087, doi101126science28854752330, doi101126science29054981927"
}

The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 x 10(6) cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick.

@article{doi101126science1139672,
    author = "Plaut, J. J. and Picardi, G. and Safaeinili, A. and Ivanov, A. B. and Milkovich, S. M. and Cicchetti, A. and Kofman, W. and Mouginot, J. and Farrell, W. M. and Phillips, R. J. and Clifford, Stephen M. and Frigeri, A. and Orosei, R. and Federico, Costanzo and Williams, I. P. and Gurnett, D. A. and Nielsen, Erling and Hagfors, T. and Heggy, Essam and Stofan, E. R. and Plettemeier, Dirk and Watters, T. R. and Leuschen, C. and Edenhofer, P.",
    title = "Subsurface Radar Sounding of the South Polar Layered Deposits of Mars",
    year = "2007",
    journal = "Science",
    abstract = "The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 x 10(6) cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick.",
    url = "https://doi.org/10.1126/science.1139672",
    doi = "10.1126/science.1139672",
    openalex = "W2100957654"
}

The objectives of this paper are twofold: first, to report our estimates of the meter‐to‐decameter‐scale topography and slopes of candidate landing sites for the Phoenix mission, based on analysis of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images with a typical pixel scale of 3 m and Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images at 0.3 m pixel −1 and, second, to document in detail the geometric calibration, software, and procedures on which the photogrammetric analysis of HiRISE data is based. A combination of optical design modeling, laboratory observations, star images, and Mars images form the basis for software in the U.S. Geological Survey Integrated Software for Imagers and Spectrometers (ISIS) 3 system that corrects the images for a variety of distortions with single‐pixel or subpixel accuracy. Corrected images are analyzed in the commercial photogrammetric software SOCET SET (® BAE Systems), yielding digital topographic models (DTMs) with a grid spacing of 1 m (3–4 pixels) that require minimal interactive editing. Photoclinometry yields DTMs with single‐pixel grid spacing. Slopes from MOC and HiRISE are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully; only the Mars Exploration Rover (MER) B site in Meridiani Planum is smoother. MOC results at multiple locations have root‐mean‐square (RMS) bidirectional slopes of 0.8–4.5° at baselines of 3–10 m. HiRISE stereopairs (one per final candidate site and one in the former site) yield 1.8–2.8° slopes at 1‐m baseline. Slopes at 1 m from photoclinometry are also in the range 2–3° after correction for image blur. Slopes exceeding the 16° Phoenix safety limit are extremely rare.

@article{doi1010292007je003000,
    author = "Kirk, R. L. and Howington‐Kraus, E. and Rosiek, M. R. and Anderson, James A. and Archinal, B. A. and Becker, K. J. and Cook, D. and Galuszka, D. and Geissler, P. E. and Hare, T. M. and Holmberg, I. M. and Keszthelyi, L. and Redding, B. and Delamere, W. A. and Gallagher, D. L. and Chapel, Jim and Eliason, E. M. and King, Robert A. and McEwen, A. S.",
    title = "Ultrahigh resolution topographic mapping of Mars with MRO HiRISE stereo images: Meter‐scale slopes of candidate Phoenix landing sites",
    year = "2008",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The objectives of this paper are twofold: first, to report our estimates of the meter‐to‐decameter‐scale topography and slopes of candidate landing sites for the Phoenix mission, based on analysis of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images with a typical pixel scale of 3 m and Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) images at 0.3 m pixel −1 and, second, to document in detail the geometric calibration, software, and procedures on which the photogrammetric analysis of HiRISE data is based. A combination of optical design modeling, laboratory observations, star images, and Mars images form the basis for software in the U.S. Geological Survey Integrated Software for Imagers and Spectrometers (ISIS) 3 system that corrects the images for a variety of distortions with single‐pixel or subpixel accuracy. Corrected images are analyzed in the commercial photogrammetric software SOCET SET (® BAE Systems), yielding digital topographic models (DTMs) with a grid spacing of 1 m (3–4 pixels) that require minimal interactive editing. Photoclinometry yields DTMs with single‐pixel grid spacing. Slopes from MOC and HiRISE are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully; only the Mars Exploration Rover (MER) B site in Meridiani Planum is smoother. MOC results at multiple locations have root‐mean‐square (RMS) bidirectional slopes of 0.8–4.5° at baselines of 3–10 m. HiRISE stereopairs (one per final candidate site and one in the former site) yield 1.8–2.8° slopes at 1‐m baseline. Slopes at 1 m from photoclinometry are also in the range 2–3° after correction for image blur. Slopes exceeding the 16° Phoenix safety limit are extremely rare.",
    url = "https://doi.org/10.1029/2007je003000",
    doi = "10.1029/2007je003000",
    openalex = "W2003498164",
    references = "doi1010079783662034774, doi101016104996609290019y, doi1010292000je001364, doi1010292005je002605, doi1010292006je002771, doi1010292006je002790, doi1010510004636120010923, doi101111j147797302005003431x, openalexw2943272530, openalexw2990075684"
}

Light‐toned soils were exposed, through serendipitous excavations by Spirit Rover wheels, at eight locations in the Columbia Hills. Their occurrences were grouped into four types on the basis of geomorphic settings. At three major exposures, the light‐toned soils are hydrous and sulfate‐rich. The spatial distributions of distinct types of salty soils vary substantially: with centimeter‐scaled heterogeneities at Paso Robles, Dead Sea, Shredded, and Champagne‐Penny, a well‐mixed nature for light‐toned soils occurring near and at the summit of Husband Hill, and relatively homogeneous distributions in the two layers at the Tyrone site. Aeolian, fumarolic, and hydrothermal fluid processes are suggested to be responsible for the deposition, transportation, and accumulation of these light‐toned soils. In addition, a change in Pancam spectra of Tyrone yellowish soils was observed after being exposed to current Martian surface conditions for 175 sols. This change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface. Si‐rich nodules and soils were observed near the major exposures of S‐rich soils. They possess a characteristic feature in Pancam visible near‐infrared (Vis‐NIR) spectra that may be diagnostic of hydrated species, and this spectral feature can be used to search for additional Si‐rich species. The exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area. Hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the Neutron Spectrometer on Mars Odyssey.

@article{doi1010292008je003126,
    author = "Wang, Alian and Bell, J. F. and Li, Ron and Johnson, J. R. and Farrand, W. H. and Cloutis, E. A. and Arvidson, R. E. and Crumpler, L. S. and Squyres, S. W. and McLennan, S. M. and Herkenhoff, K. E. and Ruff, Steven W. and Knudson, A. T. and Chen, Wei and Greenberger, R. N.",
    title = "Light‐toned salty soils and coexisting Si‐rich species discovered by the Mars Exploration Rover Spirit in Columbia Hills",
    year = "2008",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Light‐toned soils were exposed, through serendipitous excavations by Spirit Rover wheels, at eight locations in the Columbia Hills. Their occurrences were grouped into four types on the basis of geomorphic settings. At three major exposures, the light‐toned soils are hydrous and sulfate‐rich. The spatial distributions of distinct types of salty soils vary substantially: with centimeter‐scaled heterogeneities at Paso Robles, Dead Sea, Shredded, and Champagne‐Penny, a well‐mixed nature for light‐toned soils occurring near and at the summit of Husband Hill, and relatively homogeneous distributions in the two layers at the Tyrone site. Aeolian, fumarolic, and hydrothermal fluid processes are suggested to be responsible for the deposition, transportation, and accumulation of these light‐toned soils. In addition, a change in Pancam spectra of Tyrone yellowish soils was observed after being exposed to current Martian surface conditions for 175 sols. This change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface. Si‐rich nodules and soils were observed near the major exposures of S‐rich soils. They possess a characteristic feature in Pancam visible near‐infrared (Vis‐NIR) spectra that may be diagnostic of hydrated species, and this spectral feature can be used to search for additional Si‐rich species. The exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area. Hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the Neutron Spectrometer on Mars Odyssey.",
    url = "https://doi.org/10.1029/2008je003126",
    doi = "10.1029/2008je003126",
    openalex = "W2157509927",
    references = "crossref1989evaporite, doi1010160016703784904083, doi101016b9780080166513500287, doi101016jchemgeo200406056, doi101016jjhydrol200612003, doi1010292005je002499, doi1010292007je003000, doi101126science1108806, doi101126science1109087, doi102138rmg2000407, doi106028jres081a011, openalexw1516867372, openalexw1601912106"
}

@article{doi101038nature07097,
    author = "Mustard, John F. and Murchie, S. L. and Pelkey, S. M. and Ehlmann, B. L. and Milliken, R. E. and Grant, J. A. and Bibring, J. P. and Poulet, F. and Bishop, J. L. and Dobrea, E. Noe and Roach, L. H. and Seelos, F. P. and Arvidson, R. E. and Wiseman, S. M. and Green, R. and Hash, C. and Humm, D. C. and Malaret, E. and McGovern, J. A. and Seelos, K. D. and Clancy, T. and Clark, R. N. and Marais, David L. Des and Izenberg, N. R. and Knudson, A. T. and Langevin, Y. and Martin, T. Z. and McGuire, Patrick and Morris, R. V. and Robinson, M. S. and Roush, T. L. and Smith, M. D. and Swayze, Gregg A. and Taylor, H. W. and Titus, T. N. and Wolff, M. J.",
    title = "Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument",
    year = "2008",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature07097",
    doi = "10.1038/nature07097",
    openalex = "W2108201068",
    references = "doi1010292005je002605, doi1010292006je002682, doi1010292006je002808, doi101126science1108806, doi101126science1122659"
}

@article{doi101038ngeo207,
    author = "Ehlmann, B. L. and Mustard, John F. and Fassett, C. I. and Schon, S. C. and Head, J. W. and Marais, David J. Des and Grant, J. A. and Murchie, S. L.",
    title = "Clay minerals in delta deposits and organic preservation potential on Mars",
    year = "2008",
    journal = "Nature Geoscience",
    url = "https://doi.org/10.1038/ngeo207",
    doi = "10.1038/ngeo207",
    openalex = "W2048156731",
    references = "doi1010079783642859168, doi1010291998je000540, doi1010292005je002605"
}

Chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing. Spectrally distinct surface deposits consistent with chloride-bearing materials have been identified and mapped using data from the 2001 Mars Odyssey Thermal Emission Imaging System. These deposits are found throughout regions of low albedo in the southern highlands of Mars. Geomorphologic evidence from orbiting imagery reveals these deposits to be light-toned relative to their surroundings and to be polygonally fractured. The deposits are small (< approximately 25 km(2)) but globally widespread, occurring in middle to late Noachian terrains with a few occurrences in early Hesperian terrains. The identification of chlorides in the ancient southern highlands suggests that near-surface water was available and widespread in early Martian history.

@article{doi101126science1150690,
    author = "Osterloo, M. M. and Hamilton, V. E. and Bandfield, J. L. and Glotch, T. D. and Baldridge, A. M. and Christensen, P. R. and Tornabene, L. L. and Anderson, F. S.",
    title = "Chloride-Bearing Materials in the Southern Highlands of Mars",
    year = "2008",
    journal = "Science",
    abstract = "Chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing. Spectrally distinct surface deposits consistent with chloride-bearing materials have been identified and mapped using data from the 2001 Mars Odyssey Thermal Emission Imaging System. These deposits are found throughout regions of low albedo in the southern highlands of Mars. Geomorphologic evidence from orbiting imagery reveals these deposits to be light-toned relative to their surroundings and to be polygonally fractured. The deposits are small (< approximately 25 km(2)) but globally widespread, occurring in middle to late Noachian terrains with a few occurrences in early Hesperian terrains. The identification of chlorides in the ancient southern highlands suggests that near-surface water was available and widespread in early Martian history.",
    url = "https://doi.org/10.1126/science.1150690",
    doi = "10.1126/science.1150690",
    openalex = "W1978489636",
    references = "doi1010291998je000540, doi1010292005je002605"
}

Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.

@article{doi101126science1164759,
    author = "Ehlmann, B. L. and Mustard, John F. and Murchie, S. L. and Poulet, F. and Bishop, J. L. and Brown, A. J. and Calvin, W. M. and Clark, R. N. and Marais, David J. Des and Milliken, R. E. and Roach, L. H. and Roush, T. L. and Swayze, Gregg A. and Wray, J. J.",
    title = "Orbital Identification of Carbonate-Bearing Rocks on Mars",
    year = "2008",
    journal = "Science",
    abstract = "Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.",
    url = "https://doi.org/10.1126/science.1164759",
    doi = "10.1126/science.1164759",
    openalex = "W1983475289",
    references = "doi1010292006je002682, doi101126science1122659"
}

We design and implement Mars, a MapReduce framework, on graphics processors (GPUs). MapReduce is a distributed programming framework originally proposed by Google for the ease of development of web search applications on a large number of commodity CPUs. Compared with CPUs, GPUs have an order of magnitude higher computation power and memory bandwidth, but are harder to program since their architectures are designed as a special-purpose co-processor and their programming interfaces are typically for graphics applications. As the first attempt to harness GPU's power for MapReduce, we developed Mars on an NVIDIA G80 GPU, which contains over one hundred processors, and evaluated it in comparison with Phoenix, the state-of-the-art MapReduce framework on multi-core CPUs. Mars hides the programming complexity of the GPU behind the simple and familiar MapReduce interface. It is up to 16 times faster than its CPU-based counterpart for six common web applications on a quad-core machine.

@article{doi10114514541151454152,
    author = "He, Bingsheng and Fang, Wenbin and Luo, Qiong and Govindaraju, Naga K. and Wang, Tuyong",
    title = "Mars",
    year = "2008",
    abstract = "We design and implement Mars, a MapReduce framework, on graphics processors (GPUs). MapReduce is a distributed programming framework originally proposed by Google for the ease of development of web search applications on a large number of commodity CPUs. Compared with CPUs, GPUs have an order of magnitude higher computation power and memory bandwidth, but are harder to program since their architectures are designed as a special-purpose co-processor and their programming interfaces are typically for graphics applications. As the first attempt to harness GPU's power for MapReduce, we developed Mars on an NVIDIA G80 GPU, which contains over one hundred processors, and evaluated it in comparison with Phoenix, the state-of-the-art MapReduce framework on multi-core CPUs. Mars hides the programming complexity of the GPU behind the simple and familiar MapReduce interface. It is up to 16 times faster than its CPU-based counterpart for six common web applications on a quad-core machine.",
    url = "https://doi.org/10.1145/1454115.1454152",
    doi = "10.1145/1454115.1454152",
    openalex = "W2129817042",
    references = "doi101109hpca2007346181, doi101109sc200426, doi101111j14678659200701012x, doi10114510157061015800, doi10114511424731142511, doi10114512474801247602, doi10114513274521327492, doi107551mitpress75030030040, openalexw1660390307, openalexw2119547137"
}

@article{doi101016jepsl200906042,
    author = "Carr, M. H. and Head, J. W.",
    title = "Geologic history of Mars",
    year = "2009",
    journal = "Earth and Planetary Science Letters",
    url = "https://doi.org/10.1016/j.epsl.2009.06.042",
    doi = "10.1016/j.epsl.2009.06.042",
    openalex = "W2053544177",
    references = "doi10100797894017103504, doi10100797894017103505, doi10100797894017103506, doi1010160019103588900310, doi101016jicarus200404005, doi101016jicarus200806016, doi1010292000je001370, doi1010292000je001455, doi10102993je00225, doi101029jb091ib13p0e139, doi101038338487a0, doi101038343129a0, doi101038nature04274, doi101126science1073722, doi101126science1090544, doi101126science1109087, doi101126science1122659, doi101126science2845415790, doi102138rmg20066005"
}

@article{doi101016jicarus200909005,
    author = "Levy, J. S. and Marchant, D. R. and Head, J. W.",
    title = "Thermal contraction crack polygons on Mars: A synthesis from HiRISE, Phoenix, and terrestrial analog studies",
    year = "2009",
    journal = "Icarus",
    url = "https://doi.org/10.1016/j.icarus.2009.09.005",
    doi = "10.1016/j.icarus.2009.09.005",
    openalex = "W2100961073",
    references = "doi101002ppp3430010104, doi1010160033589476900375, doi101016jpss200612003, doi102475ajs2578545"
}

The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km 2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near‐infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg‐rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high‐resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low‐grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments.

@article{doi1010292009je003339,
    author = "Ehlmann, B. L. and Mustard, John F. and Swayze, Gregg A. and Clark, R. N. and Bishop, J. L. and Poulet, F. and Marais, David J. Des and Roach, L. H. and Milliken, R. E. and Wray, J. J. and Barnouin, O. S. and Murchie, S. L.",
    title = "Identification of hydrated silicate minerals on Mars using MRO‐CRISM: Geologic context near Nili Fossae and implications for aqueous alteration",
    year = "2009",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km 2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near‐infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg‐rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high‐resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low‐grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments.",
    url = "https://doi.org/10.1029/2009je003339",
    doi = "10.1029/2009je003339",
    openalex = "W2125610349",
    references = "doi10100797894017103506, doi1010292005je002605, doi1010292006je002682, doi1010292006je002808, doi101029jb095ib08p12653, doi101038nature04274, doi101126science1104559, doi101126science1108806, doi101126science1109087, doi101126science1122659, doi10113000167606197687725mobmoa20co2"
}

Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4–3.9 μ m wavelength range, coordinated with higher–spatial resolution HiRISE and Context Imager images. MRO's new high‐resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9–10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate‐bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian‐aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life.

@article{doi1010292009je003342,
    author = "Murchie, S. L. and Mustard, John F. and Ehlmann, B. L. and Milliken, R. E. and Bishop, J. L. and McKeown, N. K. and Dobrea, E. Z. Noe and Seelos, F. P. and Buczkowski, D. L. and Wiseman, S. M. and Arvidson, R. E. and Wray, J. J. and Swayze, Gregg A. and Clark, R. N. and Marais, David J. Des and McEwen, A. S. and Bibring, Jean‐Pierre",
    title = "A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter",
    year = "2009",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4–3.9 μ m wavelength range, coordinated with higher–spatial resolution HiRISE and Context Imager images. MRO's new high‐resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9–10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate‐bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian‐aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life.",
    url = "https://doi.org/10.1029/2009je003342",
    doi = "10.1029/2009je003342",
    openalex = "W2130232949",
    references = "doi1010079783642859168, doi101016jicarus200806016, doi1010291998je000540, doi1010292000je001370, doi1010292005je002605, doi1010292006je002682, doi1010292006je002808, doi1010292009je003339, doi101126science1090544"
}

Living systems produce more than 90% of Earth's atmospheric methane; the balance is of geochemical origin. On Mars, methane could be a signature of either origin. Using high-dispersion infrared spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern early and late summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes, and the maxima of latitudinal profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained approximately 19,000 metric tons of methane, and the estimated source strength (>/=0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California.

@article{doi101126science1165243,
    author = "Mumma, M. J. and Villanueva, Gerónimo and Novak, R. E. and Hewagama, T. and Bonev, B. P. and DiSanti, M. A. and Mandell, Avi M. and Smith, M. D.",
    title = "Strong Release of Methane on Mars in Northern Summer 2003",
    year = "2009",
    journal = "Science",
    abstract = "Living systems produce more than 90\% of Earth's atmospheric methane; the balance is of geochemical origin. On Mars, methane could be a signature of either origin. Using high-dispersion infrared spectrometers at three ground-based telescopes, we measured methane and water vapor simultaneously on Mars over several longitude intervals in northern early and late summer in 2003 and near the vernal equinox in 2006. When present, methane occurred in extended plumes, and the maxima of latitudinal profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained approximately 19,000 metric tons of methane, and the estimated source strength (>/=0.6 kilogram per second) was comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California.",
    url = "https://doi.org/10.1126/science.1165243",
    doi = "10.1126/science.1165243",
    openalex = "W1987622845",
    references = "doi101006icar19941137, doi101016jicarus200407004, doi1010292000je001364, doi101038nature04274, doi101038nature07097, doi10106314823194, doi101126science1101732, doi101126science1102556, doi101126science1122659, doi101126science1127376"
}

New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself.

@article{doi101126science1175307,
    author = "Byrne, Shane and Dundas, C. M. and Kennedy, M. R. and Mellon, M. T. and McEwen, A. S. and Cull, Selby and Daubar, I. J. and Shean, David and Seelos, K. D. and Murchie, S. L. and Cantor, B. A. and Arvidson, R. E. and Edgett, K. S. and Reufer, A. and Thomas, Nicolas and Harrison, T. N. and Posiolova, L. and Seelos, F. P.",
    title = "Distribution of Mid-Latitude Ground Ice on Mars from New Impact Craters",
    year = "2009",
    journal = "Science",
    abstract = "New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself.",
    url = "https://doi.org/10.1126/science.1175307",
    doi = "10.1126/science.1175307",
    openalex = "W2091034152",
    references = "doi1010292006je002808"
}

A kilometers‐thick sedimentary sequence in Gale Crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale. The sequence is divided into two formations, where the Lower formation exhibits a net transition in mineralogy from clay/sulfate to sulfate/oxide assemblages and is separated from the overlying Upper formation by an erosional unconformity. Superposition and crater counts suggest strata in the Lower formation lie along the Noachian‐Hesperian time‐stratigraphic boundary, whereas beds in the Upper formation, which lack signatures indicative of clay minerals or sulfates, are thinner, more regularly spaced, and clearly younger. The observed stratigraphic trends are consistent with the rocks at Gale Crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts.

@article{doi1010292009gl041870,
    author = "Milliken, R. E. and Grotzinger, J. P. and Thomson, Bradley J.",
    title = "Paleoclimate of Mars as captured by the stratigraphic record in Gale Crater",
    year = "2010",
    journal = "Geophysical Research Letters",
    abstract = "A kilometers‐thick sedimentary sequence in Gale Crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale. The sequence is divided into two formations, where the Lower formation exhibits a net transition in mineralogy from clay/sulfate to sulfate/oxide assemblages and is separated from the overlying Upper formation by an erosional unconformity. Superposition and crater counts suggest strata in the Lower formation lie along the Noachian‐Hesperian time‐stratigraphic boundary, whereas beds in the Upper formation, which lack signatures indicative of clay minerals or sulfates, are thinner, more regularly spaced, and clearly younger. The observed stratigraphic trends are consistent with the rocks at Gale Crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts.",
    url = "https://doi.org/10.1029/2009gl041870",
    doi = "10.1029/2009gl041870",
    openalex = "W1596847809",
    references = "doi101126science1090544"
}

Isotopic studies indicate that natural perchlorate is produced on Earth in arid environments by the oxidation of chlorine species through pathways involving ozone or its photochemical products. With this analogy, we propose that the arid environment on Mars may have given rise to perchlorate through the action of atmospheric oxidants. A variety of hypothetical pathways can be proposed including photochemical reactions, electrostatic discharge, and gas‐solid reactions. Because perchlorate‐rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we made a preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorate. We investigated gas phase pathways using a 1‐D photochemical model. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. The feasibility of gas phase production for the Atacama provides justification for future investigations of gas phase photochemistry as a possible source for Martian perchlorate.

@article{doi1010292009je003425,
    author = "Catling, David C. and Claire, Mark W. and Zahnle, Kevin and Quinn, R. C. and Clark, B. C. and Hecht, M. H. and Kounaves, Samuel P.",
    title = "Atmospheric origins of perchlorate on Mars and in the Atacama",
    year = "2010",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Isotopic studies indicate that natural perchlorate is produced on Earth in arid environments by the oxidation of chlorine species through pathways involving ozone or its photochemical products. With this analogy, we propose that the arid environment on Mars may have given rise to perchlorate through the action of atmospheric oxidants. A variety of hypothetical pathways can be proposed including photochemical reactions, electrostatic discharge, and gas‐solid reactions. Because perchlorate‐rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we made a preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorate. We investigated gas phase pathways using a 1‐D photochemical model. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. The feasibility of gas phase production for the Atacama provides justification for future investigations of gas phase photochemistry as a possible source for Martian perchlorate.",
    url = "https://doi.org/10.1029/2009je003425",
    doi = "10.1029/2009je003425",
    openalex = "W2136283672"
}

Serpentine, recently discovered on Mars using Mars Reconnaissance Orbiter data, is uncommon but found in three geologic settings: (1) in mélange terrains at the Claritas Rise and the Nili Fossae, (2) associated with a few southern highlands impact craters, and (3) associated with a regional olivine‐rich stratigraphic unit near the Isidis basin. Any presently active serpentinization processes would be occurring beneath the surface and mineral products would not be apparent with surface and orbital data; however, finding serpentine in several Noachian terrains indicates active serpentinization processes in Mars' past. Important implications are the past production of magnetite, which may contribute to chemical remnant magnetization of Mars' crust, and production of H 2, which is a suitable energy source for chemosynthetic microbial life.

@article{doi1010292010gl042596,
    author = "Ehlmann, B. L. and Mustard, John F. and Murchie, S. L.",
    title = "Geologic setting of serpentine deposits on Mars",
    year = "2010",
    journal = "Geophysical Research Letters",
    abstract = "Serpentine, recently discovered on Mars using Mars Reconnaissance Orbiter data, is uncommon but found in three geologic settings: (1) in mélange terrains at the Claritas Rise and the Nili Fossae, (2) associated with a few southern highlands impact craters, and (3) associated with a regional olivine‐rich stratigraphic unit near the Isidis basin. Any presently active serpentinization processes would be occurring beneath the surface and mineral products would not be apparent with surface and orbital data; however, finding serpentine in several Noachian terrains indicates active serpentinization processes in Mars' past. Important implications are the past production of magnetite, which may contribute to chemical remnant magnetization of Mars' crust, and production of H 2, which is a suitable energy source for chemosynthetic microbial life.",
    url = "https://doi.org/10.1029/2010gl042596",
    doi = "10.1029/2010gl042596",
    openalex = "W1752008511",
    references = "doi1010292009je003339"
}

We use Thermal Emission Imaging System (THEMIS) data to identify and characterize the global distribution of distinct materials interpreted to contain chloride salts on the Martian surface. Previously mapped global geochemical and physical properties are used in concert with thermophysical and morphological observations to assess the materials' local and regional characteristics. The results of our survey have expanded the characterization of the materials from ∼200 to ∼640 distinct sites dispersed throughout low‐albedo Noachian‐ and Hesperian‐aged terrains. Our survey also shows that the materials are detected in locally thermophysically distinct terrains and display a range of morphologies. Topography indicates that the majority of the materials occur in local lows, although crosscutting relationships indicate that some sites are located in “geologic windows” implying that the materials may be older than the terrains in which they are situated. Once exposed, the materials appear to undergo erosion, which may be the reason we do not observe large laterally extensive materials at the surface. The materials are predominantly local in nature, yet their prevalence across the southern highlands suggests that they represent one or more globally ubiquitous processes. We consider a number of formation hypotheses but find that most observations are consistent with formation via ponding of surface runoff or groundwater upwelling, although efflorescence and hydrothermal activity may also be possible in some locales. The materials' inferred ages suggest that the conditions that enabled the deposition of the materials persisted for up to 1 billion years.

@article{doi1010292010je003613,
    author = "Osterloo, M. M. and Anderson, F. S. and Hamilton, V. E. and Hynek, B. M.",
    title = "Geologic context of proposed chloride‐bearing materials on Mars",
    year = "2010",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "We use Thermal Emission Imaging System (THEMIS) data to identify and characterize the global distribution of distinct materials interpreted to contain chloride salts on the Martian surface. Previously mapped global geochemical and physical properties are used in concert with thermophysical and morphological observations to assess the materials' local and regional characteristics. The results of our survey have expanded the characterization of the materials from ∼200 to ∼640 distinct sites dispersed throughout low‐albedo Noachian‐ and Hesperian‐aged terrains. Our survey also shows that the materials are detected in locally thermophysically distinct terrains and display a range of morphologies. Topography indicates that the majority of the materials occur in local lows, although crosscutting relationships indicate that some sites are located in “geologic windows” implying that the materials may be older than the terrains in which they are situated. Once exposed, the materials appear to undergo erosion, which may be the reason we do not observe large laterally extensive materials at the surface. The materials are predominantly local in nature, yet their prevalence across the southern highlands suggests that they represent one or more globally ubiquitous processes. We consider a number of formation hypotheses but find that most observations are consistent with formation via ponding of surface runoff or groundwater upwelling, although efflorescence and hydrothermal activity may also be possible in some locales. The materials' inferred ages suggest that the conditions that enabled the deposition of the materials persisted for up to 1 billion years.",
    url = "https://doi.org/10.1029/2010je003613",
    doi = "10.1029/2010je003613",
    openalex = "W2169071665",
    references = "doi1010292009je003548"
}

@article{doi101038ngeo891,
    author = "Achille, G. Di and Hynek, B. M.",
    title = "Ancient ocean on Mars supported by global distribution of deltas and valleys",
    year = "2010",
    journal = "Nature Geoscience",
    url = "https://doi.org/10.1038/ngeo891",
    doi = "10.1038/ngeo891",
    openalex = "W2023934786",
    references = "doi101016jicarus200806016, doi1010292009je003548"
}

This paper provides a summary of the 2007 Mars Design Reference Architecture 5.0 (DRA 5.0), which is the latest in a series of NASA Mars reference missions. It provides a vision of one potential approach to human Mars exploration, including how Constellation systems could be used. The strategy and example implementation concepts that are described here should not be viewed as constituting a formal plan for the human exploration of Mars, but rather provide a common framework for future planning of systems concepts, technology development, and operational testing as well as potential Mars robotic missions, research that is conducted on the International Space Station, and future potential lunar exploration missions. This summary of the Mars DRA 5.0 provides an overview of the overall mission approach, surface strategy and exploration goals, as well as the key systems and challenges for the first three concepts for human missions to Mars.

@article{doi101109aero20105446736,
    author = "Drake, Bret G. and Hoffman, Stephen J. and Beaty, D. W.",
    title = "Human exploration of Mars, Design Reference Architecture 5.0",
    year = "2010",
    abstract = "This paper provides a summary of the 2007 Mars Design Reference Architecture 5.0 (DRA 5.0), which is the latest in a series of NASA Mars reference missions. It provides a vision of one potential approach to human Mars exploration, including how Constellation systems could be used. The strategy and example implementation concepts that are described here should not be viewed as constituting a formal plan for the human exploration of Mars, but rather provide a common framework for future planning of systems concepts, technology development, and operational testing as well as potential Mars robotic missions, research that is conducted on the International Space Station, and future potential lunar exploration missions. This summary of the Mars DRA 5.0 provides an overview of the overall mission approach, surface strategy and exploration goals, as well as the key systems and challenges for the first three concepts for human missions to Mars.",
    url = "https://doi.org/10.1109/aero.2010.5446736",
    doi = "10.1109/aero.2010.5446736",
    openalex = "W2101215876",
    references = "doi10100797894017103503, doi10100797894017103505, doi101023a1011989004263"
}

@article{doi101016jicarus201105002,
    author = "Thomson, Bradley J. and Bridges, N. T. and Milliken, R. E. and Baldridge, A. M. and Hook, Simon J. and Crowley, James K. and Marion, G. M. and de Souza Filho, Carlos Roberto and Brown, A. J. and Weitz, C. M.",
    title = "Constraints on the origin and evolution of the layered mound in Gale Crater, Mars using Mars Reconnaissance Orbiter data",
    year = "2011",
    journal = "Icarus",
    url = "https://doi.org/10.1016/j.icarus.2011.05.002",
    doi = "10.1016/j.icarus.2011.05.002",
    openalex = "W2093662773",
    references = "doi1010292007je003000"
}

[1] Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light-toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral-bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe-sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg-phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg-phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al-phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg-phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater-filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.

@article{doi1010292010je003694,
    author = "Wray, J. J. and Milliken, R. E. and Dundas, C. M. and Swayze, Gregg A. and Andrews‐Hanna, J. C. and Baldridge, A. M. and Chojnacki, M. and Bishop, J. L. and Ehlmann, B. L. and Murchie, S. L. and Clark, R. N. and Seelos, F. P. and Tornabene, L. L. and Squyres, S. W.",
    title = "Columbus crater and other possible groundwater-fed paleolakes of Terra Sirenum, Mars",
    year = "2011",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "[1] Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light-toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral-bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe-sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg-phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg-phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al-phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg-phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater-filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.",
    url = "https://doi.org/10.1029/2010je003694",
    doi = "10.1029/2010je003694",
    openalex = "W2136811107",
    references = "doi1010292007je003000, doi105962bhltitle45550"
}

@article{doi101038nature10582,
    author = "Ehlmann, B. L. and Mustard, John F. and Murchie, S. L. and Bibring, Jean‐Pierre and Meunier, Alain and Fraeman, A. A. and Langevin, Y.",
    title = "Subsurface water and clay mineral formation during the early history of Mars",
    year = "2011",
    journal = "Nature",
    url = "https://doi.org/10.1038/nature10582",
    doi = "10.1038/nature10582",
    openalex = "W1986859129",
    references = "doi10100797894017103506, doi1010160009254176900012, doi1010160016703789901506, doi1010292009je003339, doi10102993je00225, doi101038nature04274, doi101073pnas95126578, doi101126science1122659, doi101126science2765313734, doi101126science2845415790, openalexw2010625414, openalexw2139291338"
}

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.

@article{doi101089ast20100506,
    author = "Summons, Roger E. and Amend, Jan P. and Bish, D. L. and Buick, Roger and Cody, George D. and Marais, David J. Des and Dromart, Gilles and Eigenbrode, J. L. and Knoll, Andrew H. and Sumner, D. Y.",
    title = "Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group",
    year = "2011",
    journal = "Astrobiology",
    abstract = "The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.",
    url = "https://doi.org/10.1089/ast.2010.0506",
    doi = "10.1089/ast.2010.0506",
    openalex = "W2119246842",
    references = "doi101017s0094837300009994, doi1010291998je000540, doi101126science1165243"
}

The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. The SAM investigation is designed to contribute substantially to the mission goal of quantitatively assessing the habitability of Mars as an essential step in the search for past or present life on Mars. SAM is a 40 kg instrument suite located in the interior of MSL's Curiosity rover. The SAM instruments are a quadrupole mass spectrometer, a tunable laser spectrometer, and a 6-column gas chromatograph all coupled through solid and gas processing systems to provide complementary information on the same samples. The SAM suite is able to measure a suite of light isotopes and to analyze volatiles directly from the atmosphere or thermally released from solid samples. In addition to measurements of simple inorganic compounds and noble gases SAM will conduct a sensitive search for organic compounds with either thermal or chemical extraction from sieved samples delivered by the sample processing system on the Curiosity rover's robotic arm.

@article{doi101007s112140129879z,
    author = "Mahaffy, P. R. and Webster, Christopher R. and Cabane, M. and Conrad, P. G. and Coll, Patrice and Atreya, S. K. and Arvey, Robert and Barciniak, Michael and Benna, M. and Bleacher, L. V. and Brinckerhoff, W. B. and Eigenbrode, J. L. and Carignan, Daniel and Cascia, Mark and Chalmers, Robert A. and Dworkin, Jason P. and Errigo, Therese and Everson, Paula and Franz, H. B. and Farley, Rodger and Feng, Steven and Frazier, Gregory and Freissinet, Caroline and Glavin, D. P. and Harpold, Daniel and Hawk, Douglas and Holmes, Vincent and Johnson, Christopher S. and Jones, Andrea and Jordan, Patrick R. and Kellogg, James and Lewis, Jesse and Lyness, Eric and Malespin, C. A. and Martin, David K. and Maurer, John and McAdam, A. C. and McLennan, Douglas and Nolan, T. and Noriega, Marvin and Pavlov, Alexander A. and Prats, Benito and Raaen, E. and Sheinman, Oren and Sheppard, D. and Smith, James S. and Stern, J. C. and Tan, Florence and Trainer, M. G. and Ming, D. W. and Morris, R. V. and Jones, J. H. and Gundersen, Cindy and Steele, A. and Wray, J. J. and Botta, Oliver and Leshin, L. A. and Owen, Tobias and Battel, Steve and Jakosky, B. M. and Manning, H. L. K. and Squyres, S. W. and Navarro‐González, R. and McKay, Christopher P. and Raulin, F. and Sternberg, R. and Buch, A. and Sorensen, Paul and Kline-Schoder, Robert and Coscia, David and Szopa, Cyril and Teinturier, Samuel and Baffes, Curt and Feldman, Jason and Flesch, Greg and Forouhar, Siamak and Garcia, Ray and Keymeulen, Didier and Woodward, Steve and Block, Bruce and Arnett, Ken and Miller, Ryan and Edmonson, Charles and Gorevan, Stephen and Mumm, E.",
    title = "The Sample Analysis at Mars Investigation and Instrument Suite",
    year = "2012",
    journal = "Space Science Reviews",
    abstract = "The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. The SAM investigation is designed to contribute substantially to the mission goal of quantitatively assessing the habitability of Mars as an essential step in the search for past or present life on Mars. SAM is a 40 kg instrument suite located in the interior of MSL's Curiosity rover. The SAM instruments are a quadrupole mass spectrometer, a tunable laser spectrometer, and a 6-column gas chromatograph all coupled through solid and gas processing systems to provide complementary information on the same samples. The SAM suite is able to measure a suite of light isotopes and to analyze volatiles directly from the atmosphere or thermally released from solid samples. In addition to measurements of simple inorganic compounds and noble gases SAM will conduct a sensitive search for organic compounds with either thermal or chemical extraction from sieved samples delivered by the sample processing system on the Curiosity rover's robotic arm.",
    url = "https://doi.org/10.1007/s11214-012-9879-z",
    doi = "10.1007/s11214-012-9879-z",
    openalex = "W2061420699",
    references = "doi101016jepsl200906042, doi101038338487a0, doi10103835059210, doi101073pnas1106493108, doi101126science1165243, doi101126science2845415790, doi101146annurevastro381427"
}

Scheduled to land in August of 2012, the Mars Science Laboratory (MSL) Mission was initiated to explore the habitability of Mars. This includes both modern environments as well as ancient environments recorded by the stratigraphic rock record preserved at the Gale crater landing site. The Curiosity rover has a designed lifetime of at least one Mars year (∼23 months), and drive capability of at least 20 km. Curiosity’s science payload was specifically assembled to assess habitability and includes a gas chromatograph-mass spectrometer and gas analyzer that will search for organic carbon in rocks, regolith fines, and the atmosphere (SAM instrument); an x-ray diffractometer that will determine mineralogical diversity (CheMin instrument); focusable cameras that can image landscapes and rock/regolith textures in natural color (MAHLI, MARDI, and Mastcam instruments); an alpha-particle x-ray spectrometer for in situ determination of rock and soil chemistry (APXS instrument); a laser-induced breakdown spectrometer to remotely sense the chemical composition of rocks and minerals (ChemCam instrument); an active neutron spectrometer designed to search for water in rocks/regolith (DAN instrument); a weather station to measure modern-day environmental variables (REMS instrument); and a sensor designed for continuous monitoring of background solar and cosmic radiation (RAD instrument). The various payload elements will work together to detect and study potential sampling targets with remote and in situ measurements; to acquire samples of rock, soil, and atmosphere and analyze them in onboard analytical instruments; and to observe the environment around the rover. The 155-km diameter Gale crater was chosen as Curiosity’s field site based on several attributes: an interior mountain of ancient flat-lying strata extending almost 5 km above the elevation of the landing site; the lower few hundred meters of the mountain show a progression with relative age from clay-bearing to sulfate-bearing strata, separated by an unconformity from overlying likely anhydrous strata; the landing ellipse is characterized by a mixture of alluvial fan and high thermal inertia/high albedo stratified deposits; and a number of stratigraphically/geomorphically distinct fluvial features. Samples of the crater wall and rim rock, and more recent to currently active surface materials also may be studied. Gale has a well-defined regional context and strong evidence for a progression through multiple potentially habitable environments. These environments are represented by a stratigraphic record of extraordinary extent, and insure preservation of a rich record of the environmental history of early Mars. The interior mountain of Gale Crater has been informally designated at Mount Sharp, in honor of the pioneering planetary scientist Robert Sharp. The major subsystems of the MSL Project consist of a single rover (with science payload), a Multi-Mission Radioisotope Thermoelectric Generator, an Earth-Mars cruise stage, an entry, descent, and landing system, a launch vehicle, and the mission operations and ground data systems. The primary communication path for downlink is relay through the Mars Reconnaissance Orbiter. The primary path for uplink to the rover is Direct-from-Earth. The secondary paths for downlink are Direct-to-Earth and relay through the Mars Odyssey orbiter. Curiosity is a scaled version of the 6-wheel drive, 4-wheel steering, rocker bogie system from the Mars Exploration Rovers (MER) Spirit and Opportunity and the Mars Pathfinder Sojourner. Like Spirit and Opportunity, Curiosity offers three primary modes of navigation: blind-drive, visual odometry, and visual odometry with hazard avoidance. Creation of terrain maps based on HiRISE (High Resolution Imaging Science Experiment) and other remote sensing data were used to conduct simulated driving with Curiosity in these various modes, and allowed selection of the Gale crater landing site which requires climbing the base of a mountain to achieve its primary science goals. The Sample Acquisition, Processing, and Handling (SA/SPaH) subsystem is responsible for the acquisition of rock and soil samples from the Martian surface and the processing of these samples into fine particles that are then distributed to the analytical science instruments. The SA/SPaH subsystem is also responsible for the placement of the two contact instruments (APXS, MAHLI) on rock and soil targets. SA/SPaH consists of a robotic arm and turret-mounted devices on the end of the arm, which include a drill, brush, soil scoop, sample processing device, and the mechanical and electrical interfaces to the two contact science instruments. SA/SPaH also includes drill bit boxes, the organic check material, and an observation tray, which are all mounted on the front of the rover, and inlet cover mechanisms that are placed over the SAM and CheMin solid sample inlet tubes on the rover top deck.

@article{doi101007s1121401298922,
    author = "Grotzinger, J. P. and Crisp, J. A. and Vasavada, A. R. and Anderson, Robert C. and Baker, Charles J. and Barry, Robert and Blake, D. F. and Conrad, P. G. and Edgett, K. S. and Ferdowski, Bobak and Gellert, R. and Gilbert, John B. and Golombek, M. P. and Gómez‐Elvira, Javier and Hassler, Donald M. and Jandura, Louise and Litvak, M. L. and Mahaffy, P. R. and Maki, J. N. and Meÿer, Michael A. and Malin, M. C. and Митрофанов, И. Г. and Simmonds, John J. and Vaniman, D. T. and Welch, Richard V. and Wiens, R. C.",
    title = "Mars Science Laboratory Mission and Science Investigation",
    year = "2012",
    journal = "Space Science Reviews",
    abstract = "Scheduled to land in August of 2012, the Mars Science Laboratory (MSL) Mission was initiated to explore the habitability of Mars. This includes both modern environments as well as ancient environments recorded by the stratigraphic rock record preserved at the Gale crater landing site. The Curiosity rover has a designed lifetime of at least one Mars year (∼23 months), and drive capability of at least 20 km. Curiosity’s science payload was specifically assembled to assess habitability and includes a gas chromatograph-mass spectrometer and gas analyzer that will search for organic carbon in rocks, regolith fines, and the atmosphere (SAM instrument); an x-ray diffractometer that will determine mineralogical diversity (CheMin instrument); focusable cameras that can image landscapes and rock/regolith textures in natural color (MAHLI, MARDI, and Mastcam instruments); an alpha-particle x-ray spectrometer for in situ determination of rock and soil chemistry (APXS instrument); a laser-induced breakdown spectrometer to remotely sense the chemical composition of rocks and minerals (ChemCam instrument); an active neutron spectrometer designed to search for water in rocks/regolith (DAN instrument); a weather station to measure modern-day environmental variables (REMS instrument); and a sensor designed for continuous monitoring of background solar and cosmic radiation (RAD instrument). The various payload elements will work together to detect and study potential sampling targets with remote and in situ measurements; to acquire samples of rock, soil, and atmosphere and analyze them in onboard analytical instruments; and to observe the environment around the rover. The 155-km diameter Gale crater was chosen as Curiosity’s field site based on several attributes: an interior mountain of ancient flat-lying strata extending almost 5 km above the elevation of the landing site; the lower few hundred meters of the mountain show a progression with relative age from clay-bearing to sulfate-bearing strata, separated by an unconformity from overlying likely anhydrous strata; the landing ellipse is characterized by a mixture of alluvial fan and high thermal inertia/high albedo stratified deposits; and a number of stratigraphically/geomorphically distinct fluvial features. Samples of the crater wall and rim rock, and more recent to currently active surface materials also may be studied. Gale has a well-defined regional context and strong evidence for a progression through multiple potentially habitable environments. These environments are represented by a stratigraphic record of extraordinary extent, and insure preservation of a rich record of the environmental history of early Mars. The interior mountain of Gale Crater has been informally designated at Mount Sharp, in honor of the pioneering planetary scientist Robert Sharp. The major subsystems of the MSL Project consist of a single rover (with science payload), a Multi-Mission Radioisotope Thermoelectric Generator, an Earth-Mars cruise stage, an entry, descent, and landing system, a launch vehicle, and the mission operations and ground data systems. The primary communication path for downlink is relay through the Mars Reconnaissance Orbiter. The primary path for uplink to the rover is Direct-from-Earth. The secondary paths for downlink are Direct-to-Earth and relay through the Mars Odyssey orbiter. Curiosity is a scaled version of the 6-wheel drive, 4-wheel steering, rocker bogie system from the Mars Exploration Rovers (MER) Spirit and Opportunity and the Mars Pathfinder Sojourner. Like Spirit and Opportunity, Curiosity offers three primary modes of navigation: blind-drive, visual odometry, and visual odometry with hazard avoidance. Creation of terrain maps based on HiRISE (High Resolution Imaging Science Experiment) and other remote sensing data were used to conduct simulated driving with Curiosity in these various modes, and allowed selection of the Gale crater landing site which requires climbing the base of a mountain to achieve its primary science goals. The Sample Acquisition, Processing, and Handling (SA/SPaH) subsystem is responsible for the acquisition of rock and soil samples from the Martian surface and the processing of these samples into fine particles that are then distributed to the analytical science instruments. The SA/SPaH subsystem is also responsible for the placement of the two contact instruments (APXS, MAHLI) on rock and soil targets. SA/SPaH consists of a robotic arm and turret-mounted devices on the end of the arm, which include a drill, brush, soil scoop, sample processing device, and the mechanical and electrical interfaces to the two contact science instruments. SA/SPaH also includes drill bit boxes, the organic check material, and an observation tray, which are all mounted on the front of the rover, and inlet cover mechanisms that are placed over the SAM and CheMin solid sample inlet tubes on the rover top deck.",
    url = "https://doi.org/10.1007/s11214-012-9892-2",
    doi = "10.1007/s11214-012-9892-2",
    openalex = "W2087153461",
    references = "doi101126science1090544, doi101126science1165243, doi101126science29054981927"
}

@article{doi101007s1121401299122,
    author = "Maurice, S. and Wiens, R. C. and Saccoccio, M. and Barraclough, B. L. and Gasnault, O. and Forni, O. and Mangold, N. and Baratoux, David and Bender, Steve and Berger, Gilles and Bernardin, John D. and Berthé, Michel and Bridges, N. T. and Blaney, D. L. and Bouyé, M. and Caïs, Phillippe and Clark, B. C. and Clegg, S. M. and Cousin, A. and Cremers, David A. and Cros, A. and DeFlores, Lauren and Derycke, C. and Dingler, B. and Dromart, Gilles and Dubois, Bruno and Dupieux, M. and Durand, Éric and d’Uston, L. and Fabre, C. and Faure, B. and Gaboriaud, Alain and Gharsa, T. and Herkenhoff, K. and Kan, Ed and Kirkland, L. E. and Kouach, Driss and Lacour, J.-L. and Langevin, Y. and Lasue, J. and Mouëlic, Stéphane Le and Lescure, M. and Lewin, É. and Limonadi, D. and Manhès, G. and Mauchien, P. and McKay, Christopher P. and Meslin, Pierre‐Yves and Michel, Yann and Miller, E. and Newsom, H. E. and Orttner, G. and Paillet, A. and Parès, L. and Parot, Yann and Pérez, R. and Pinet, P. and Poitrasson, Franck and Quertier, Benjamin and Sallé, B. and Sotin, C. and Sautter, V. and Séran, H. C. and Simmonds, John J. and Sirven, Jean‐Baptiste and Stiglich, R. and Striebig, Nicolas and Thocaven, J.-J. and Toplis, M. J. and Vaniman, D. T.",
    title = "The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Science Objectives and Mast Unit Description",
    year = "2012",
    journal = "Space Science Reviews",
    url = "https://doi.org/10.1007/s11214-012-9912-2",
    doi = "10.1007/s11214-012-9912-2",
    openalex = "W2037431508",
    references = "doi101016jepsl200906042, openalexw101633874"
}

@article{doi101007s112140129916y,
    author = "Golombek, M. P. and Grant, J. A. and Kipp, D. and Vasavada, A. R. and Kirk, R. and Fergason, R. L. and Bellutta, P. and Calef, F. J. and Larsen, K. and Katayama, Yuji and Huertas, A. and Beyer, R. A. and Chen, A. and Parker, T. J. and Pollard, Brian D. and Lee, S. and Sun, Yuhang and Hoover, R. H. and Sladek, H. and Grotzinger, J. P. and Welch, Richard V. and Dobrea, E. Noe and Michalski, J. R. and Watkins, M. M.",
    title = "Selection of the Mars Science Laboratory Landing Site",
    year = "2012",
    journal = "Space Science Reviews",
    url = "https://doi.org/10.1007/s11214-012-9916-y",
    doi = "10.1007/s11214-012-9916-y",
    openalex = "W2057007402",
    references = "doi1010292007je003000"
}

Impact craters have been used as a standard metric for a plethora of planetary applications for many decades, including age‐dating, geologic mapping and stratigraphic relationships, as tracers for surface processes, and as locations for sampling lower crust and upper mantle material. Utilizing craters for these and other investigations is significantly aided by a uniform catalog of craters across the surface of interest. Consequently, catalogs of craters have been developed for decades for the Moon and other planets. We present a new global catalog of Martian craters statistically complete to diameters D ≥ 1 km. It contains 384,343 craters, and for each crater it lists detailed positional, interior morphologic, ejecta morphologic and morphometric data, and modification state information if it could be determined. In this paper, we detail how the database was created, the different fields assigned, and statistical uncertainties and checks. In our companion paper (Robbins and Hynek, 2012), we discuss the first broad science applications and results of this work.

@article{doi1010292011je003966,
    author = "Robbins, S. J. and Hynek, B. M.",
    title = "A new global database of Mars impact craters ≥1 km: 1. Database creation, properties, and parameters",
    year = "2012",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Impact craters have been used as a standard metric for a plethora of planetary applications for many decades, including age‐dating, geologic mapping and stratigraphic relationships, as tracers for surface processes, and as locations for sampling lower crust and upper mantle material. Utilizing craters for these and other investigations is significantly aided by a uniform catalog of craters across the surface of interest. Consequently, catalogs of craters have been developed for decades for the Moon and other planets. We present a new global catalog of Martian craters statistically complete to diameters D ≥ 1 km. It contains 384,343 craters, and for each crater it lists detailed positional, interior morphologic, ejecta morphologic and morphometric data, and modification state information if it could be determined. In this paper, we detail how the database was created, the different fields assigned, and statistical uncertainties and checks. In our companion paper (Robbins and Hynek, 2012), we discuss the first broad science applications and results of this work.",
    url = "https://doi.org/10.1029/2011je003966",
    doi = "10.1029/2011je003966",
    openalex = "W2063135069",
    references = "doi1010292006je002808"
}

Detection of the organic matter on Mars is one of the main goals of the future Martian landing missions. Yet, the degradation of organic molecules by cosmic ray irradiation on Mars is often ignored. We calculate the radiation dose accumulation rates from solar and galactic cosmic rays at various depths in the shallow Martian subsurface. We demonstrate that a 1‐billion‐year outcrop on Mars accumulates the dosage of ∼500 MGy in the top 0–2 cm and ∼50 MGy at 5–10 cm depths. We show that the preservation of ancient complex organic molecules in the shallow (∼10 cm depth) subsurface of rocks could be highly problematic if the exposure age of a geologic outcrop would exceed 300 Myr. We demonstrate that more simple organic molecules with masses ∼100 amu should have a good chance to survive in the shallow subsurface of rocks. Implications to the sampling strategy for the oncoming Martian missions are discussed.

@article{doi1010292012gl052166,
    author = "Pavlov, A. A. and Pavlov, A. A. and Vasilyev, G. and Ostryakov, V. M. and Pavlov, A. K. and Pavlov, A. K. and Mahaffy, P. R.",
    title = "Degradation of the organic molecules in the shallow subsurface of Mars due to irradiation by cosmic rays",
    year = "2012",
    journal = "Geophysical Research Letters",
    abstract = "Detection of the organic matter on Mars is one of the main goals of the future Martian landing missions. Yet, the degradation of organic molecules by cosmic ray irradiation on Mars is often ignored. We calculate the radiation dose accumulation rates from solar and galactic cosmic rays at various depths in the shallow Martian subsurface. We demonstrate that a 1‐billion‐year outcrop on Mars accumulates the dosage of ∼500 MGy in the top 0–2 cm and ∼50 MGy at 5–10 cm depths. We show that the preservation of ancient complex organic molecules in the shallow (∼10 cm depth) subsurface of rocks could be highly problematic if the exposure age of a geologic outcrop would exceed 300 Myr. We demonstrate that more simple organic molecules with masses ∼100 amu should have a good chance to survive in the shallow subsurface of rocks. Implications to the sampling strategy for the oncoming Martian missions are discussed.",
    url = "https://doi.org/10.1029/2012gl052166",
    doi = "10.1029/2012gl052166",
    openalex = "W1831615840",
    references = "doi101016jepsl200906042"
}

The surface of Mars has preserved the record of early environments in which its basaltic crust was altered by liquid water. These aqueous environments have survived in the form of hydrological morphologies and alteration minerals, including clays and hydrated salts. Because these minerals probe on Earth aqueous environments compatible with biotic activity, understanding their formation processes on Mars is of great exobiological relevance and also offers insight into Earth's now erased ancient water environments. Using remote sensing, we conducted a large‐scale investigation of the distribution, composition, age, and geomorphic settings of hydrous minerals on Mars, providing a sharpened global view of the early aqueous environments and their evolution with time. Aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on Mars (∼4 Gyr). However, very diverse aqueous environments have also been found which suggest widespread, complex aqueous settings from the surface to kilometric depths, and spanning over 1 Gyr. By building a robust statistical sample of detections, the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on Mars and provide context for more localized, in‐depth analyses. Collectively, these trends suggest that at least transient conditions have existed on Mars which may have been favorable for pre‐biotic to biotic activity.

@article{doi1010292012je004145,
    author = "Carter, John and Poulet, F. and Bibring, Jean‐Pierre and Mangold, N. and Murchie, S. L.",
    title = "Hydrous minerals on Mars as seen by the CRISM and OMEGA imaging spectrometers: Updated global view",
    year = "2012",
    journal = "Journal of Geophysical Research Planets",
    abstract = "The surface of Mars has preserved the record of early environments in which its basaltic crust was altered by liquid water. These aqueous environments have survived in the form of hydrological morphologies and alteration minerals, including clays and hydrated salts. Because these minerals probe on Earth aqueous environments compatible with biotic activity, understanding their formation processes on Mars is of great exobiological relevance and also offers insight into Earth's now erased ancient water environments. Using remote sensing, we conducted a large‐scale investigation of the distribution, composition, age, and geomorphic settings of hydrous minerals on Mars, providing a sharpened global view of the early aqueous environments and their evolution with time. Aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on Mars (∼4 Gyr). However, very diverse aqueous environments have also been found which suggest widespread, complex aqueous settings from the surface to kilometric depths, and spanning over 1 Gyr. By building a robust statistical sample of detections, the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on Mars and provide context for more localized, in‐depth analyses. Collectively, these trends suggest that at least transient conditions have existed on Mars which may have been favorable for pre‐biotic to biotic activity.",
    url = "https://doi.org/10.1029/2012je004145",
    doi = "10.1029/2012je004145",
    openalex = "W1484635710",
    references = "doi101016jicarus200806016, doi1010292006je002682, doi1010292009je003339, doi1010292009je003548, doi101038nature10582, openalexw2045435453"
}

Abstract Gale Crater is filled by sedimentary deposits including a mound of layered deposits, Aeolis Mons. Using orbital data, we mapped the crater infillings and measured their geometry to determine their origin. The sediment of Aeolis Mons is interpreted to be primarily air fall material such as dust, volcanic ash, fine‐grained impact products, and possibly snow deposited by settling from the atmosphere, as well as wind‐blown sands cemented in the crater center. Unconformity surfaces between the geological units are evidence for depositional hiatuses. Crater floor material deposited around Aeolis Mons and on the crater wall is interpreted to be alluvial and colluvial deposits. Morphologic evidence suggests that a shallow lake existed after the formation of the lowermost part of Aeolis Mons (the Small yardangs unit and the mass‐wasting deposits). A suite of several features including patterned ground and possible rock glaciers are suggestive of periglacial processes with a permafrost environment after the first hundreds of thousands of years following its formation, dated to ~3.61 Ga, in the Late Noachian/Early Hesperian. Episodic melting of snow in the crater could have caused the formation of sulfates and clays in Aeolis Mons, the formation of rock glaciers and the incision of deep canyons and valleys along its flanks as well as on the crater wall and rim, and the formation of a lake in the deepest portions of Gale.

@article{doi1010022012je004322,
    author = "Deit, L. Le and Hauber, Ernst and Fueten, Frank and Pondrelli, M. and Rossi, Angelo Pio and Jaumann, Ralf",
    title = "Sequence of infilling events in Gale Crater, Mars: Results from morphology, stratigraphy, and mineralogy",
    year = "2013",
    journal = "Journal of Geophysical Research Planets",
    abstract = "Abstract Gale Crater is filled by sedimentary deposits including a mound of layered deposits, Aeolis Mons. Using orbital data, we mapped the crater infillings and measured their geometry to determine their origin. The sediment of Aeolis Mons is interpreted to be primarily air fall material such as dust, volcanic ash, fine‐grained impact products, and possibly snow deposited by settling from the atmosphere, as well as wind‐blown sands cemented in the crater center. Unconformity surfaces between the geological units are evidence for depositional hiatuses. Crater floor material deposited around Aeolis Mons and on the crater wall is interpreted to be alluvial and colluvial deposits. Morphologic evidence suggests that a shallow lake existed after the formation of the lowermost part of Aeolis Mons (the Small yardangs unit and the mass‐wasting deposits). A suite of several features including patterned ground and possible rock glaciers are suggestive of periglacial processes with a permafrost environment after the first hundreds of thousands of years following its formation, dated to \textasciitilde 3.61 Ga, in the Late Noachian/Early Hesperian. Episodic melting of snow in the crater could have caused the formation of sulfates and clays in Aeolis Mons, the formation of rock glaciers and the incision of deep canyons and valleys along its flanks as well as on the crater wall and rim, and the formation of a lake in the deepest portions of Gale.",
    url = "https://doi.org/10.1002/2012je004322",
    doi = "10.1002/2012je004322",
    openalex = "W1728838134",
    references = "doi101016jepsl200912041, doi101016jpss200612003, doi101016jpss201003015, doi102475ajs2578545"
}

@article{doi101016jpss201303006,
    author = "Tanaka, Kenneth L. and Robbins, S. J. and Fortezzo, C. M. and Skinner, J. A. and Hare, T. M.",
    title = "The digital global geologic map of Mars: Chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history",
    year = "2013",
    journal = "Planetary and Space Science",
    url = "https://doi.org/10.1016/j.pss.2013.03.006",
    doi = "10.1016/j.pss.2013.03.006",
    openalex = "W2020615976",
    references = "doi101016jepsl200912041, doi101016jpss201003015"
}

@article{doi101038ngeo2014,
    author = "McEwen, A. S. and Dundas, C. M. and Mattson, S. and Toigo, A. D. and Ojha, L. and Wray, J. J. and Chojnacki, M. and Byrne, Shane and Murchie, S. L. and Thomas, Nicolas",
    title = "Recurring slope lineae in equatorial regions of Mars",
    year = "2013",
    journal = "Nature Geoscience",
    url = "https://doi.org/10.1038/ngeo2014",
    doi = "10.1038/ngeo2014",
    openalex = "W2086277408",
    references = "doi1010292007je003000"
}

We report data on the martian meteorite Northwest Africa (NWA) 7034, which shares some petrologic and geochemical characteristics with known martian meteorites of the SNC (i.e., shergottite, nakhlite, and chassignite) group, but also has some unique characteristics that would exclude it from that group. NWA 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent Rover and Orbiter missions. It formed 2.089 ± 0.081 billion years ago, during the early Amazonian epoch in Mars' geologic history. NWA 7034 has an order of magnitude more indigenous water than most SNC meteorites, with up to 6000 parts per million extraterrestrial H(2)O released during stepped heating. It also has bulk oxygen isotope values of Δ(17)O = 0.58 ± 0.05 per mil and a heat-released water oxygen isotope average value of Δ(17)O = 0.330 ± 0.011 per mil, suggesting the existence of multiple oxygen reservoirs on Mars.

@article{doi101126science1228858,
    author = "Agee, C. B. and Wilson, N. V. and McCubbin, F. M. and Ziegler, K. and Polyak, Victor J. and Sharp, Z. D. and Asmerom, Yemane and Nunn, M. and Shaheen, Robina and Thiemens, M. H. and Steele, A. and Fogel, Marilyn L. and Bowden, R. and Glamoclija, M. and Zhang, Zhisheng and Elardo, S. M.",
    title = "Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034",
    year = "2013",
    journal = "Science",
    abstract = "We report data on the martian meteorite Northwest Africa (NWA) 7034, which shares some petrologic and geochemical characteristics with known martian meteorites of the SNC (i.e., shergottite, nakhlite, and chassignite) group, but also has some unique characteristics that would exclude it from that group. NWA 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent Rover and Orbiter missions. It formed 2.089 ± 0.081 billion years ago, during the early Amazonian epoch in Mars' geologic history. NWA 7034 has an order of magnitude more indigenous water than most SNC meteorites, with up to 6000 parts per million extraterrestrial H(2)O released during stepped heating. It also has bulk oxygen isotope values of Δ(17)O = 0.58 ± 0.05 per mil and a heat-released water oxygen isotope average value of Δ(17)O = 0.330 ± 0.011 per mil, suggesting the existence of multiple oxygen reservoirs on Mars.",
    url = "https://doi.org/10.1126/science.1228858",
    doi = "10.1126/science.1228858",
    openalex = "W2048335161",
    references = "doi101038nature10582"
}

The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

@article{doi101126science1242777,
    author = "Grotzinger, J. P. and Sumner, D. Y. and Kah, Linda C. and Stack, K. M. and Gupta, Sanjeev and Edgar, L. A. and Rubin, David M. and Lewis, K. W. and Schieber, Jüergen and Mangold, N. and Milliken, R. E. and Conrad, P. G. and DesMarais, David J. and Farmer, Jack D. and Siebach, K. L. and Calef, F. J. and Hurowitz, J. A. and McLennan, S. M. and Ming, D. W. and Vaniman, D. T. and Crisp, J. A. and Vasavada, A. R. and Edgett, K. S. and Malin, M. C. and Blake, D. F. and Gellert, R. and Mahaffy, P. R. and Wiens, R. C. and Maurice, S. and Grant, J. A. and Wilson, Sharon A. and Anderson, Robert C. and Beegle, L. W. and Arvidson, R. E. and Hallet, B. and Sletten, R. S. and Rice, M. S. and Bell, J. F. and Griffes, J. L. and Ehlmann, B. L. and Anderson, R. B. and Bristow, T. F. and Dietrich, W. E. and Dromart, Gilles and Eigenbrode, J. L. and Fraeman, A. A. and Hardgrove, C. and Herkenhoff, K. E. and Jandura, Louise and Kocurek, Gary and Lee, S. and Leshin, L. A. and Léveillé, Richard and Limonadi, D. and Maki, J. N. and McCloskey, Scott and Meÿer, Michael A. and Minitti, M. E. and Newsom, H. E. and Oehler, Dorothy Z. and Okon, A. and Palucis, M. C. and Parker, T. J. and Rowland, Scott K. and Schmidt, M. E. and Squyres, S. W. and Steele, A. and Stolper, E. M. and Summons, Roger E. and Treiman, A. H. and Williams, R. M. E. and Yingst, Aileen and Team, MSL Science and Kemppinen, Osku and Bridges, Nathan and Johnson, J. R. and Cremers, David A. and Godber, Austin and Wadhwa, M. and Wellington, Danika and McEwan, Ian and Newman, Claire and Richardson, M. I. and Charpentier, Antoine and Péret, Laurent and King, P. L. and Blank, Jennifer G. and Weigle, Gerald and Li, Shuai and Robertson, Kevin M. and Sun, V. Z. and Baker, Michael and Edwards, Christopher S. and Farley, Kenneth A. and Miller, Hayden and Newcombe, Megan and Pilorget, Cedric and Brunet, Claude and Hipkin, Victoria and Léveillé, Richard",
    title = "A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars",
    year = "2013",
    journal = "Science",
    abstract = "The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.",
    url = "https://doi.org/10.1126/science.1242777",
    doi = "10.1126/science.1242777",
    openalex = "W2054921843",
    references = "doi101086628623, doi101126science1122659, doi101126science29054981927, doi101306212f7e4b2b2411d78648000102c1865d"
}

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.

@article{doi101126science1244734,
    author = "McLennan, S. M. and Anderson, R. B. and Bell, J. F. and Bridges, J. C. and Calef, F. J. and Campbell, John and Clark, B. C. and Clegg, S. M. and Conrad, P. G. and Cousin, A. and Marais, David J. Des and Dromart, Gilles and Dyar, M. D. and Edgar, L. A. and Ehlmann, B. L. and Fabre, C. and Forni, O. and Gasnault, O. and Gellert, R. and Gordon, S. and Grant, J. A. and Grotzinger, J. P. and Gupta, Sanjeev and Herkenhoff, K. E. and Hurowitz, J. A. and King, P. L. and Mouëlic, Stéphane Le and Leshin, L. A. and Léveillé, Richard and Lewis, K. W. and Mangold, N. and Maurice, S. and Ming, D. W. and Morris, R. V. and Nachon, M. and Newsom, H. E. and Ollila, A. and Perrett, G. M. and Rice, M. S. and Schmidt, M. E. and Schwenzer, S. P. and Stack, K. M. and Stolper, Edward M. and Sumner, D. Y. and Treiman, A. H. and VanBommel, S. J. and Vaniman, D. T. and Vasavada, A. R. and Wiens, R. C. and Yingst, R. A. and Team, MSL Science and Kemppinen, Osku and Bridges, Nathan and Johnson, J. R. and Minitti, M. E. and Cremers, David A. and Farmer, Jack D. and Godber, Austin and Wadhwa, M. and Wellington, Danika and McEwan, Ian and Newman, Claire and Richardson, M. I. and Charpentier, Antoine and Péret, Laurent and Blank, Jennifer G. and Weigle, Gerald and Li, Shuai and Milliken, R. E. and Robertson, Kevin M. and Sun, V. Z. and Baker, Michael B. and Edwards, Christopher S. and Farley, Kenneth and Griffes, Jennifer and Miller, Hayden and Newcombe, Megan and Pilorget, Cedric and Siebach, Kirsten and Brunet, C. and Hipkin, Victoria and Marchand, Geneviève and Sánchez, Pablo Sobrón and Favot, Laurent and Cody, George D. and Steele, A. and Flückiger, Lorenzo and Lees, David and Nefian, Ara and Martin, Mildred and Gailhanou, M. and Westall, Francès and Israël, G. and Agard, Christophe and Baroukh, Julien and Donny, Christophe and Gaboriaud, Alain and Guillemot, Philippe and Lafaille, Vivian and Lorigny, Éric",
    title = "Elemental Geochemistry of Sedimentary Rocks at Yellowknife Bay, Gale Crater, Mars",
    year = "2013",
    journal = "Science",
    abstract = "Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.",
    url = "https://doi.org/10.1126/science.1244734",
    doi = "10.1126/science.1244734",
    openalex = "W2112430193",
    references = "doi101017cbo9780511977848, doi101038nature10582"
}

Abstract The investigation of hyperspectral data from the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and the Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié (OMEGA) on Mars Express has revealed an increasingly diverse suite of minerals present on the Martian surface. A revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in CRISM targeted observations and designed to capture the known diversity of surface mineralogy on Mars is presented here as “summary products.” Some of the summary products have strong heritage to OMEGA spectral parameter calculations; this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures. Type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work. Our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface, and successfully highlights and differentiates between locations with differing spectral signatures. The revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations.

@article{doi1010022014je004627,
    author = "Viviano, C. E. and Seelos, F. P. and Murchie, S. L. and Kahn, E. G. and Seelos, K. D. and Taylor, H. W. and Taylor, K. and Ehlmann, B. L. and Wiseman, S. M. and Mustard, John F. and Morgan, M. Frank",
    title = "Revised CRISM spectral parameters and summary products based on the currently detected mineral diversity on Mars",
    year = "2014",
    journal = "Journal of Geophysical Research Planets",
    abstract = "Abstract The investigation of hyperspectral data from the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and the Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié (OMEGA) on Mars Express has revealed an increasingly diverse suite of minerals present on the Martian surface. A revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in CRISM targeted observations and designed to capture the known diversity of surface mineralogy on Mars is presented here as “summary products.” Some of the summary products have strong heritage to OMEGA spectral parameter calculations; this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures. Type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work. Our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface, and successfully highlights and differentiates between locations with differing spectral signatures. The revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations.",
    url = "https://doi.org/10.1002/2014je004627",
    doi = "10.1002/2014je004627",
    openalex = "W1874374897",
    references = "doi1010292009je003339, doi101038nature10582, doi101146annurevearth060313055024"
}

@article{doi101016jicarus201411011,
    author = "Carter, John and Loizeau, D. and Mangold, N. and Poulet, F. and Bibring, Jean‐Pierre",
    title = "Widespread surface weathering on early Mars: A case for a warmer and wetter climate",
    year = "2014",
    journal = "Icarus",
    url = "https://doi.org/10.1016/j.icarus.2014.11.011",
    doi = "10.1016/j.icarus.2014.11.011",
    openalex = "W2021033398",
    references = "doi101016jepsl200912041, doi1010292009je003548"
}

A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth-including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.

@article{doi101089ast20141227,
    author = "Rummel, John D. and Beaty, D. W. and Jones, Melissa A. and Bakermans, Corien and Barlow, N. G. and Boston, Penelope J. and Chevrier, V. F. and Clark, B. C. and de Vera, Jean‐Pierre and Gough, R. V. and Hallsworth, John E. and Head, J. W. and Hipkin, V. and Kieft, Thomas L. and McEwen, A. S. and Mellon, M. T. and Mikucki, Jill A. and Nicholson, Wayne L. and Omelon, Christopher R. and Peterson, R. C. and Roden, Eric and Lollar, Barbara Sherwood and Tanaka, Kenneth L. and Viola, D. and Wray, J. J.",
    title = "A New Analysis of Mars “Special Regions”: Findings of the Second MEPAG Special Regions Science Analysis Group (SR-SAG2)",
    year = "2014",
    journal = "Astrobiology",
    abstract = {A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth-including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.},
    url = "https://doi.org/10.1089/ast.2014.1227",
    doi = "10.1089/ast.2014.1227",
    openalex = "W1993772166",
    references = "doi101016jepsl200906042, doi1010292004je002240, doi1010292007jg000677, doi1010292009je003339, doi101126science1165243, doi101130g223521, doi101130spe70p1, doi101146annurevearth060313055024"
}

Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source.

@article{doi101126science1261713,
    author = "Webster, Christopher R. and Mahaffy, P. R. and Atreya, S. K. and Flesch, Gregory J. and Mischna, M. A. and Meslin, Pierre‐Yves and Farley, Kenneth A. and Conrad, P. G. and Christensen, L. E. and Pavlov, Alexander A. and Martín‐Torres, Javier and Zorzano, María‐Paz and McConnochie, T. H. and Owen, Tobias and Eigenbrode, J. L. and Glavin, D. P. and Steele, A. and Malespin, C. A. and Archer, P. D. and Sutter, B. and Coll, Patrice and Freissinet, Caroline and McKay, Christopher P. and Moores, John E. and Schwenzer, S. P. and Bridges, J. C. and Navarro‐González, R. and Gellert, R. and Lemmon, M. T. and the MSL Science Team",
    title = "Mars methane detection and variability at Gale crater",
    year = "2014",
    journal = "Science",
    abstract = "Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95\% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95\% CI), implying that Mars is episodically producing methane from an additional unknown source.",
    url = "https://doi.org/10.1126/science.1261713",
    doi = "10.1126/science.1261713",
    openalex = "W1977251152",
    references = "doi101126science1165243"
}

Abstract We present results from geomorphic mapping and visible to near‐infrared spectral analyses of the Jezero crater paleolake basin and its associated watershed. The goal of this study is to understand the provenance of the sedimentary deposits within this open‐basin lake using a source‐to‐sink approach. Two fan deposits located within the basin have distinct visible to near‐infrared mineralogic signatures measured by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The northern fan is spectrally characterized by a mixture of Mg‐rich carbonate and olivine, while the western fan is characterized by Fe/Mg‐smectite (e.g., saponite or nontronite) with variable amounts of Mg‐rich carbonate and olivine in isolated exposures. The watersheds of these deposits contain a variety of geomorphic units that are likely to have supplied sediment to the Jezero crater paleolake, as the fluvial valleys that fed the basin incise these units. The geomorphic units include exposures of Fe/Mg‐smectite‐, olivine‐, and Mg‐rich carbonate‐bearing terrain. We show that the difference in fan deposit mineralogy is a function of the areal exposure of the major geomorphic units within their watersheds. This indicates that the spectrally dominant aqueous alteration minerals in the fan deposits are primarily detrital, or transported, in nature and did not form in situ. We conclude that the aqueous alteration of the units in the watershed occurred prior to the fluvial activity that carved the valleys of the Jezero crater paleolake system, and that the two periods of aqueous activity are not genetically related.

@article{doi1010022014je004782,
    author = "Goudge, T. A. and Mustard, John F. and Head, J. W. and Fassett, C. I. and Wiseman, S. M.",
    title = "Assessing the mineralogy of the watershed and fan deposits of the Jezero crater paleolake system, Mars",
    year = "2015",
    journal = "Journal of Geophysical Research Planets",
    abstract = "Abstract We present results from geomorphic mapping and visible to near‐infrared spectral analyses of the Jezero crater paleolake basin and its associated watershed. The goal of this study is to understand the provenance of the sedimentary deposits within this open‐basin lake using a source‐to‐sink approach. Two fan deposits located within the basin have distinct visible to near‐infrared mineralogic signatures measured by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The northern fan is spectrally characterized by a mixture of Mg‐rich carbonate and olivine, while the western fan is characterized by Fe/Mg‐smectite (e.g., saponite or nontronite) with variable amounts of Mg‐rich carbonate and olivine in isolated exposures. The watersheds of these deposits contain a variety of geomorphic units that are likely to have supplied sediment to the Jezero crater paleolake, as the fluvial valleys that fed the basin incise these units. The geomorphic units include exposures of Fe/Mg‐smectite‐, olivine‐, and Mg‐rich carbonate‐bearing terrain. We show that the difference in fan deposit mineralogy is a function of the areal exposure of the major geomorphic units within their watersheds. This indicates that the spectrally dominant aqueous alteration minerals in the fan deposits are primarily detrital, or transported, in nature and did not form in situ. We conclude that the aqueous alteration of the units in the watershed occurred prior to the fluvial activity that carved the valleys of the Jezero crater paleolake system, and that the two periods of aqueous activity are not genetically related.",
    url = "https://doi.org/10.1002/2014je004782",
    doi = "10.1002/2014je004782",
    openalex = "W1920771549",
    references = "doi10100797814757115239, doi101016jicarus200806016, doi1010292006je002808, doi1010292009je003339, doi1010292009je003548, doi101130001676061951621tceoda20co2"
}

Abstract We use a 3‐D general circulation model to compare the primitive Martian hydrological cycle in “warm and wet” and “cold and icy” scenarios. In the warm and wet scenario, an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice‐free northern ocean. Precipitation shows strong surface variations, with high rates around Hellas basin and west of Tharsis but low rates around Margaritifer Sinus (where the observed valley network drainage density is nonetheless high). In the cold and icy scenario, snow migration is a function of both obliquity and surface pressure, and limited episodic melting is possible through combinations of seasonal, volcanic, and impact forcing. At surface pressures above those required to avoid atmospheric collapse (∼0.5 bar) and moderate to high obliquity, snow is transported to the equatorial highland regions where the concentration of valley networks is highest. Snow accumulation in the Aeolis quadrangle is high, indicating an ice‐free northern ocean is not required to supply water to Gale crater. At lower surface pressures and obliquities, both H 2 O and CO 2 are trapped as ice at the poles and the equatorial regions become extremely dry. The valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41.8 ∘ obliquity but uncorrelated with precipitation produced by the warm and wet simulation. Because our simulations make specific predictions for precipitation patterns under different climate scenarios, they motivate future targeted geological studies.

@article{doi1010022015je004787,
    author = "Wordsworth, Robin and Kerber, L. and Pierrehumbert, Raymond T. and Forget, F. and Head, J. W.",
    title = "Comparison of “warm and wet” and “cold and icy” scenarios for early Mars in a 3‐D climate model",
    year = "2015",
    journal = "Journal of Geophysical Research Planets",
    abstract = "Abstract We use a 3‐D general circulation model to compare the primitive Martian hydrological cycle in “warm and wet” and “cold and icy” scenarios. In the warm and wet scenario, an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice‐free northern ocean. Precipitation shows strong surface variations, with high rates around Hellas basin and west of Tharsis but low rates around Margaritifer Sinus (where the observed valley network drainage density is nonetheless high). In the cold and icy scenario, snow migration is a function of both obliquity and surface pressure, and limited episodic melting is possible through combinations of seasonal, volcanic, and impact forcing. At surface pressures above those required to avoid atmospheric collapse (∼0.5 bar) and moderate to high obliquity, snow is transported to the equatorial highland regions where the concentration of valley networks is highest. Snow accumulation in the Aeolis quadrangle is high, indicating an ice‐free northern ocean is not required to supply water to Gale crater. At lower surface pressures and obliquities, both H 2 O and CO 2 are trapped as ice at the poles and the equatorial regions become extremely dry. The valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41.8 ∘ obliquity but uncorrelated with precipitation produced by the warm and wet simulation. Because our simulations make specific predictions for precipitation patterns under different climate scenarios, they motivate future targeted geological studies.",
    url = "https://doi.org/10.1002/2015je004787",
    doi = "10.1002/2015je004787",
    openalex = "W1875794043",
    references = "doi1010292009je003548"
}

@article{doi101007s112140150139x,
    author = "Jakosky, B. M. and Lin, R. P. and Grebowsky, J. M. and Luhmann, J. G. and Mitchell, David F. and Beutelschies, G. and Priser, T. and Acuña, M. H. and Andersson, L. and Baird, Darren and Baker, D. N. and Bartlett, R. O. and Benna, M. and Bougher, S. W. and Brain, D. A. and Carson, D. and Cauffman, Sandra and Chamberlin, Phillip C. and Chaufray, Jean‐Yves and Cheatom, Oscar and Clarke, J. T. and Connerney, J. E. P. and Cravens, T. E. and Curtis, D. and Delory, G. T. and Demcak, Stuart and DeWolfe, A. W. and Eparvier, F. G. and Ergun, R. E. and Eriksson, A. I. and Espley, J. R. and Fang, Xiaohua and Folta, David and Fox, Jane L. and Gomez-Rosa, Carlos and Habenicht, S. and Halekas, J. S. and Holsclaw, G. M. and Houghton, M. B. and Howard, R. A. and Jarosz, M. and Jedrich, Nicholas M. and Johnson, Micah and Kasprzak, W. T. and Kelley, M. S. and King, T. and Lankton, M. R. and Larson, D. E. and Leblanc, François and Lefèvre, Franck and Lillis, R. J. and Mahaffy, P. R. and Mazelle, C. and McClintock, W. E. and McFadden, J. and Mitchell, D. L. and Montmessin, Franck and Morrissey, James R. and Peterson, W. K. and Possel, W. and Sauvaud, J. A. and Schneider, N. M. and Sidney, Wayne and Sparacino, S. and Stewart, A. I. F. and Tolson, R. and Toublanc, D. and Waters, Conor and Woods, T. N. and Yelle, R. V. and Zurek, Richard W.",
    title = "The Mars Atmosphere and Volatile Evolution (MAVEN) Mission",
    year = "2015",
    journal = "Space Science Reviews",
    url = "https://doi.org/10.1007/s11214-015-0139-x",
    doi = "10.1007/s11214-015-0139-x",
    openalex = "W2053823809",
    references = "doi101016jicarus200806016, doi101126science1090544, doi101126science1122659, doi101126science2845415790, openalexw2045435453"
}

@article{doi101038ngeo2546,
    author = "Ojha, L. and Wilhelm, Mary Beth and Murchie, S. L. and McEwen, A. S. and Wray, J. J. and Hanley, J. and Massé, M. and Chojnacki, M.",
    title = "Spectral evidence for hydrated salts in recurring slope lineae on Mars",
    year = "2015",
    journal = "Nature Geoscience",
    url = "https://doi.org/10.1038/ngeo2546",
    doi = "10.1038/ngeo2546",
    openalex = "W2152001765",
    references = "doi1010292005je002605, doi1010292006je002682, doi101146annurevearth060313055024"
}

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

@article{doi101126scienceaac7575,
    author = "Grotzinger, J. P. and Gupta, Sanjeev and Malin, M. C. and Rubin, David M. and Schieber, Jüergen and Siebach, K. L. and Sumner, D. Y. and Stack, K. M. and Vasavada, A. R. and Arvidson, R. E. and Calef, F. J. and Edgar, Lauren and Fischer, W. and Grant, J. A. and Griffes, J. L. and Kah, Linda C. and Lamb, Michael P. and Lewis, K. W. and Mangold, N. and Minitti, M. E. and Palucis, M. C. and Rice, M. S. and Williams, R. M. E. and Yingst, R. A. and Blake, D. F. and Blaney, D. L. and Conrad, P. G. and Crisp, J. A. and Dietrich, W. E. and Dromart, Gilles and Edgett, K. S. and Ewing, R. C. and Gellert, R. and Hurowitz, J. A. and Kocurek, Gary and Mahaffy, Paul and McBride, M. J. and McLennan, S. M. and Mischna, M. and Ming, D. W. and Milliken, R. E. and Newsom, H. E. and Oehler, Dorothy Z. and Parker, T. J. and Vaniman, D. T. and Wiens, R. C. and Wilson, Sharon A.",
    title = "Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars",
    year = "2015",
    journal = "Science",
    abstract = "The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).",
    url = "https://doi.org/10.1126/science.aac7575",
    doi = "10.1126/science.aac7575",
    openalex = "W1895144666",
    references = "doi101038ngeo730, doi10108000221680309499956, doi101111j136530911977tb00128x, doi101126science1090544, doi1013065ceadd7616bb11d78645000102c1865d"
}

The nature of the early martian climate is one of the major unanswered questions of planetary science. Key challenges remain, but a new wave of orbital and in situ observations and improvements in climate modeling have led to significant advances over the past decade. Multiple lines of geologic evidence now point to an episodically warm surface during the late Noachian and early Hesperian periods 3–4 Ga. The low solar flux received by Mars in its first billion years and inefficiency of plausible greenhouse gases such as CO 2 mean that the steady-state early martian climate was likely cold. A denser CO 2 atmosphere would have caused adiabatic cooling of the surface and hence migration of water ice to the higher-altitude equatorial and southern regions of the planet. Transient warming caused melting of snow and ice deposits and a temporarily active hydrological cycle, leading to erosion of the valley networks and other fluvial features. Precise details of the warming mechanisms remain unclear, but impacts, volcanism, and orbital forcing all likely played an important role. The lack of evidence for glaciation across much of Mars's ancient terrain suggests the late Noachian surface water inventory was not sufficient to sustain a northern ocean. Though mainly inhospitable on the surface, early Mars may nonetheless have presented significant opportunities for the development of microbial life.

@article{doi101146annurevearth060115012355,
    author = "Wordsworth, Robin D.",
    title = "The Climate of Early Mars",
    year = "2016",
    journal = "Annual Review of Earth and Planetary Sciences",
    abstract = "The nature of the early martian climate is one of the major unanswered questions of planetary science. Key challenges remain, but a new wave of orbital and in situ observations and improvements in climate modeling have led to significant advances over the past decade. Multiple lines of geologic evidence now point to an episodically warm surface during the late Noachian and early Hesperian periods 3–4 Ga. The low solar flux received by Mars in its first billion years and inefficiency of plausible greenhouse gases such as CO 2 mean that the steady-state early martian climate was likely cold. A denser CO 2 atmosphere would have caused adiabatic cooling of the surface and hence migration of water ice to the higher-altitude equatorial and southern regions of the planet. Transient warming caused melting of snow and ice deposits and a temporarily active hydrological cycle, leading to erosion of the valley networks and other fluvial features. Precise details of the warming mechanisms remain unclear, but impacts, volcanism, and orbital forcing all likely played an important role. The lack of evidence for glaciation across much of Mars's ancient terrain suggests the late Noachian surface water inventory was not sufficient to sustain a northern ocean. Though mainly inhospitable on the surface, early Mars may nonetheless have presented significant opportunities for the development of microbial life.",
    url = "https://doi.org/10.1146/annurev-earth-060115-012355",
    doi = "10.1146/annurev-earth-060115-012355",
    openalex = "W2416138856",
    references = "doi101016jepsl200906042, doi101016jepsl201110040, doi1010292009je003339, doi1010292009je003548, doi101038nature10582, doi101146annurevearth060313055024"
}

Abstract The evidence for abundant liquid water on early Mars despite the faint young Sun is a long‐standing problem in planetary research. Here we present new ab initio spectroscopic and line‐by‐line climate calculations of the warming potential of reduced atmospheres on early Mars. We show that the strength of both CO 2 –H 2 and CO 2 –CH 4 collision‐induced absorption (CIA) has previously been significantly underestimated. Contrary to previous expectations, methane could have acted as a powerful greenhouse gas on early Mars due to CO 2 –CH 4 CIA in the critical 250–500 cm −1 spectral window region. In atmospheres of 0.5 bar CO 2 or more, percent levels of H 2 or CH 4 raise annual mean surface temperatures by tens of degrees, with temperatures reaching 273 K for pressures of 1.25–2 bars and 2–10% of H 2 and CH 4. Methane and hydrogen produced following aqueous alteration of Mars' crust could have combined with volcanically outgassed CO 2 to form transient atmospheres of this composition 4.5–3.5 Ga. Our results also suggest that inhabited exoplanets could retain surface liquid water at significant distances from their host stars.

@article{doi1010022016gl071766,
    author = "Wordsworth, Robin and Kalugina, Yulia N. and Lokshtanov, S.E. and Vigasin, A. A. and Ehlmann, B. L. and Head, J. W. and Sanders, Cecilia and Wang, Huize",
    title = "Transient reducing greenhouse warming on early Mars",
    year = "2017",
    journal = "Geophysical Research Letters",
    abstract = "Abstract The evidence for abundant liquid water on early Mars despite the faint young Sun is a long‐standing problem in planetary research. Here we present new ab initio spectroscopic and line‐by‐line climate calculations of the warming potential of reduced atmospheres on early Mars. We show that the strength of both CO 2 –H 2 and CO 2 –CH 4 collision‐induced absorption (CIA) has previously been significantly underestimated. Contrary to previous expectations, methane could have acted as a powerful greenhouse gas on early Mars due to CO 2 –CH 4 CIA in the critical 250–500 cm −1 spectral window region. In atmospheres of 0.5 bar CO 2 or more, percent levels of H 2 or CH 4 raise annual mean surface temperatures by tens of degrees, with temperatures reaching 273 K for pressures of 1.25–2 bars and 2–10\% of H 2 and CH 4. Methane and hydrogen produced following aqueous alteration of Mars' crust could have combined with volcanically outgassed CO 2 to form transient atmospheres of this composition 4.5–3.5 Ga. Our results also suggest that inhabited exoplanets could retain surface liquid water at significant distances from their host stars.",
    url = "https://doi.org/10.1002/2016gl071766",
    doi = "10.1002/2016gl071766",
    openalex = "W2545903499",
    references = "doi1010292009je003548"
}

The Colour and Stereo Surface Imaging System (CaSSIS) is the main imaging system onboard the European Space Agency’s ExoMars Trace Gas Orbiter (TGO) which was launched on 14 March 2016. CaSSIS is intended to acquire moderately high resolution (4.6 m/pixel) targeted images of Mars at a rate of 10–20 images per day from a roughly circular orbit 400 km above the surface. Each image can be acquired in up to four colours and stereo capability is foreseen by the use of a novel rotation mechanism. A typical product from one image acquisition will be a $9.5~\mbox{km} \times {\sim}45~\mbox{km}$ swath in full colour and stereo in one over-flight of the target thereby reducing atmospheric influences inherent in stereo and colour products from previous high resolution imagers. This paper describes the instrument including several novel technical solutions required to achieve the scientific requirements.

@article{doi101007s1121401704211,
    author = "Thomas, N. and Cremonese, G. and Ziethe, R. and Gerber, M. and Brändli, Mathias and Bruno, G. and Erismann, M. and Gambicorti, L. and Gerber, T. and Ghose, K. and Gruber, Mario and Gubler, P. and Mischler, H. and Jost, J. and Piazza, D. and Pommerol, A. and Rieder, Markus and Roloff, V. and Servonet, A. and Trottmann, W. and Uthaicharoenpong, T. and Zimmermann, C. and Vernani, Dervis and Johnson, Micah and Pelò, E. and Weigel, Thomas and Viertl, Jacques and Roux, Nicolas and Lochmatter, P. and Sutter, G. and Casciello, A. and Hausner, T. and Veltroni, Iacopo Ficai and Deppo, Vania Da and Orleański, P. and Nowosielski, Witold and Zawistowski, Tomasz and Szalaı̈, S. and Sodor, B. and Tulyakov, Stepan and Troznai, G. and Banaskiewicz, M. and Bridges, J. C. and Byrne, Shane and Debei, S. and El‐Maarry, M. R. and Hauber, Ernst and Hansen, C. J. and Ivanov, A. B. and Keszthelyi, L. and Kirk, R. L. and Kuzmin, R. O. and Mangold, N. and Marinangeli, L. and Markiewicz, W. J. and Massironi, Matteo and McEwen, A. S. and Okubo, C. H. and Tornabene, L. L. and Wajer, P. and Wray, J. J.",
    title = "The Colour and Stereo Surface Imaging System (CaSSIS) for the ExoMars Trace Gas Orbiter",
    year = "2017",
    journal = "Space Science Reviews",
    abstract = "The Colour and Stereo Surface Imaging System (CaSSIS) is the main imaging system onboard the European Space Agency’s ExoMars Trace Gas Orbiter (TGO) which was launched on 14 March 2016. CaSSIS is intended to acquire moderately high resolution (4.6 m/pixel) targeted images of Mars at a rate of 10–20 images per day from a roughly circular orbit 400 km above the surface. Each image can be acquired in up to four colours and stereo capability is foreseen by the use of a novel rotation mechanism. A typical product from one image acquisition will be a $9.5\textasciitilde \mbox{km} \times {\sim}45\textasciitilde \mbox{km}$ swath in full colour and stereo in one over-flight of the target thereby reducing atmospheric influences inherent in stereo and colour products from previous high resolution imagers. This paper describes the instrument including several novel technical solutions required to achieve the scientific requirements.",
    url = "https://doi.org/10.1007/s11214-017-0421-1",
    doi = "10.1007/s11214-017-0421-1",
    openalex = "W2282278185",
    references = "doi101016jpss200612003"
}

The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures-ExoMars-Landing sites-Mars rover-Search for life. Astrobiology 17, 471-510.

@article{doi101089ast20161533,
    author = "Vago, Jorge L. and Westall, Francès and Teams, Landing S Pasteur Instrument and Coates, A. J. and Jaumann, R. and Korablev, Oleg and Ciarletti, Valérie and Митрофанов, И. Г. and Josset, Jean‐Luc and Sanctis, M. C. De and Bibring, Jean‐Pierre and Rull, F. and Goesmann, F. and Steininger, H. and Goetz, W. and Brinckerhoff, W. and Szopa, Cyril and Raulin, F. and Westall, Francès and Edwards, Howell G. M. and Whyte, Lyle G. and Fairén, Alberto González and Bibring, Jean‐Pierre and Bridges, J. C. and Hauber, Ernst and Ori, G. G. and Werner, Stéphanie C. and Loizeau, D. and Kuzmin, R. O. and Williams, R. M. E. and Flahaut, J. and Forget, F. and Vago, Jorge L. and Rodionov, D. and Korablev, Oleg and Svedhem, H. and Sefton‐Nash, E. and Kminek, Gerhard and Lorenzoni, L. and Joudrier, Luc and Михайлов, В. С. and Zashchirinskiy, Alexander and Alexashkin, S. N. and Calantropio, F. and Merlo, Andrea and Poulakis, Pantelis and Witasse, Olivier and Bayle, Olivier and Bayón, Silvia and Meierhenrich, Uwe J. and Carter, John and García‐Ruiz, Juan Manuel and Baglioni, P. and Haldemann, A. F. C. and Ball, Andrew and Debus, A. and Lindner, Robert and Haessig, Frédéric and Monteiro, David and Trautner, R. and Voland, Christoph and Rebeyre, Pierre and Goulty, Duncan and Didot, F. and Durrant, Stephen and Zekri, Eric and Koschny, D. and Toni, Andrea De and Visentin, Gianfranco and Zwick, Martin and van Winnendael, M. and Azkarate, Martín and Carreau, Christophe and the ExoMars Project Team",
    title = "Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover",
    year = "2017",
    journal = "Astrobiology",
    abstract = "The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures-ExoMars-Landing sites-Mars rover-Search for life. Astrobiology 17, 471-510.",
    url = "https://doi.org/10.1089/ast.2016.1533",
    doi = "10.1089/ast.2016.1533",
    openalex = "W2738005120",
    references = "doi101016jearscirev201601005, doi101016s0301926800001224, doi101038nature04764, doi101038nature10582, doi10108010409230490460765"
}

In 2012, NASA's Curiosity rover landed on Mars to assess its potential as a habitat for past life and investigate the paleoclimate record preserved by sedimentary rocks inside the ~150-kilometer-diameter Gale impact crater. Geological reconstructions from Curiosity rover data have revealed an ancient, habitable lake environment fed by rivers draining into the crater. We synthesize geochemical and mineralogical data from lake-bed mudstones collected during the first 1300 martian solar days of rover operations in Gale. We present evidence for lake redox stratification, established by depth-dependent variations in atmospheric oxidant and dissolved-solute concentrations. Paleoclimate proxy data indicate that a transition from colder to warmer climate conditions is preserved in the stratigraphy. Finally, a late phase of geochemical modification by saline fluids is recognized.

@article{doi101126scienceaah6849,
    author = "Hurowitz, J. A. and Grotzinger, J. P. and Fischer, Woodward W. and McLennan, S. M. and Milliken, R. E. and Stein, N. and Vasavada, A. R. and Blake, D. F. and Dehouck, E. and Eigenbrode, J. L. and Fairén, Alberto González and Frydenvang, J. and Gellert, R. and Grant, J. A. and Gupta, Sanjeev and Herkenhoff, K. E. and Ming, D. W. and Rampe, E. B. and Schmidt, M. E. and Siebach, K. L. and Stack-Morgan, K. and Sumner, D. Y. and Wiens, R. C.",
    title = "Redox stratification of an ancient lake in Gale crater, Mars",
    year = "2017",
    journal = "Science",
    abstract = "In 2012, NASA's Curiosity rover landed on Mars to assess its potential as a habitat for past life and investigate the paleoclimate record preserved by sedimentary rocks inside the \textasciitilde 150-kilometer-diameter Gale impact crater. Geological reconstructions from Curiosity rover data have revealed an ancient, habitable lake environment fed by rivers draining into the crater. We synthesize geochemical and mineralogical data from lake-bed mudstones collected during the first 1300 martian solar days of rover operations in Gale. We present evidence for lake redox stratification, established by depth-dependent variations in atmospheric oxidant and dissolved-solute concentrations. Paleoclimate proxy data indicate that a transition from colder to warmer climate conditions is preserved in the stratigraphy. Finally, a late phase of geochemical modification by saline fluids is recognized.",
    url = "https://doi.org/10.1126/science.aah6849",
    doi = "10.1126/science.aah6849",
    openalex = "W2620979631",
    references = "doi101016jepsl200906042, doi101130b263281"
}

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

@article{doi101126scienceaaq0131,
    author = "Webster, Christopher R. and Mahaffy, P. R. and Atreya, S. K. and Moores, John E. and Flesch, Gregory J. and Malespin, C. A. and McKay, Christopher P. and Martínez, Germán and Smith, C. L. and Martín‐Torres, Javier and Gomez-Elvira, Javier and Zorzano, María‐Paz and Wong, Michael H. and Trainer, M. G. and Steele, A. and Archer, Doug and Sutter, B. and Coll, Patrice and Freissinet, Caroline and Meslin, Pierre‐Yves and Gough, R. V. and House, Christopher H. and Pavlov, Alexander A. and Eigenbrode, J. L. and Glavin, D. P. and Pearson, John C. and Keymeulen, Didier and Christensen, L. E. and Schwenzer, S. P. and Navarro‐González, R. and Pla‐García, Jorge and Rafkin, Scot and Vicente‐Retortillo, Á. and Kahanpää, Henrik and Viúdez‐Moreiras, Daniel and Smith, M. D. and Harri, Ari‐Matti and Genzer, María and Hassler, Donald M. and Lemmon, M. T. and Crisp, J. A. and Sander, Stanley P. and Zurek, Richard W. and Vasavada, A. R.",
    title = "Background levels of methane in Mars’ atmosphere show strong seasonal variations",
    year = "2018",
    journal = "Science",
    abstract = "Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95\% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (\textasciitilde 7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.",
    url = "https://doi.org/10.1126/science.aaq0131",
    doi = "10.1126/science.aaq0131",
    openalex = "W2806842645",
    references = "doi101126science1165243"
}

The presence of liquid water at the base of the martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft. Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.

@article{doi101126scienceaar7268,
    author = "Orosei, R. and Lauro, Sebastian Emanuel and Pettinelli, Elena and Cicchetti, A. and Coradini, M. and Cosciotti, Barbara and Paolo, Federico Di and Flamini, Enrico and Mattei, Elisabetta and Pajola, M. and Soldovieri, Francesco and Cartacci, M. and Cassenti, Francesco and Frigeri, A. and Giuppi, S. and Martufi, Riccardo and Masdea, A. and Mitri, Giuseppe and Nenna, C. and Noschese, R. and Restano, Marco and Seu, R.",
    title = "Radar evidence of subglacial liquid water on Mars",
    year = "2018",
    journal = "Science",
    abstract = "The presence of liquid water at the base of the martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft. Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.",
    url = "https://doi.org/10.1126/science.aar7268",
    doi = "10.1126/science.aar7268",
    openalex = "W2884720674",
    references = "doi1010160012825295900195, doi1010160165168492901034, doi1010292000je001364, doi1010292006je002745, doi1010292009je003425, doi101098rsta19040024, doi101126science1122165, doi101126science1139672, doi101126science1172466, doi101126scienceaar7268"
}

epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users.

@article{doi101007s1121401805746,
    author = "Lognonné, Philippe and Banerdt, W. B. and Giardini, Domenico and Pike, W. T. and Christensen, Ulrich R. and Laudet, Ph. and de Raucourt, S. and Zweifel, P. and Calcutt, S. B. and Bierwirth, M. and Hurst, K. and Ijpelaan, F. and Umland, Jeffrey W. and Llorca-Cejudo, R. and Larson, S. and García, R. and Kedar, S. and Knapmeyer‐Endrun, Brigitte and Mimoun, D. and Mocquet, A. and Panning, M. P. and Weber, R. C. and Sylvestre-Baron, A. and Pont, G. and Verdier, Nicolas and Kerjean, L. and Facto, Linda and Gharakanian, V. and Feldman, Jason and Hoffman, Tom and Klein, Daniel B. and Klein, Kerry and Onufer, Nicholas and Paredes-Garcia, J. and Petkov, Mihail P. and Willis, J. R. and Smrekar, S. E. and Drilleau, M. and Gabsi, T. and Nebut, T. and Robert, O. and Tillier, S. and Moreau, C. and Parise, Miriam and Aveni, G. and Charef, S. Ben and Bennour, Y. and Camus, T. and Dandonneau, P. A. and Desfoux, C. and Lecomte, B. and Pot, Olivier and Revuz, P. and Mance, D. and tenPierick, J. and Bowles, Neil E. and Charalambous, Constantinos and Delahunty, Aifric and Hurley, J. and Irshad, R. and Liu, Huafeng and Mukherjee, A. and Standley, I. M. and Stott, Alexander and Temple, Joan and Warren, T. and Eberhardt, Michel and Kramer, Aron and Kühne, W. and Miettinen, E.-P. and Monecke, M. and Aicardi, C. and André, M. and Baroukh, Julien and Borrien, A. and Bouisset, A. and Boutte, P. and Brethomé, K. and Brysbaert, C. and Carlier, T. and Deleuze, M. and Desmarres, Jean-Michel and Dilhan, D. and Doucet, Cheryl and Faye, Delphine and Faye-Refalo, N. and Navarro‐González, R. and Imbert, C. and Larigauderie, C. and Locatelli, Elisabetta and Luno, Laure and Meyer, Jan-christian and Mialhe, F. and Mouret, J. M. and Nonon, M. and Pahn, Y. and Paillet, A. and Pasquier, P. and Pérez, Gabriel and Pérez, R.",
    title = "SEIS: Insight’s Seismic Experiment for Internal Structure of Mars",
    year = "2019",
    journal = "Space Science Reviews",
    abstract = "epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users.",
    url = "https://doi.org/10.1007/s11214-018-0574-6",
    doi = "10.1007/s11214-018-0574-6",
    openalex = "W2914713473"
}

Noachian-aged Jezero crater is the only known location on Mars where clear orbital detections of carbonates are found in close proximity to clear fluvio-lacustrine features indicating the past presence of a paleolake; however, it is unclear whether or not the carbonates in Jezero are related to the lacustrine activity. This distinction is critical for evaluating the astrobiological potential of the site, as lacustrine carbonates on Earth are capable of preserving biosignatures at scales that may be detectable by a landed mission like the Mars 2020 rover, which is planned to land in Jezero in February 2021. In this study, we conduct a detailed investigation of the mineralogical and morphological properties of geological units within Jezero crater in order to better constrain the origin of carbonates in the basin and their timing relative to fluvio-lacustrine activity. Using orbital visible/near-infrared hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) along with high resolution imagery and digital elevation models, we identify a distinct carbonate-bearing unit, the “Marginal Carbonates,” located along the inner margin of the crater, near the largest inlet valley and the western delta. Based on their strong carbonate signatures, topographic properties, and location in the crater, we propose that this unit may preserve authigenic lacustrine carbonates, precipitated in the near-shore environment of the Jezero paleolake. Comparison to carbonate deposits from terrestrial closed basin lakes suggests that if the Marginal Carbonates are lacustrine in origin, they could preserve macro- and microscopic biosignatures in microbialite rocks like stromatolites, some of which would likely be detectable by Mars 2020. The Marginal Carbonates may represent just one phase of a complex fluvio-lacustrine history in Jezero crater, as we find that the spectral diversity of the fluvio-lacustrine deposits in the crater is consistent with a long-lived lake system cataloging the deposition and erosion of regional geologic units. Thus, Jezero crater may contain a unique record of the evolution of surface environments, climates, and habitability on early Mars.

@article{doi101016jicarus2019113526,
    author = "Horgan, B. and Anderson, R. B. and Dromart, Gilles and Amador, E. S. and Rice, M. S.",
    title = "The mineral diversity of Jezero crater: Evidence for possible lacustrine carbonates on Mars",
    year = "2019",
    journal = "Icarus",
    abstract = "Noachian-aged Jezero crater is the only known location on Mars where clear orbital detections of carbonates are found in close proximity to clear fluvio-lacustrine features indicating the past presence of a paleolake; however, it is unclear whether or not the carbonates in Jezero are related to the lacustrine activity. This distinction is critical for evaluating the astrobiological potential of the site, as lacustrine carbonates on Earth are capable of preserving biosignatures at scales that may be detectable by a landed mission like the Mars 2020 rover, which is planned to land in Jezero in February 2021. In this study, we conduct a detailed investigation of the mineralogical and morphological properties of geological units within Jezero crater in order to better constrain the origin of carbonates in the basin and their timing relative to fluvio-lacustrine activity. Using orbital visible/near-infrared hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) along with high resolution imagery and digital elevation models, we identify a distinct carbonate-bearing unit, the “Marginal Carbonates,” located along the inner margin of the crater, near the largest inlet valley and the western delta. Based on their strong carbonate signatures, topographic properties, and location in the crater, we propose that this unit may preserve authigenic lacustrine carbonates, precipitated in the near-shore environment of the Jezero paleolake. Comparison to carbonate deposits from terrestrial closed basin lakes suggests that if the Marginal Carbonates are lacustrine in origin, they could preserve macro- and microscopic biosignatures in microbialite rocks like stromatolites, some of which would likely be detectable by Mars 2020. The Marginal Carbonates may represent just one phase of a complex fluvio-lacustrine history in Jezero crater, as we find that the spectral diversity of the fluvio-lacustrine deposits in the crater is consistent with a long-lived lake system cataloging the deposition and erosion of regional geologic units. Thus, Jezero crater may contain a unique record of the evolution of surface environments, climates, and habitability on early Mars.",
    url = "https://doi.org/10.1016/j.icarus.2019.113526",
    doi = "10.1016/j.icarus.2019.113526",
    openalex = "W2986677734",
    references = "doi1010073540323449, doi1010079783642523359, doi101007s1034701604846, doi101016jearscirev200810005, doi101016jicarus200806016, doi1010291998je000540, doi1010292006je002808, doi101146annurevearth042711105327, doi101146annurevearth060313055024, doi103389fbioe201600004"
}

Executive Summary Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re‐evaluate and update the sample‐related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub‐objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub‐Objectives for MSR Identified by iMOST Objective 1 Interpret the primary geologic processes and history that formed the Martian geologic record, with an emphasis on the role of water. Intent To investigate the geologic environment(s) represented at the Mars 2020 landing site, provide definitive geologic context for collected samples, and detail any characteristics that might relate to past biologic processes This objective is divided into five sub‐objectives that would apply at different landing sites. Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks. Intent To understand the preserved Martian sedimentary record. Samples A suite of sedimentary rocks that span the range of variation. Importance Basic inputs into the history of water, climate change, and the possibility of life Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression. Intent To evaluate at least one potentially life‐bearing “habitable” environment Samples A suite of rocks formed and/or altered by hydrothermal fluids. Importance Identification of a potentially habitable geochemical environment with high preservation potential. Understand the rocks and minerals representative of a deep subsurface groundwater environment. Intent To evaluate definitively the role of water in the subsurface. Samples Suites of rocks/veins representing water/rock interaction in the subsurface. Importance May constitute the longest‐lived habitable environments and a key to the hydrologic cycle. Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time. Intent To constrain time‐variable factors necessary to preserve records of microbial life. Samples Regolith, paleosols, and evaporites. Importance Subaerial near‐surface processes could support and preserve microbial life. Determine the petrogenesis of Martian igneous rocks in time and space. Intent To provide definitive characterization of igneous rocks on Mars. Samples Diverse suites of ancient igneous rocks. Importance Thermochemical record of the planet and nature of the interior. Objective 2 Assess and interpret the potential biological history of Mars, including assaying returned samples for the evidence of life. Intent To investigate the nature and extent of Martian habitability, the conditions and processes that supported or challenged life, how different environments might have influenced the preservation of biosignatures and created nonbiological “mimics,” and to look for biosignatures of past or present life. This objective has three sub‐objectives: Assess and characterize carbon, including possible organic and pre‐biotic chemistry. Samples All samples collected as part of Objective 1. Importance Any biologic molecular scaffolding on Mars would likely be carbon‐based. Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures. Samples All samples collected as part of Objective 1. Importance Provides the means of discovering ancient life. Assess the possibility that any life forms detected are alive, or were recently alive. Samples All samples collected as part of Objective 1. Importance Planetary protection, and arguably the most important scientific discovery possible. Objective 3 Quantitatively determine the evolutionary timeline of Mars. Intent To provide a radioisotope‐based time scale for major events, including magmatic, tectonic, fluvial, and impact events, and the formation of major sedimentary deposits and geomorphological features. Samples Ancient igneous rocks that bound critical stratigraphic intervals or correlate with crater‐dated surfaces.

@article{doi101111maps13242,
    author = "Beaty, D. W. and Grady, M. M. and McSween, H. Y. and Sefton‐Nash, E. and Carrier, Brandi L. and Altieri, Francesca and Amelin, Y. and Ammannito, E. and Anand, M. and Benning, Liane G. and Bishop, J. L. and Borg, L. E. and Boucher, Dale and Brucato, J. R. and Busemann, H. and Campbell, Kathleen A. and Czaja, Andrew D. and Debaille, Vinciane and Marais, David J. Des and Dixon, Mike and Ehlmann, B. L. and Farmer, Jack D. and Fernández‐Remolar, David C. and Filiberto, J. and Fogarty, J. and Glavin, D. P. and Goreva, Y. S. and Hallis, L. J. and Harrington, A. D. and Hausrath, Elisabeth M. and Herd, C. D. K. and Horgan, B. and Humayun, M. and Kleine, T. and Kleinhenz, Julie and Mackelprang, Rachel and Mangold, N. and Mayhew, L. E. and McCoy, J. T. and McCubbin, F. M. and McLennan, S. M. and Moser, D. E. and Moynier, Frédéric and Mustard, John F. and Niles, P. B. and Ori, G. G. and Raulin, F. and Rettberg, Petra and Rucker, Michelle A. and Schmitz, Nicole and Schwenzer, S. P. and Sephton, Mark A. and Shaheen, R. and Sharp, Z. D. and Shuster, David L. and Siljeström, Sandra and Smith, C. L. and Spry, J. Andy and Steele, A. and Swindle, T. D. and ten Kate, I. L. and Tosca, Nicholas J. and Usui, Tomohiro and Kranendonk, Martin J. Van and Wadhwa, M. and Weiss, B. P. and Werner, Stéphanie C. and Westall, Francès and Wheeler, Raymond M. and Zipfel, J. and Zorzano, María‐Paz",
    title = "The potential science and engineering value of samples delivered to Earth by Mars sample return",
    year = "2019",
    journal = "Meteoritics and Planetary Science",
    abstract = "Executive Summary Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re‐evaluate and update the sample‐related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub‐objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub‐Objectives for MSR Identified by iMOST Objective 1 Interpret the primary geologic processes and history that formed the Martian geologic record, with an emphasis on the role of water. Intent To investigate the geologic environment(s) represented at the Mars 2020 landing site, provide definitive geologic context for collected samples, and detail any characteristics that might relate to past biologic processes This objective is divided into five sub‐objectives that would apply at different landing sites. Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks. Intent To understand the preserved Martian sedimentary record. Samples A suite of sedimentary rocks that span the range of variation. Importance Basic inputs into the history of water, climate change, and the possibility of life Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression. Intent To evaluate at least one potentially life‐bearing “habitable” environment Samples A suite of rocks formed and/or altered by hydrothermal fluids. Importance Identification of a potentially habitable geochemical environment with high preservation potential. Understand the rocks and minerals representative of a deep subsurface groundwater environment. Intent To evaluate definitively the role of water in the subsurface. Samples Suites of rocks/veins representing water/rock interaction in the subsurface. Importance May constitute the longest‐lived habitable environments and a key to the hydrologic cycle. Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time. Intent To constrain time‐variable factors necessary to preserve records of microbial life. Samples Regolith, paleosols, and evaporites. Importance Subaerial near‐surface processes could support and preserve microbial life. Determine the petrogenesis of Martian igneous rocks in time and space. Intent To provide definitive characterization of igneous rocks on Mars. Samples Diverse suites of ancient igneous rocks. Importance Thermochemical record of the planet and nature of the interior. Objective 2 Assess and interpret the potential biological history of Mars, including assaying returned samples for the evidence of life. Intent To investigate the nature and extent of Martian habitability, the conditions and processes that supported or challenged life, how different environments might have influenced the preservation of biosignatures and created nonbiological “mimics,” and to look for biosignatures of past or present life. This objective has three sub‐objectives: Assess and characterize carbon, including possible organic and pre‐biotic chemistry. Samples All samples collected as part of Objective 1. Importance Any biologic molecular scaffolding on Mars would likely be carbon‐based. Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures. Samples All samples collected as part of Objective 1. Importance Provides the means of discovering ancient life. Assess the possibility that any life forms detected are alive, or were recently alive. Samples All samples collected as part of Objective 1. Importance Planetary protection, and arguably the most important scientific discovery possible. Objective 3 Quantitatively determine the evolutionary timeline of Mars. Intent To provide a radioisotope‐based time scale for major events, including magmatic, tectonic, fluvial, and impact events, and the formation of major sedimentary deposits and geomorphological features. Samples Ancient igneous rocks that bound critical stratigraphic intervals or correlate with crater‐dated surfaces.",
    url = "https://doi.org/10.1111/maps.13242",
    doi = "10.1111/maps.13242",
    openalex = "W2922358052",
    references = "doi101016jicarus201712046, doi101016jprecamres201308001, doi101111maps12639, doi101111sed12205, doi101126scienceaar7268, doi101130g398221"
}

family. The dynamic nature of these lakes appears to influence the biological, biochemical, and geological components of the ecosystem to a large effect. Inter- and intra-lake variations in the distributions of microbial communities were significant, and could only to a minor degree be explained by underlying environmental conditions. The communities are likely significantly influenced by small scale local effects caused by variations in geological settings and dynamic interactions caused by aeolian transport and flooding and evaporation events.

@article{doi103389fmicb201900779,
    author = "Aerts, Joost W. and van Spanning, Rob J. M. and Flahaut, J. and Molenaar, Douwe and Bland, P. A. and Genge, Matt J. and Ehrenfreund, P. and Martins, Zita",
    title = "Microbial Communities in Sediments From Four Mildly Acidic Ephemeral Salt Lakes in the Yilgarn Craton (Australia) – Terrestrial Analogs to Ancient Mars",
    year = "2019",
    journal = "Frontiers in Microbiology",
    abstract = "family. The dynamic nature of these lakes appears to influence the biological, biochemical, and geological components of the ecosystem to a large effect. Inter- and intra-lake variations in the distributions of microbial communities were significant, and could only to a minor degree be explained by underlying environmental conditions. The communities are likely significantly influenced by small scale local effects caused by variations in geological settings and dynamic interactions caused by aeolian transport and flooding and evaporation events.",
    url = "https://doi.org/10.3389/fmicb.2019.00779",
    doi = "10.3389/fmicb.2019.00779",
    openalex = "W2944699685",
    references = "doi101126scienceaar7268"
}

@article{doi101007s1121402000762y,
    author = "Farley, Kenneth A. and Williford, Kenneth H. and Stack, K. M. and Bhartia, R. and Chen, Al and de la Torre, M. and Hand, K. P. and Goreva, Y. S. and Herd, C. D. K. and Hueso, R. and Liu, Yang and Maki, J. N. and Martínez, Germán and Moeller, R. and Nelessen, Adam and Newman, Claire and Nunes, D. C. and Ponce, Adrian and Spanovich, N. and Willis, Peter A. and Beegle, L. W. and Bell, J. F. and Brown, A. J. and Hamran, S. E. and Hurowitz, J. A. and Maurice, S. and Paige, D. A. and Rodríguez‐Manfredi, J. A. and Schulte, M. and Wiens, R. C.",
    title = "Mars 2020 Mission Overview",
    year = "2020",
    journal = "Space Science Reviews",
    url = "https://doi.org/10.1007/s11214-020-00762-y",
    doi = "10.1007/s11214-020-00762-y",
    openalex = "W3110256918",
    references = "doi10100797894017103505, doi101016jepsl200906042, doi101016jicarus200806016, doi101038nature04764"
}

@article{doi101016jchemer2020125605,
    author = "Rampe, E. B. and Blake, D. F. and Bristow, T. F. and Ming, D. W. and Vaniman, D. T. and Morris, R. V. and Achilles, C. N. and Chipera, S. J. and Morrison, Shaunna M. and Tu, Valerie and Yen, A. S. and Castle, N. and Downs, G. W. and Downs, Robert T. and Grotzinger, J. P. and Hazen, Robert M. and Treiman, A. H. and Peretyazhko, T. and Marais, David J. Des and Walroth, Richard C. and Craig, Patricia and Crisp, J. A. and Lafuente, B. and Morookian, John Michael and Sarrazin, P. and Thorpe, M. T. and Bridges, J. C. and Edgar, L. A. and Fedo, Christopher M. and Freissinet, Caroline and Gellert, R. and Mahaffy, P. R. and Newsom, H. E. and Johnson, J. R. and Kah, Linda C. and Siebach, K. L. and Schieber, Jüergen and Sun, V. Z. and Vasavada, A. R. and Wellington, Danika and Wiens, R. C.",
    title = "Mineralogy and geochemistry of sedimentary rocks and eolian sediments in Gale crater, Mars: A review after six Earth years of exploration with Curiosity",
    year = "2020",
    journal = "Geochemistry",
    url = "https://doi.org/10.1016/j.chemer.2020.125605",
    doi = "10.1016/j.chemer.2020.125605",
    openalex = "W3002486190",
    references = "doi101146annurevearth060313055024"
}

The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission began collecting high quality seismic data on Mars in February 2019. This manuscript documents the seismicity observed by SEIS, InSight's seismometer, from this time until the end of March 2020. Within the InSight project, the Marsquake Service (MQS) is responsible for prompt review of all seismic data collected by InSight, detection of events that are likely to be of seismic origin, and curation and release of seismic catalogues. In the first year of data collection, MQS have identified 465 seismic events that we interpret to be from regional and teleseismic marsquakes. Seismic events are grouped into 2 different event families: the low frequency family is dominated by energy at long period below 1 s, and the high frequency family primarily include energy at and above 2.4 Hz. Event magnitudes, from Mars-specific scales, range from 1.3 to 3.7. A third class of events with very short duration but high frequency bursts have been observed 712 times. These are likely associated with a local source driven by thermal stresses. This paper describes the data collected so far in the mission and the procedures under which MQS operates; summarises the content of the current MQS seismic catalogue; and presents the key features of the events we have observed so far, using the largest events as examples.

@article{doi101016jpepi2020106595,
    author = "Clinton, John and Ceylan, Savas and van Driel, Martin and Giardini, Domenico and Stähler, Simon C. and Böse, Maren and Charalambous, Constantinos and Dahmen, Nikolaj and Horleston, Anna and Kawamura, Taïchi and Khan, A. and Orhand‐Mainsant, G. and Scholz, John‐Robert and Euchner, F. and Banerdt, W. B. and Lognonné, Philippe and Banfield, D. and Beucler, É. and García, R. and Kedar, S. and Panning, M. P. and Perrin, C. and Pike, W. T. and Smrekar, S. E. and Spiga, Aymeric and Stott, Alexander",
    title = "The Marsquake catalogue from InSight, sols 0–478",
    year = "2020",
    journal = "Physics of The Earth and Planetary Interiors",
    abstract = "The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission began collecting high quality seismic data on Mars in February 2019. This manuscript documents the seismicity observed by SEIS, InSight's seismometer, from this time until the end of March 2020. Within the InSight project, the Marsquake Service (MQS) is responsible for prompt review of all seismic data collected by InSight, detection of events that are likely to be of seismic origin, and curation and release of seismic catalogues. In the first year of data collection, MQS have identified 465 seismic events that we interpret to be from regional and teleseismic marsquakes. Seismic events are grouped into 2 different event families: the low frequency family is dominated by energy at long period below 1 s, and the high frequency family primarily include energy at and above 2.4 Hz. Event magnitudes, from Mars-specific scales, range from 1.3 to 3.7. A third class of events with very short duration but high frequency bursts have been observed 712 times. These are likely associated with a local source driven by thermal stresses. This paper describes the data collected so far in the mission and the procedures under which MQS operates; summarises the content of the current MQS seismic catalogue; and presents the key features of the events we have observed so far, using the largest events as examples.",
    url = "https://doi.org/10.1016/j.pepi.2020.106595",
    doi = "10.1016/j.pepi.2020.106595",
    openalex = "W3094160404",
    references = "doi101038s415610200544y"
}

Abstract Vera Rubin ridge (VRR) is an erosion‐resistant feature on the northwestern slope of Mount Sharp in Gale crater, Mars, and orbital visible/shortwave infrared measurements indicate it contains red hematite. The Mars Science Laboratory Curiosity rover performed an extensive campaign on VRR to study its mineralogy, geochemistry, and sedimentology to determine the depositional and diagenetic history of the ridge and constrain the processes by which the hematite could have formed. X‐ray diffraction (XRD) data from the CheMin instrument of four samples drilled on and below VRR demonstrate differences in iron, phyllosilicate, and sulfate mineralogy and hematite grain size. Hematite is common across the ridge, and its detection in a gray outcrop suggest localized regions with coarse‐grained hematite, which commonly forms from warm fluids. Broad XRD peaks for hematite in one sample below VRR and the abundance of FeO T in the amorphous component suggest the presence of nanocrystalline hematite and amorphous Fe oxides/oxyhydroxides. Well crystalline akaganeite and jarosite are present in two samples drilled from VRR, indicating at least limited alteration by acid‐saline fluids. Collapsed nontronite is present below VRR, but samples from VRR contain phyllosilicate with d(001) = 9.6 Å, possibly from ferripyrophyllite or an acid‐altered smectite. The most likely cementing agents creating the ridge are hematite and opaline silica. We hypothesize late diagenesis can explain much of the mineralogical variation on the ridge, where multiple fluid episodes with variable pH, salinity, and temperature altered the rocks, causing the precipitation and crystallization of phases that are not otherwise in equilibrium.

@article{doi1010292019je006306,
    author = "Rampe, E. B. and Bristow, T. F. and Morris, R. V. and Morrison, Shaunna M. and Achilles, C. N. and Ming, D. W. and Vaniman, D. T. and Blake, D. F. and Tu, Valerie and Chipera, S. J. and Yen, A. S. and Peretyazhko, T. and Downs, Robert T. and Hazen, Robert M. and Treiman, A. H. and Grotzinger, J. P. and Castle, N. and Craig, Patricia and Marais, David J. Des and Thorpe, M. T. and Walroth, Richard C. and Downs, G. W. and Fraeman, A. A. and Siebach, K. L. and Gellert, R. and Lafuente, B. and McAdam, A. C. and Meslin, Pierre‐Yves and Sutter, B. and Salvatore, M. R.",
    title = "Mineralogy of Vera Rubin Ridge From the Mars Science Laboratory CheMin Instrument",
    year = "2020",
    journal = "Journal of Geophysical Research Planets",
    abstract = "Abstract Vera Rubin ridge (VRR) is an erosion‐resistant feature on the northwestern slope of Mount Sharp in Gale crater, Mars, and orbital visible/shortwave infrared measurements indicate it contains red hematite. The Mars Science Laboratory Curiosity rover performed an extensive campaign on VRR to study its mineralogy, geochemistry, and sedimentology to determine the depositional and diagenetic history of the ridge and constrain the processes by which the hematite could have formed. X‐ray diffraction (XRD) data from the CheMin instrument of four samples drilled on and below VRR demonstrate differences in iron, phyllosilicate, and sulfate mineralogy and hematite grain size. Hematite is common across the ridge, and its detection in a gray outcrop suggest localized regions with coarse‐grained hematite, which commonly forms from warm fluids. Broad XRD peaks for hematite in one sample below VRR and the abundance of FeO T in the amorphous component suggest the presence of nanocrystalline hematite and amorphous Fe oxides/oxyhydroxides. Well crystalline akaganeite and jarosite are present in two samples drilled from VRR, indicating at least limited alteration by acid‐saline fluids. Collapsed nontronite is present below VRR, but samples from VRR contain phyllosilicate with d(001) = 9.6 Å, possibly from ferripyrophyllite or an acid‐altered smectite. The most likely cementing agents creating the ridge are hematite and opaline silica. We hypothesize late diagenesis can explain much of the mineralogical variation on the ridge, where multiple fluid episodes with variable pH, salinity, and temperature altered the rocks, causing the precipitation and crystallization of phases that are not otherwise in equilibrium.",
    url = "https://doi.org/10.1029/2019je006306",
    doi = "10.1029/2019je006306",
    openalex = "W3037842049",
    references = "doi1010160009254176900012, doi101038s415610200544y"
}

@article{doi101038s4155002012006,
    author = "Lauro, Sebastian Emanuel and Pettinelli, Elena and Caprarelli, Graziella and Guallini, Luca and Rossi, Angelo Pio and Mattei, Elisabetta and Cosciotti, Barbara and Cicchetti, Andrea and Soldovieri, Francesco and Cartacci, Marco and Paolo, Federico Di and Noschese, Raffaella and Orosei, Roberto",
    title = "Multiple subglacial water bodies below the south pole of Mars unveiled by new MARSIS data",
    year = "2020",
    journal = "Nature Astronomy",
    url = "https://doi.org/10.1038/s41550-020-1200-6",
    doi = "10.1038/s41550-020-1200-6",
    openalex = "W3091133455",
    references = "doi101126scienceaar7268"
}

@article{doi101038s4156102005340,
    author = "Banfield, D. and Spiga, Aymeric and Newman, Claire and Forget, F. and Lemmon, M. T. and Lorenz, R. D. and Murdoch, Naomi and Viúdez‐Moreiras, Daniel and Pla‐García, Jorge and García, R. and Lognonné, Philippe and Karatekin, Özgür and Perrin, C. and Martire, Léo and Teanby, N. A. and Hove, Bart Van and Maki, J. N. and Kenda, B. and Mueller, Nils and Rodríguez, S. and Kawamura, Taïchi and McClean, John and Stott, Alexander and Charalambous, Constantinos and Millour, Ehouarn and Johnson, C. L. and Mittelholz, Anna and Määttänen, Anni and Lewis, S. R. and Clinton, John and Stähler, Simon C. and Ceylan, Savas and Giardini, Domenico and Warren, T. and Pike, W. T. and Daubar, I. J. and Golombek, M. P. and Rolland, Lucie and Widmer‐Schnidrig, Rudolf and Mimoun, D. and Beucler, É. and Jacob, A. W. B. and Łucas, Antoine and Baker, Mariah and Ansan, V. and Hurst, K. and Mora‐Sotomayor, Luis and Navarro, Sara and Torres, J. and Lepinette, A. and Molina, A. and Marín, M. and Gómez‐Elvira, Javier and Peinado, V. and Rodríguez‐Manfredi, J. A. and Carcich, B. and Sackett, Stephen S. and Russell, Christopher and Spohn, Tilman and Smrekar, S. E. and Banerdt, W. B.",
    title = "The atmosphere of Mars as observed by InSight",
    year = "2020",
    journal = "Nature Geoscience",
    url = "https://doi.org/10.1038/s41561-020-0534-0",
    doi = "10.1038/s41561-020-0534-0",
    openalex = "W3007080254",
    references = "doi101038s415610200544y"
}

Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles. The crust beneath the InSight lander on Mars is altered or fractured to 8–11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight’s seismometer.

@article{doi101038s415610200536y,
    author = "Lognonné, Philippe and Banerdt, W. B. and Pike, W. T. and Giardini, Domenico and Christensen, Ulrich R. and García, R. and Kawamura, Taïchi and Kedar, S. and Knapmeyer‐Endrun, Brigitte and Margerin, Ludovic and Nimmo, F. and Panning, M. P. and Tauzin, Benoît and Scholz, John‐Robert and Antonangeli, Daniele and Barkaoui, Salma and Beucler, É. and Bissig, Felix and Brinkman, Nienke and Calvet, Marie and Ceylan, Savas and Charalambous, Constantinos and Davis, Paul M. and van Driel, Martin and Drilleau, M. and Fayon, Lucile and Joshi, Rakshit and Kenda, B. and Khan, Amir and Knapmeyer, Martin and Lekić, V. and McClean, John and Mimoun, D. and Murdoch, Naomi and Pan, Lu and Perrin, C. and Pinot, Baptiste and Pou, L. and Ménina, Sabrina and Rodríguez, S. and Schmelzbach, Cédric and Schmerr, N. C. and Sollberger, David and Spiga, Aymeric and Stähler, Simon C. and Stott, Alexander and Stutzmann, É. and Tharimena, Saikiran and Widmer‐Schnidrig, Rudolf and Андерссон, Фредрик and Ansan, V. and Beghein, Caroline and Böse, Maren and Bozdağ, E. and Clinton, John and Daubar, I. J. and Delage, Pierre and Fuji, Nobuaki and Golombek, M. P. and Grott, Matthias and Horleston, Anna and Hurst, K. and Irving, J. C. E. and Jacob, A. W. B. and Knollenberg, J. and Krasner, Sanford and Krause, C. and Lorenz, R. D. and Michaut, Chloé and Myhill, Robert and Nissen‐Meyer, Tarje and ten Pierick, Jan and Plesa, Ana‐Catalina and Quantin‐Nataf, Cathy and Robertsson, Johan O. A. and Rochas, L. and Schimmel, Martín and Smrekar, S. E. and Spohn, Tilman and Teanby, N. A. and Tromp, Jeroen and Vallade, Julien and Verdier, Nicolas and Vrettos, Christos and Weber, R. C. and Banfield, D. and Barrett, Elizabeth Ann and Bierwirth, M. and Calcutt, S. B. and Compaire, Nicolas and Johnson, C. L. and Mance, D. and Euchner, F. and Kerjean, L. and Mainsant, G. and Mocquet, A. and Rodríguez‐Manfredi, J. A. and Pont, G. and Laudet, Ph. and Nebut, T.",
    title = "Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data",
    year = "2020",
    journal = "Nature Geoscience",
    abstract = "Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles. The crust beneath the InSight lander on Mars is altered or fractured to 8–11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight’s seismometer.",
    url = "https://doi.org/10.1038/s41561-020-0536-y",
    doi = "10.1038/s41561-020-0536-y",
    openalex = "W3008551921",
    references = "doi101038s415610200544y"
}

The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019. The mission aims to detect, characterize and locate seismic activity on Mars, and to further constrain the internal structure, composition and dynamics of the planet. Here, we present seismometer data recorded until 30 September 2019, which reveal that Mars is seismically active. We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude Mw 3–4 with waves propagating at various depths in the mantle. These marsquakes have spectral characteristics similar to the seismicity observed on the Earth and Moon. We determine that two of the largest detected marsquakes were located near the Cerberus Fossae fracture system. From the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-S-wave-velocity layer in the upper mantle. Mars is seismically active: 24 subcrustal magnitude 3–4 marsquakes and 150 smaller events have been identified up to 30 September 2019, by an analysis of seismometer data from the InSight lander.

@article{doi101038s4156102005398,
    author = "Giardini, Domenico and Lognonné, Philippe and Banerdt, W. B. and Pike, W. T. and Christensen, Ulrich R. and Ceylan, Savas and Clinton, John and van Driel, Martin and Stähler, Simon C. and Böse, Maren and García, R. and Khan, A. and Panning, M. P. and Perrin, C. and Banfield, D. and Beucler, É. and Charalambous, Constantinos and Euchner, F. and Horleston, Anna and Jacob, A. W. B. and Kawamura, Taïchi and Kedar, S. and Mainsant, G. and Scholz, John‐Robert and Smrekar, S. E. and Spiga, Aymeric and Agard, Christophe and Antonangeli, Daniele and Barkaoui, Salma and Barrett, Elizabeth Ann and Combes, P. and Conejero, Vincent and Daubar, I. J. and Drilleau, M. and Ferrier, C. and Gabsi, T. and Гудкова, Т. В. and Hurst, K. and Karakostas, Foivos and King, Scott D. and Knapmeyer, Martin and Knapmeyer‐Endrun, Brigitte and Llorca-Cejudo, R. and Łucas, Antoine and Luno, Laure and Margerin, Ludovic and McClean, John and Mimoun, D. and Murdoch, Naomi and Nimmo, F. and Nonon, M. and Pardo, Constanza and Rivoldini, Attilio and Rodríguez‐Manfredi, J. A. and Samuel, Henri and Schimmel, Martín and Stott, Alexander and Stutzmann, É. and Teanby, N. A. and Warren, T. and Weber, R. C. and Wieczorek, M. A. and Yana, Charles",
    title = "The seismicity of Mars",
    year = "2020",
    journal = "Nature Geoscience",
    abstract = "The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019. The mission aims to detect, characterize and locate seismic activity on Mars, and to further constrain the internal structure, composition and dynamics of the planet. Here, we present seismometer data recorded until 30 September 2019, which reveal that Mars is seismically active. We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude Mw 3–4 with waves propagating at various depths in the mantle. These marsquakes have spectral characteristics similar to the seismicity observed on the Earth and Moon. We determine that two of the largest detected marsquakes were located near the Cerberus Fossae fracture system. From the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-S-wave-velocity layer in the upper mantle. Mars is seismically active: 24 subcrustal magnitude 3–4 marsquakes and 150 smaller events have been identified up to 30 September 2019, by an analysis of seismometer data from the InSight lander.",
    url = "https://doi.org/10.1038/s41561-020-0539-8",
    doi = "10.1038/s41561-020-0539-8",
    openalex = "W3006706642",
    references = "doi101038s415610200544y"
}

NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude Mw = 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately Mw = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding Mw = 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander. Geophysical and meteorological measurements by NASA’s InSight lander on Mars reveal a planet that is seismically active and provide information about the interior, surface and atmospheric workings of Mars.

@article{doi101038s415610200544y,
    author = "Banerdt, W. B. and Smrekar, S. E. and Banfield, D. and Giardini, Domenico and Golombek, M. P. and Johnson, C. L. and Lognonné, Philippe and Spiga, Aymeric and Spohn, Tilman and Perrin, C. and Stähler, Simon C. and Antonangeli, Daniele and Asmar, S. W. and Beghein, Caroline and Bowles, Neil E. and Bozdağ, E. and Chi, Peter and Christensen, Ulrich R. and Clinton, John and Collins, G. S. and Daubar, I. J. and Dehant, V. and Drilleau, M. and Fillingim, Matthew and Folkner, W. M. and García, R. and Garvin, J. B. and Grant, J. A. and Grott, Matthias and Grygorczuk, Jerzy and Hudson, T. L. and Irving, J. C. E. and Kargl, G. and Kawamura, Taïchi and Kedar, S. and King, Scott D. and Knapmeyer‐Endrun, Brigitte and Knapmeyer, Martin and Lemmon, M. T. and Lorenz, R. D. and Maki, J. N. and Margerin, Ludovic and McLennan, S. M. and Michaut, Chloé and Mimoun, D. and Mittelholz, Anna and Mocquet, A. and Morgan, Paul and Mueller, Nils and Murdoch, Naomi and Nagihara, S. and Newman, Claire and Nimmo, F. and Panning, M. P. and Pike, W. T. and Plesa, Ana-Catalina and Rodríguez, S. and Rodríguez‐Manfredi, J. A. and Russell, C. T. and Schmerr, N. C. and Siegler, M.A. and Stanley, S. and Stutzmann, É. and Teanby, N. A. and Tromp, Jeroen and van Driel, Martin and Warner, N. H. and Weber, R. C. and Wieczorek, M. A.",
    title = "Initial results from the InSight mission on Mars",
    year = "2020",
    journal = "Nature Geoscience",
    abstract = "NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude Mw = 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately Mw = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding Mw = 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander. Geophysical and meteorological measurements by NASA’s InSight lander on Mars reveal a planet that is seismically active and provide information about the interior, surface and atmospheric workings of Mars.",
    url = "https://doi.org/10.1038/s41561-020-0544-y",
    doi = "10.1038/s41561-020-0544-y",
    openalex = "W3008984412",
    references = "doi101006icar20026921, doi101007s1121401603219, doi101007s1121401805746, doi101016jpepi201204002, doi1010292000je001364, doi101038s4156102005340, doi101038s415610200536y, doi101038s4156102005398, doi101126science2845415790, doi104401ag3472"
}

To assess Mars’ potential for both harboring life and providing useable resources for future human exploration, it is of paramount importance to comprehend the water situation on the planet. Therefore, studies have been conducted to determine any evidence of past or present water existence on Mars. While the presence of abundant water on Mars very early in its history is widely accepted, on its modern form, only a fraction of this water can be found, as either ice or locked into the structure of Mars’ plentiful water-rich materials. Water on the planet is evaluated through various evidence such as rocks and minerals, Martian achondrites, low volume transient briny outflows (e.g., dune flows, reactivated gullies, slope streaks, etc.), diurnal shallow soil moisture (e.g., measurements by Curiosity and Phoenix Lander), geomorphic representation (possibly from lakes and river valleys), and groundwater, along with further evidence obtained by probe and rover discoveries. One of the most significant lines of evidence is for an ancient streambed in Gale Crater, implying ancient amounts of “vigorous” water on Mars. Long ago, hospitable conditions for microbial life existed on the surface of Mars, as it was likely periodically wet. However, its current dry surface makes it almost impossible as an appropriate environment for living organisms; therefore, scientists have recognized the planet’s subsurface environments as the best potential locations for exploring life on Mars. As a result, modern research has aimed towards discovering underground water, leading to the discovery of a large amount of underground ice in 2016 by NASA, and a subglacial lake in 2018 by Italian scientists. Nevertheless, the presence of life in Mars’ history is still an open question. In this unifying context, the current review summarizes results from a wide variety of studies and reports related to the history of water on Mars, as well as any related discussions on the possibility of living organism existence on the planet.

@article{doi103390galaxies8020040,
    author = "Nazari‐Sharabian, Mohammad and Aghababaei, Mohammad and Karakouzian, Moses and Karami, Mehrdad",
    title = "Water on Mars—A Literature Review",
    year = "2020",
    journal = "Galaxies",
    abstract = "To assess Mars’ potential for both harboring life and providing useable resources for future human exploration, it is of paramount importance to comprehend the water situation on the planet. Therefore, studies have been conducted to determine any evidence of past or present water existence on Mars. While the presence of abundant water on Mars very early in its history is widely accepted, on its modern form, only a fraction of this water can be found, as either ice or locked into the structure of Mars’ plentiful water-rich materials. Water on the planet is evaluated through various evidence such as rocks and minerals, Martian achondrites, low volume transient briny outflows (e.g., dune flows, reactivated gullies, slope streaks, etc.), diurnal shallow soil moisture (e.g., measurements by Curiosity and Phoenix Lander), geomorphic representation (possibly from lakes and river valleys), and groundwater, along with further evidence obtained by probe and rover discoveries. One of the most significant lines of evidence is for an ancient streambed in Gale Crater, implying ancient amounts of “vigorous” water on Mars. Long ago, hospitable conditions for microbial life existed on the surface of Mars, as it was likely periodically wet. However, its current dry surface makes it almost impossible as an appropriate environment for living organisms; therefore, scientists have recognized the planet’s subsurface environments as the best potential locations for exploring life on Mars. As a result, modern research has aimed towards discovering underground water, leading to the discovery of a large amount of underground ice in 2016 by NASA, and a subglacial lake in 2018 by Italian scientists. Nevertheless, the presence of life in Mars’ history is still an open question. In this unifying context, the current review summarizes results from a wide variety of studies and reports related to the history of water on Mars, as well as any related discussions on the possibility of living organism existence on the planet.",
    url = "https://doi.org/10.3390/galaxies8020040",
    doi = "10.3390/galaxies8020040",
    openalex = "W3023166381",
    references = "doi101126scienceaar7268"
}

Abstract On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2–7 m, while providing data at sub-mm to mm scales. We report on SuperCam’s science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.

@article{doi101007s1121402100807w,
    author = "Maurice, S. and Wiens, R. C. and Bernardi, P. and Caïs, Ph. and Robinson, S. and Nelson, T. and Gasnault, O. and Réess, Jean-Michel and Deleuze, M. and Rull, F. and Manrique, J. A. and Abbaki, S. and Anderson, R. B. and André, Y. and Angel, S. Michael and Arana, Gorka and Battault, T. and Beck, Pierre and Benzerara, Karim and Bernard, Sylvain and Berthias, J. P. and Beyssac, Olivier and Bonafous, Marion and Bousquet, Bruno and Boutillier, Mathieu and Cadu, Alexandre and Castro, Kepa and Chapron, F. and Chide, Baptiste and Clark, Kenneth P. and Clavé, Elise and Clegg, S. M. and Cloutis, E. A. and Collin, C. and Córdoba-Lanús, Elizabeth and Cousin, A. and Dameury, J.-C. and D’anna, Willy and Daydou, Y. and Debus, A. and DeFlores, Lauren and Dehouck, E. and Delapp, D. and de los Santos, G. and Donny, Christophe and Doressoundiram, A. and Dromart, Gilles and Dubois, Bruno and Dufour, Arnaud and Dupieux, M. and Egan, Miles J. and Ervin, Joan and Fabre, C. and Fau, A. and Fischer, Woodward W. and Forni, O. and Fouchet, Thierry and Frydenvang, J. and Gauffre, S. and Gauthier, M. and Gharakanian, V. and Gilard, O. and Gontijo, I. and Navarro‐González, R. and Granena, David and Grotzinger, J. P. and Hassen‐Khodja, Réda and Heim, Marina and Hello, Y. and Hervet, Gilles and Humeau, Olivier and Jacob, Xavier and Jacquinod, S. and Johnson, J. R. and Kouach, Driss and Lacombe, Gaétan and Lanza, N. and Lapauw, L. and Laserna, J. J. and Lasue, J. and Deit, L. Le and Mouëlic, Stéphane Le and Comte, Éric and Lee, Q.-M. and Legett, Carey and Léveillé, Richard and Lewin, É. and Leyrat, C. and López-Reyes, G. and Lorenz, R. D. and Lucero, Briana and Madariaga, Juan Manuel and Madsen, S.N. and Madsen, M. B. and Mangold, N. and Manni, Florent and Mariscal, Jean-François and Martínez‐Frías, Jesús and Mathieu, Karine and Mathon, Romain",
    title = "The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description",
    year = "2021",
    journal = "Space Science Reviews",
    abstract = "Abstract On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2–7 m, while providing data at sub-mm to mm scales. We report on SuperCam’s science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.",
    url = "https://doi.org/10.1007/s11214-021-00807-w",
    doi = "10.1007/s11214-021-00807-w",
    openalex = "W3153678752",
    references = "doi101016jicarus201405038, doi101080014904512011619636, doi101146annurevearth060313055024"
}

Abstract China’s first Mars exploration mission (HuoXing-1) has been named as ‘Tianwen-1’ meaning Heaven Inquiry. Tianwen-1 was launched on July 23, 2020. In this paper, the scientific objectives of earlier and current Mars exploration missions worldwide are reviewed, and the scientific objectives, payloads and preliminary scientific investigation plan of China’s first Mars exploration mission are introduced, and expected scientific achievements are analyzed.

@article{doi101007s11214021008329,
    author = "Li, Chunlai and Zhang, Rongqiao and Yu, Deng-Yun and Dong, Guangliang and Liu, Jianjun and Geng, Yan and Sun, Zezhou and Yan, Wei and Ren, Xin and Su, Yan and Zuo, Wei and Zhang, Tielong and Cao, Jinbin and Fang, Guangyou and Yang, Jianfeng and Shu, Rong and Lin, Yangting and Zou, Yongliao and Liu, Dawei and Liu, Bin and Kong, Deqing and Zhu, Xinying and Ouyang, Ziyuan",
    title = "China’s Mars Exploration Mission and Science Investigation",
    year = "2021",
    journal = "Space Science Reviews",
    abstract = "Abstract China’s first Mars exploration mission (HuoXing-1) has been named as ‘Tianwen-1’ meaning Heaven Inquiry. Tianwen-1 was launched on July 23, 2020. In this paper, the scientific objectives of earlier and current Mars exploration missions worldwide are reviewed, and the scientific objectives, payloads and preliminary scientific investigation plan of China’s first Mars exploration mission are introduced, and expected scientific achievements are analyzed.",
    url = "https://doi.org/10.1007/s11214-021-00832-9",
    doi = "10.1007/s11214-021-00832-9",
    openalex = "W3165775674",
    references = "doi101126scienceaar7268"
}

-wave shadow zone at teleseismic distances. By combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. This enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow.

@article{doi101126scienceabf2966,
    author = "Khan, Amir and Ceylan, Savas and van Driel, Martin and Giardini, Domenico and Lognonné, Philippe and Samuel, Henri and Schmerr, N. C. and Stähler, Simon C. and Durán, Cecilia and Huang, Quancheng and Kim, Doyeon and Broquet, Adrien and Charalambous, Constantinos and Clinton, John and Davis, Paul M. and Drilleau, M. and Karakostas, Foivos and Lekić, V. and McLennan, S. M. and Maguire, Ross and Michaut, Chloé and Panning, M. P. and Pike, W. T. and Pinot, Baptiste and Plasman, Matthieu and Scholz, John‐Robert and Widmer‐Schnidrig, Rudolf and Spohn, Tilman and Smrekar, S. E. and Banerdt, W. B.",
    title = "Upper mantle structure of Mars from InSight seismic data",
    year = "2021",
    journal = "Science",
    abstract = "-wave shadow zone at teleseismic distances. By combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. This enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow.",
    url = "https://doi.org/10.1126/science.abf2966",
    doi = "10.1126/science.abf2966",
    openalex = "W3183495692",
    references = "doi101038s415610200544y"
}

Observations from orbital spacecraft have shown that Jezero crater on Mars contains a prominent fan-shaped body of sedimentary rock deposited at its western margin. The Perseverance rover landed in Jezero crater in February 2021. We analyze images taken by the rover in the 3 months after landing. The fan has outcrop faces, which were invisible from orbit, that record the hydrological evolution of Jezero crater. We interpret the presence of inclined strata in these outcrops as evidence of deltas that advanced into a lake. In contrast, the uppermost fan strata are composed of boulder conglomerates, which imply deposition by episodic high-energy floods. This sedimentary succession indicates a transition from sustained hydrologic activity in a persistent lake environment to highly energetic short-duration fluvial flows.

@article{doi101126scienceabl4051,
    author = "Mangold, N. and Gupta, Sanjeev and Gasnault, O. and Dromart, Gilles and Tarnas, Jesse and Sholes, Steven and Horgan, B. and Quantin-Nataf, C. and Brown, A. J. and Mouëlic, Stéphane Le and Yingst, R. A. and Bell, J. F. and Beyssac, Olivier and Bosak, Tanja and Calef, F. J. and Ehlmann, B. L. and Farley, Kenneth A. and Grotzinger, J. P. and Hickman‐Lewis, Keyron and Holm‐Alwmark, Sanna and Kah, Linda C. and Martínez‐Frías, Jesús and McLennan, S. M. and Maurice, S. and Núñez, Jorge I. and Ollila, A. and Pilleri, P. and Rice, J. W. and Rice, M. S. and Simon, J. I. and Shuster, David L. and Stack, K. M. and Sun, V. Z. and Treiman, A. H. and Weiss, B. P. and Wiens, R. C. and Williams, Amy J. and Williams, N. R. and Williford, Kenneth H.",
    title = "Perseverance rover reveals an ancient delta-lake system and flood deposits at Jezero crater, Mars",
    year = "2021",
    journal = "Science",
    abstract = "Observations from orbital spacecraft have shown that Jezero crater on Mars contains a prominent fan-shaped body of sedimentary rock deposited at its western margin. The Perseverance rover landed in Jezero crater in February 2021. We analyze images taken by the rover in the 3 months after landing. The fan has outcrop faces, which were invisible from orbit, that record the hydrological evolution of Jezero crater. We interpret the presence of inclined strata in these outcrops as evidence of deltas that advanced into a lake. In contrast, the uppermost fan strata are composed of boulder conglomerates, which imply deposition by episodic high-energy floods. This sedimentary succession indicates a transition from sustained hydrologic activity in a persistent lake environment to highly energetic short-duration fluvial flows.",
    url = "https://doi.org/10.1126/science.abl4051",
    doi = "10.1126/science.abl4051",
    openalex = "W3202970776",
    references = "doi1010292007je003000"
}

. However, 45 years have passed since Viking-2 provided ground-based detection results. Here we report an in situ ground-penetrating radar survey of Martian subsurface structure in a southern marginal area of Utopia Planitia conducted by the Zhurong rover of the Tianwen-1 mission. A detailed subsurface image profile is constructed along the roughly 1,171 m traverse of the rover, showing an approximately 70-m-thick, multi-layered structure below a less than 10-m-thick regolith. Although alternative models deserve further scrutiny, the new radar image suggests the occurrence of episodic hydraulic flooding sedimentation that is interpreted to represent the basin infilling of Utopia Planitia during the Late Hesperian to Amazonian. While no direct evidence for the existence of liquid water was found within the radar detection depth range, we cannot rule out the presence of saline ice in the subsurface of the landing area.

@article{doi101038s41586022051475,
    author = "Li, Chao and Zheng, Yikang and Wang, Xin and Zhang, Jinhai and Wang, Yibo and Chen, Ling and Zhang, Lei and Zhao, Pan and Liu, Yike and Lv, Wenmin and Liu, Yang and Zhao, Xu and Hao, Jinlai and Sun, Weijia and Liu, Xiaofeng and Jia, Bojun and Li, Juan and Lan, Haiqiang and Fa, Wenzhe and Pan, Yongxin and Wu, Fu‐Yuan",
    title = "Layered subsurface in Utopia Basin of Mars revealed by Zhurong rover radar",
    year = "2022",
    journal = "Nature",
    abstract = ". However, 45 years have passed since Viking-2 provided ground-based detection results. Here we report an in situ ground-penetrating radar survey of Martian subsurface structure in a southern marginal area of Utopia Planitia conducted by the Zhurong rover of the Tianwen-1 mission. A detailed subsurface image profile is constructed along the roughly 1,171 m traverse of the rover, showing an approximately 70-m-thick, multi-layered structure below a less than 10-m-thick regolith. Although alternative models deserve further scrutiny, the new radar image suggests the occurrence of episodic hydraulic flooding sedimentation that is interpreted to represent the basin infilling of Utopia Planitia during the Late Hesperian to Amazonian. While no direct evidence for the existence of liquid water was found within the radar detection depth range, we cannot rule out the presence of saline ice in the subsurface of the landing area.",
    url = "https://doi.org/10.1038/s41586-022-05147-5",
    doi = "10.1038/s41586-022-05147-5",
    openalex = "W4297242811",
    references = "doi101126scienceaar7268"
}