Laurie A. Leshin

Abundance and isotopic composition of gases in the Martian atmosphere from the Curiosity rover

Mars Atmosphere from Curiosity The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. Mahaffy et al. (p. 263) present volume-mixing ratios of Mars five major atmospheric constituents (CO2, Ar, N2, O2, and CO) and isotope measurements of 40Ar/36Ar and C and O in CO2, based on data from one of SAMs instruments, obtained between 31 August and 21 November 2012. Webster et al. (p. 260) used data from another of SAMs instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO2 and H2O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO2 and H2O were largely established after the period of early atmospheric loss some 4 billion years ago. Data from the Curiosity rover provide a detailed account of the chemical and isotopic composition of Mars’ atmosphere. Volume mixing and isotope ratios secured with repeated atmospheric measurements taken with the Sample Analysis at Mars instrument suite on the Curiosity rover are: carbon dioxide (CO2), 0.960(±0.007); argon-40 (40Ar), 0.0193(±0.0001); nitrogen (N2), 0.0189(±0.0003); oxygen, 1.45(±0.09) × 10−3; carbon monoxide, < 1.0 × 10−3; and 40Ar/36Ar, 1.9(±0.3) × 103. The 40Ar/N2 ratio is 1.7 times greater and the 40Ar/36Ar ratio 1.6 times lower than values reported by the Viking Lander mass spectrometer in 1976, whereas other values are generally consistent with Viking and remote sensing observations. The 40Ar/36Ar ratio is consistent with martian meteoritic values, which provides additional strong support for a martian origin of these rocks. The isotopic signature δ13C from CO2 of ~45 per mil is independently measured with two instruments. This heavy isotope enrichment in carbon supports the hypothesis of substantial atmospheric loss.

Isotope Ratios of H, C, and O in CO2 and H2O of the Martian Atmosphere

Mars Atmosphere from Curiosity The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. Mahaffy et al. (p. 263) present volume-mixing ratios of Mars five major atmospheric constituents (CO2, Ar, N2, O2, and CO) and isotope measurements of 40Ar/36Ar and C and O in CO2, based on data from one of SAMs instruments, obtained between 31 August and 21 November 2012. Webster et al. (p. 260) used data from another of SAMs instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO2 and H2O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO2 and H2O were largely established after the period of early atmospheric loss some 4 billion years ago. Data from the Curiosity rover provide a detailed account of the chemical and isotopic composition of Mars’ atmosphere. Stable isotope ratios of H, C, and O are powerful indicators of a wide variety of planetary geophysical processes, and for Mars they reveal the record of loss of its atmosphere and subsequent interactions with its surface such as carbonate formation. We report in situ measurements of the isotopic ratios of D/H and 18O/16O in water and 13C/12C, 18O/16O, 17O/16O, and 13C18O/12C16O in carbon dioxide, made in the martian atmosphere at Gale Crater from the Curiosity rover using the Sample Analysis at Mars (SAM)’s tunable laser spectrometer (TLS). Comparison between our measurements in the modern atmosphere and those of martian meteorites such as ALH 84001 implies that the martian reservoirs of CO2 and H2O were largely established ~4 billion years ago, but that atmospheric loss or surface interaction may be still ongoing.

Abundances and implications of volatile‐bearing species from evolved gas analysis of the Rocknest aeolian deposit, Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) rover Curiosity detected evolved gases during thermal analysis of soil samples from the Rocknest aeolian deposit in Gale Crater. Major species detected (in order of decreasing molar abundance) were H2O, SO2, CO2, and O2, all at the µmol level, with HCl, H2S, NH3, NO, and HCN present at the tens to hundreds of nmol level. We compute weight % numbers for the major gases evolved by assuming a likely source and calculate abundances between 0.5 and 3 wt.%. The evolution of these gases implies the presence of both oxidized (perchlorates) and reduced (sulfides or H-bearing) species as well as minerals formed under alkaline (carbonates) and possibly acidic (sulfates) conditions. Possible source phases in the Rocknest material are hydrated amorphous material, minor clay minerals, and hydrated perchlorate salts (all potential H2O sources), carbonates (CO2), perchlorates (O2 and HCl), and potential N-bearing materials (e.g., Martian nitrates, terrestrial or Martian nitrogenated organics, ammonium salts) that evolve NH3, NO, and/or HCN. We conclude that Rocknest materials are a physical mixture in chemical disequilibrium, consistent with aeolian mixing, and that although weathering is not extensive, it may be ongoing even under current Martian surface conditions.

Chemistry of fracture‐filling raised ridges in Yellowknife Bay, Gale Crater: Window into past aqueous activity and habitability on Mars

The ChemCam instrument package on the Curiosity rover was used to characterize distinctive raised ridges in the Sheepbed mudstone, Yellowknife Bay formation, Gale Crater. The multilayered, fracture-filling ridges are more resistant to erosion than the Sheepbed mudstone rock in which they occur. The bulk average composition of the raised ridges is enriched in MgO by 1.2-1.7 times (average of 8.3-11.4 wt %; single-shot maximum of 17.0 wt %) over that of the mudstone. Al2O3 is anticorrelated with MgO, while Li is somewhat enriched where MgO is highest. Some ridges show a variation in composition with different layers on a submillimeter scale. In particular, the McGrath target shows similar high-MgO resistant outer layers and a low-MgO, less resistant inner layer. This is consistent with the interpretation that the raised ridges are isopachous fracture-filling cements with a stratigraphy that likely reveals changes in fluid composition or depositional conditions over time. Overall, the average composition of the raised ridges is close to that of a Mg- and Fe-rich smectite, or saponite, which may also be the main clay mineral constituent of the host mudstone. These analyses provide evidence of diagenesis and aqueous activity in the early postdepositional history of the Yellowknife Bay formation, consistent with a low salinity to brackish fluid at near-neutral or slightly alkaline pH. The fluids that circulated through the fractures likely interacted with the Sheepbed mudstone and (or) other stratigraphically adjacent rock units of basaltic composition and leached Mg from them preferentially.

Primordial argon isotope fractionation in the atmosphere of Mars measured by the SAM instrument on Curiosity and implications for atmospheric loss.

[1] The quadrupole mass spectrometer of the Sample Analysis at Mars (SAM) instrument on Curiosity rover has made the first high-precision measurement of the nonradiogenic argon isotope ratio in the atmosphere of Mars. The resulting value of 36Ar/38Aru2009=u20094.2u2009±u20090.1 is highly significant for it provides excellent evidence that “Mars” meteorites are indeed of Martian origin, and it points to a significant loss of argon of at least 50% and perhaps as high as 85–95% from the atmosphere of Mars in the past 4 billion years. Taken together with the isotopic fractionations in N, C, H, and O measured by SAM, these results imply a substantial loss of atmosphere from Mars in the posthydrodynamic escape phase.

Squyres Receives 2012 Whipple Award: Citation

Steven Squyres received the 2012 Whipple Award at the 2012 AGU Fall Meeting, held 3–7 December in San Francisco, Calif. The award recognizes an individual who has made an outstanding contribution in the field of planetary science.

Hayes Receives 2012 Ronald Greeley Early Career Award in Planetary Science: Citation

Alexander G. Hayes Jr. received the 2012 Ronald Greeley Early Career Award in Planetary Science at the 2012 AGU Fall Meeting, held 3–7 December in San Francisco, Calif. The award recognizes significant early-career contributions to planetary science.

Veverka receives 2011 Whipple Award: Citation

Joseph Veverka received the 2011 Whipple Award at the 2011 AGU Fall Meeting, held 5–9 December in San Francisco, Calif. The award recognizes an individual who has made an outstanding contribution in the field of planetary science.