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We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale Crater. A K-Ar age of 4.21 ± 0.35 billion years represents a mixture of detrital and authigenic components and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced ³He, 21Ne, and 36Ar yield concordant surface exposure ages of 78 ± 30 million years. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation. [ABSTRACT FROM AUTHOR]

Cl isotope ratios measured on HCl thermally evolved from as-yet-unknown phases in sedimentary rocks and sand in Gale Crater provide unexpected insights to the Martian surficial Cl cycle. The seven samples yield δ 37 Cl values ranging from − 1 ± 25 ‰ to − 51 ± 5 ‰ . Five analyses from two samples of the Sheepbed mudstone (Yellowknife Bay study area) are analytically indistinguishable with a mean δ 37 Cl of − 11 ± 7 ‰ ( 1 σ ) . In contrast, four mudstones/sandstones from the Kimberley and Pahrump study areas also yielded indistinguishable ratios, but with a mean δ 37 Cl of − 43 ± 6 ‰ . The Rocknest sand deposit gave a highly uncertain δ 37 Cl value of − 7 ± 44 ‰ . These light and highly variable δ 37 Cl values are unique among known solar system materials. Two endmember models are offered to account for these observations, and in both, perchlorate, with its extreme ability to fractionate Cl isotopes, is critical. In the first model, SAM is detecting HCl from an oxychlorine compound (e.g., perchlorate) produced from volcanic gas emissions by atmospheric chemical reactions. Similar reactions in Earth's atmosphere may be responsible for the isotopically lightest known Cl outside of this study, in perchlorate from the Atacama Desert. Some of the Gale Crater δ 37 Cl values are more negative than those in Atacama perchlorate, but because reaction mechanisms and associated fractionation factors are unknown, it is impossible to assess whether this difference is prohibitive. If the negative δ 37 Cl signal is produced in this fashion, the isotopic variability among samples could arise either from variations in the relative size of the reactant chloride and product perchlorate reservoirs, or from variations in the fraction of perchlorate reduced back to chloride after deposition. Such reduction strongly enriches 37 Cl in the residual perchlorate. Perchlorate reduction alone offers an alternative endmember model that can explain the observed data if SAM measured HCl derived from chloride. In this model isotopically normal perchlorate produced by an unspecified mechanism is reduced to chloride. Depending on the relative size of the reduced reservoir, the integrated product chloride can vary in isotopic composition from − 70 ‰ in the first increment all the way to the starting composition if the perchlorate is fully reduced. Thus, variable degrees of perchlorate reduction can produce chloride with the appropriate δ 37 Cl range. Combination of the two endmember models, in which the perchlorate subject to post-deposition reduction is isotopically negative from atmospheric reactions, is also possible. Determination of the phase hosting the Cl measured by SAM, an oxychlorine compound or chloride, is critical for selecting between these models, and for developing implications of the results for the Mars surficial Cl cycle. At present it is not possible to conclusively establish which phase is responsible (possibly both), but limited evidence favors the conclusion that the measured Cl derives mostly from an oxychlorine compound. [ABSTRACT FROM AUTHOR]

Abstract: We present the Volatile Analysis by Pyrolysis of Regolith (VAPoR) instrument design and demonstrate the validity of an in situ pyrolysis mass spectrometer for evolved gas analyses of lunar and planetary regolith samples. In situ evolved gas analyses of the lunar regolith have not yet been carried out and no atmospheric or evolved gas measurements have been made at the lunar poles. VAPoR is designed to do both kinds of measurements, is currently under development at NASA’s Goddard Space Flight Center, and will be able to heat powdered regolith samples or rock drill fines up to 1400°C in vacuo. To validate the instrument concept, evolved gas species released from different planetary analogs were determined as a function of temperature using a laboratory breadboard. Evolved gas measurements of an Apollo 16 regolith sample and a fragment of the carbonaceous meteorite Murchison were made by VAPoR and our results compared with existing data. The results imply that in situ evolved gas measurements of the lunar regolith at the polar regions by VAPoR will be a very powerful tool for identifying water and other volatile signatures of lunar or exogenous origin as potential resources for future human exploration. [Copyright &y& Elsevier]

The deuterium-to-hydrogen (D/H) ratio in strongly bound water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of these minerals. Curiosity's Sample Analysis at Mars (SAM) experiment measured thermally evolved water and hydrogen gas released between 550° and 950°C from samples of Hesperian-era Gale crater smectite to determine this isotope ratio. The D/H value is 3.0 (®0.2) times the ratio in standard mean ocean water. The D/H ratio in this ~3-billion-year-old mudstone, which is half that of the present martian atmosphere but substantially higher than that expected in very early Mars, indicates an extended history of hydrogen escape and desiccation of the planet. [ABSTRACT FROM AUTHOR]