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Published July 2016 | Submitted + Published
Journal Article Open

Hypotheses for Near-Surface Exchange of Methane on Mars


The Curiosity rover recently detected a background of 0.7 ppb and spikes of 7 ppb of methane on Mars. This in situ measurement reorients our understanding of the martian environment and its potential for life, as the current theories do not entail any geological source or sink of methane that varies sub-annually. In particular, the 10-fold elevation during the southern winter indicates episodic sources of methane that are yet to be discovered. Here we suggest a near-surface reservoir could explain this variability. Using the temperature and humidity measurements from the rover, we find that perchlorate salts in the regolith deliquesce to form liquid solutions, and deliquescence progresses to deeper subsurface in the season of the methane spikes. We therefore formulate the following three testable hypotheses. The first scenario is that the regolith in Gale Crater adsorbs methane when dry and releases this methane to the atmosphere upon deliquescence. The adsorption energy needs to be 36 kJ mol^(−1) to explain the magnitude of the methane spikes, higher than existing laboratory measurements. The second scenario is that microorganisms convert organic matter in the soil to methane when they are in liquid solutions. This scenario does not require regolith adsorption but entails extant life on Mars. The third scenario is that deep subsurface aquifers produce the bursts of methane. Continued in situ measurements of methane and water, as well as laboratory studies of adsorption and deliquescence, will test these hypotheses and inform the existence of the near-surface reservoir and its exchange with the atmosphere.

Additional Information

© 2016 Mary Ann Liebert, Inc. publishers. Submitted 16 September 2015; Accepted 8 April 2016; Online Ahead of Print: June 17, 2016. Support was partially provided by the National Aeronautics and Space Administration (NASA) through Hubble Fellowship grant #51332.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Y.L.Y. was supported in part by a NAI Virtual Planetary Laboratory grant from the University of Washington to the Jet Propulsion Laboratory (JPL) and California Institute of Technology. The research was carried out at the JPL, California Institute of Technology, under a contract with NASA.

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Published - ast.2015hu,renyu.pdf

Submitted - 1604.08279v1.pdf


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