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Methane on Mars and Habitability: Challenges and Responses

Yung, Yuk L. and Chen, Pin and Nealson, Kenneth and Atreya, Sushil and Beckett, Patrick and Blank, Jennifer and Ehlmann, Bethany and Eiler, John and Etiope, Giuseppe and Ferry, James G. and Forget, Francois and Gao, Peter and Hu, Renyu and Kleinböhl, Armin and Klusman, Ronald and Lefèvre, Franck and Miller, Charles and Mischna, Michael and Mumma, Michael and Newman, Sally and Oehler, Dorothy and Okumura, Mitchio and Oremland, Ronald and Orphan, Victoria and Popa, Radu and Russell, Michael and Shen, Linhan and Sherwood Lollar, Barbara and Stamenković, Vlada and Staehle, Robert and Stolper, Daniel and Templeton, Alexis and Vandaele, Ann C. and Viscardy, Sébastien and Webster, Chris and Wennberg, Paul O. and Wong, Michael and Worden, John (2018) Methane on Mars and Habitability: Challenges and Responses. , Pasadena, CA. https://resolver.caltech.edu/CaltechAUTHORS:20180426-110252898

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Abstract

Recent measurements of methane (CH_4) by the Mars Science Laboratory (MSL) now confront us with robust data that demand interpretation. Thus far, the MSL data have revealed a baseline level of CH_4 (∼0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH_4 with peak abundances of ∼7 ppbv. What do these CH_4 revelations with drastically different abundances and temporal signatures represent in terms of interior geochemical processes, or is martian CH_4 a biosignature? Discerning how CH_4 generation occurs on Mars may shed light on the potential habitability of Mars. There is no evidence of life on the surface of Mars today, but microbes might reside beneath the surface. In this case, the carbon flux represented by CH_4 would serve as a link between a putative subterranean biosphere on Mars and what we can measure above the surface. Alternatively, CH_4 records modern geochemical activity. Here we ask the fundamental question: how active is Mars, geochemically and/or biologically? In this article, we examine geological, geochemical, and biogeochemical processes related to our overarching question. The martian atmosphere and surface are an overwhelmingly oxidizing environment, and life requires pairing of electron donors and electron acceptors, that is, redox gradients, as an essential source of energy. Therefore, a fundamental and critical question regarding the possibility of life on Mars is, “Where can we find redox gradients as energy sources for life on Mars?” Hence, regardless of the pathway that generates CH_4 on Mars, the presence of CH_4, a reduced species in an oxidant-rich environment, suggests the possibility of redox gradients supporting life and habitability on Mars. Recent missions such as ExoMars Trace Gas Orbiter may provide mapping of the global distribution of CH_4. To discriminate between abiotic and biotic sources of CH_4 on Mars, future studies should use a series of diagnostic geochemical analyses, preferably performed below the ground or at the ground/atmosphere interface, including measurements of CH_4 isotopes, methane/ethane ratios, H_2 gas concentration, and species such as acetic acid. Advances in the fields of Mars exploration and instrumentation will be driven, augmented, and supported by an improved understanding of atmospheric chemistry and dynamics, deep subsurface biogeochemistry, astrobiology, planetary geology, and geophysics. Future Mars exploration programs will have to expand the integration of complementary areas of expertise to generate synergistic and innovative ideas to realize breakthroughs in advancing our understanding of the potential of life and habitable conditions having existed on Mars. In this spirit, we conducted a set of interdisciplinary workshops. From this series has emerged a vision of technological, theoretical, and methodological innovations to explore the martian subsurface and to enhance spatial tracking of key volatiles, such as CH_4.


Item Type:Report or Paper (Technical Report)
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http://resolver.caltech.edu/CaltechAUTHORS:20180925-073151228Related ItemArticle
ORCID:
AuthorORCID
Yung, Yuk L.0000-0002-4263-2562
Nealson, Kenneth0000-0001-5189-3732
Atreya, Sushil0000-0002-1972-1815
Ehlmann, Bethany0000-0002-2745-3240
Gao, Peter0000-0002-8518-9601
Hu, Renyu0000-0003-2215-8485
Miller, Charles0000-0002-9380-4838
Mischna, Michael0000-0002-8022-5319
Newman, Sally0000-0003-0710-995X
Okumura, Mitchio0000-0001-6874-1137
Orphan, Victoria0000-0002-5374-6178
Shen, Linhan0000-0003-3871-655X
Stamenković, Vlada0000-0003-2416-3683
Stolper, Daniel0000-0003-3299-3177
Wennberg, Paul O.0000-0002-6126-3854
Additional Information:Study Report prepared for the Keck Institute for Space Studies (KISS). We dedicate this report to JPL scientist Mark Allen, whose spirit of generosity inspired many of the conversations and much of the work that brought us together. We thank the Director of the Keck Institute for Space Studies, Tom Prince, the Executive Director, Michele Judd, and the fantastic KISS staff for hosting our workshop and providing a wonderful environment for these discussions.
Group:Keck Institute for Space Studies
DOI:10.7907/Z990220K
Record Number:CaltechAUTHORS:20180426-110252898
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180426-110252898
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86060
Collection:CaltechAUTHORS
Deposited By: Iryna Chatila
Deposited On:26 Apr 2018 20:22
Last Modified:28 Oct 2019 23:26

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