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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 G. and Ehlmann, Bethany and Eiler, John and Etiope, Giuseppe and Ferry, James G. and Forget, François 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 Staehle, Robert and Stamenković, Vlada and Stolper, Daniel and Templeton, Alexis and Vandaele, Ann C. and Viscardy, Sébastien and Webster, Christopher R. and Wennberg, Paul O. and Wong, Michael L. and Worden, John (2018) Methane on Mars and Habitability: Challenges and Responses. Astrobiology, 18 (10). pp. 1221-1242. ISSN 1557-8070. PMCID PMC6205098. doi:10.1089/ast.2018.1917.

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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:Article
Related URLs:
URLURL TypeDescription ItemReport CentralArticle
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
Worden, John0000-0003-0257-9549
Additional Information:© 2018 Yuk L. Yung et al., Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Published Online: 19 Sep 2018. We dedicate this article to JPL scientist Mark Allen, whose spirit of generosity inspired many of the conversations and much of the work that brought us together. This work was initiated and supported by the W.M. Keck Institute for Space Studies. We thank the Director of the Keck Institute for Space Studies, Tom Prince, the Executive Director, Michele Judd, and the capable and dedicated KISS staff for hosting and supporting the workshops that led to this article. We thank Charles Carter for the cover illustration and Meg Rosenberg for her work on editing and formatting. We thank Danica Adams, Siteng Fan, Amanda Gao, Mimi Gerstell, Yancheng Luo, Aimee Oz, Andrew Sappey, Sindhoora Tallapragada, and Kyle Weng for their efforts in editing the article. We thank Daniel Stolper for his participation and input in the workshop. The research was partly carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. No competing financial interests exist.
Group:Keck Institute for Space Studies, Astronomy Department
Funding AgencyGrant Number
Keck Institute for Space Studies (KISS)UNSPECIFIED
Issue or Number:10
PubMed Central ID:PMC6205098
Record Number:CaltechAUTHORS:20180925-073151228
Persistent URL:
Official Citation:Methane on Mars and Habitability: Challenges and Responses. Yuk L. Yung, Pin Chen, Kenneth Nealson, Sushil Atreya, Patrick Beckett, Jennifer G. Blank, Bethany Ehlmann, John Eiler, Giuseppe Etiope, James G. Ferry, Francois Forget, Peter Gao, Renyu Hu, Armin Kleinböhl, Ronald Klusman, Franck Lefèvre, Charles Miller, Michael Mischna, Michael Mumma, Sally Newman, Dorothy Oehler, Mitchio Okumura, Ronald Oremland, Victoria Orphan, Radu Popa, Michael Russell, Linhan Shen, Barbara Sherwood Lollar, Robert Staehle, Vlada Stamenković, Daniel Stolper, Alexis Templeton, Ann C. Vandaele, Sébastien Viscardy, Christopher R. Webster, Paul O. Wennberg, Michael L. Wong, and John Worden. Astrobiology 2018 18:10, 1221-1242
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89898
Deposited By: Tony Diaz
Deposited On:25 Sep 2018 16:34
Last Modified:16 Nov 2021 00:39

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