PMID- 30234380 OWN - NLM STAT- MEDLINE DCOM- 20190927 LR - 20231004 IS - 1557-8070 (Electronic) IS - 1531-1074 (Print) IS - 1557-8070 (Linking) VI - 18 IP - 10 DP - 2018 Oct TI - Methane on Mars and Habitability: Challenges and Responses. PG - 1221-1242 LID - 10.1089/ast.2018.1917 [doi] AB - 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) ( approximately 0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH(4) with peak abundances of approximately 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). FAU - Yung, Yuk L AU - Yung YL AD - 1 California Institute of Technology , Pasadena, California. AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Chen, Pin AU - Chen P AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Nealson, Kenneth AU - Nealson K AD - 3 University of Southern California , Los Angeles, California. FAU - Atreya, Sushil AU - Atreya S AD - 4 University of Michigan , Ann Arbor, Michigan. FAU - Beckett, Patrick AU - Beckett P AD - 5 University of California , Davis, California. FAU - Blank, Jennifer G AU - Blank JG AD - 6 NASA Ames Research Center , Blue Marble Space Institute of Science, Mountain View, California. FAU - Ehlmann, Bethany AU - Ehlmann B AD - 1 California Institute of Technology , Pasadena, California. AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Eiler, John AU - Eiler J AD - 1 California Institute of Technology , Pasadena, California. FAU - Etiope, Giuseppe AU - Etiope G AD - 7 Istituto Nazionale di Geofisica e Vulcanologia , Rome, Italy . AD - 8 Faculty of Environmental Science and Engineering, Babes-Bolyai University , Cluj-Napoca, Romania . FAU - Ferry, James G AU - Ferry JG AD - 9 The Pennsylvania State University, University Park , Pennsylvania. FAU - Forget, Francois AU - Forget F AD - 10 Laboratoire de Meteorologie Dynamique, Institut Pierre Simon Laplace , CNRS, Paris, France . FAU - Gao, Peter AU - Gao P AD - 11 University of California , Berkeley, California. FAU - Hu, Renyu AU - Hu R AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Kleinbohl, Armin AU - Kleinbohl A AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Klusman, Ronald AU - Klusman R AD - 12 Colorado School of Mines , Golden, Colorado. FAU - Lefevre, Franck AU - Lefevre F AD - 13 Laboratoire Atmospheres, Milieux, Observations Spatiales (LATMOS) , IPSL, Paris, France . FAU - Miller, Charles AU - Miller C AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Mischna, Michael AU - Mischna M AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Mumma, Michael AU - Mumma M AD - 14 NASA Goddard Space Flight Center , Greenbelt, Maryland. FAU - Newman, Sally AU - Newman S AD - 1 California Institute of Technology , Pasadena, California. FAU - Oehler, Dorothy AU - Oehler D AD - 15 Planetary Science Institute , Tucson, Arizona. FAU - Okumura, Mitchio AU - Okumura M AD - 1 California Institute of Technology , Pasadena, California. FAU - Oremland, Ronald AU - Oremland R AD - 16 US Geological Survey , Menlo Park, California. FAU - Orphan, Victoria AU - Orphan V AD - 1 California Institute of Technology , Pasadena, California. FAU - Popa, Radu AU - Popa R AD - 3 University of Southern California , Los Angeles, California. FAU - Russell, Michael AU - Russell M AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Shen, Linhan AU - Shen L AD - 1 California Institute of Technology , Pasadena, California. FAU - Sherwood Lollar, Barbara AU - Sherwood Lollar B AD - 17 University of Toronto , Toronto Ontario, Canada . FAU - Staehle, Robert AU - Staehle R AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Stamenkovic, Vlada AU - Stamenkovic V AD - 1 California Institute of Technology , Pasadena, California. AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Stolper, Daniel AU - Stolper D AD - 11 University of California , Berkeley, California. FAU - Templeton, Alexis AU - Templeton A AD - 18 University of Colorado , Boulder, Colorado. FAU - Vandaele, Ann C AU - Vandaele AC AD - 19 The Royal Belgian Institute for Space Aeronomy (BIRA-IASB) , Brussels, Belgium . FAU - Viscardy, Sebastien AU - Viscardy S AD - 19 The Royal Belgian Institute for Space Aeronomy (BIRA-IASB) , Brussels, Belgium . FAU - Webster, Christopher R AU - Webster CR AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. FAU - Wennberg, Paul O AU - Wennberg PO AD - 1 California Institute of Technology , Pasadena, California. FAU - Wong, Michael L AU - Wong ML AD - 1 California Institute of Technology , Pasadena, California. FAU - Worden, John AU - Worden J AD - 2 NASA Jet Propulsion Laboratory, California Institute of Technology , Pasadena, California. LA - eng PT - Journal Article PT - Research Support, Non-U.S. Gov't PT - Research Support, U.S. Gov't, Non-P.H.S. PT - Review DEP - 20180919 PL - United States TA - Astrobiology JT - Astrobiology JID - 101088083 RN - OP0UW79H66 (Methane) SB - IM MH - *Exobiology MH - *Extraterrestrial Environment MH - *Mars MH - Methane/*analysis MH - Spectrum Analysis MH - Time Factors PMC - PMC6205098 OTO - NOTNLM OT - CH4 OT - Mars OT - Mars instrumentation OT - Subsurface redox conditions COIS- No competing financial interests exist. EDAT- 2018/09/21 06:00 MHDA- 2019/09/29 06:00 PMCR- 2018/10/12 CRDT- 2018/09/21 06:00 PHST- 2018/09/21 06:00 [pubmed] PHST- 2019/09/29 06:00 [medline] PHST- 2018/09/21 06:00 [entrez] PHST- 2018/10/12 00:00 [pmc-release] AID - 10.1089/ast.2018.1917 [pii] AID - 10.1089/ast.2018.1917 [doi] PST - ppublish SO - Astrobiology. 2018 Oct;18(10):1221-1242. doi: 10.1089/ast.2018.1917. Epub 2018 Sep 19.