Methane on Mars and Habitability: Challenges and Responses

被引:66
作者
Yung, Yuk L. [1 ,2 ]
Chen, Pin [2 ]
Nealson, Kenneth [3 ]
Atreya, Sushil [4 ]
Beckett, Patrick [5 ]
Blank, Jennifer G. [6 ]
Ehlmann, Bethany [1 ,2 ]
Eiler, John [1 ]
Etiope, Giuseppe [7 ,8 ]
Ferry, James G. [9 ]
Forget, Francois [10 ]
Gao, Peter [11 ]
Hu, Renyu [2 ]
Kleinbohl, Armin [2 ]
Klusman, Ronald [12 ]
Lefevre, Franck [13 ]
Miller, Charles [2 ]
Mischna, Michael [2 ]
Mumma, Michael [14 ]
Newman, Sally [1 ]
Oehler, Dorothy [15 ]
Okumura, Mitchio [1 ]
Oremland, Ronald [16 ]
Orphan, Victoria [1 ]
Popa, Radu [3 ]
Russell, Michael [2 ]
Shen, Linhan [1 ]
Lollar, Barbara Sherwood [17 ]
Staehle, Robert [2 ]
Stamenkovic, Vlada [1 ,2 ]
Templeton, Alexis [18 ]
Vandaele, Ann C. [19 ]
Viscardy, Sebastien [19 ]
Webster, Christopher R. [2 ]
Wennberg, Paul O. [1 ]
Wong, Michael L. [1 ]
Worden, John [2 ]
机构
[1] CALTECH, Pasadena, CA 91125 USA
[2] CALTECH, Jet Prop Lab, NASA, Pasadena, CA USA
[3] Univ Southern Calif, Los Angeles, CA USA
[4] Univ Michigan, Ann Arbor, MI 48109 USA
[5] Univ Calif Davis, Davis, CA 95616 USA
[6] NASA, Ames Res Ctr, Blue Marble Space Inst Sci, Mountain View, CA USA
[7] Ist Nazl Geofis & Vulcanol, Rome, Italy
[8] Babes Bolyai Univ, Fac Environm Sci & Engn, Cluj Napoca, Romania
[9] Penn State Univ, University Pk, PA 16802 USA
[10] CNRS, Inst Pierre Simon Laplace, Lab Meteorol Dynam, Paris, France
[11] Univ Calif Berkeley, Berkeley, CA USA
[12] Colorado Sch Mines, Golden, CO 80401 USA
[13] IPSL, Lab Atmospheres, Observat Spatiales LATMOS, Milieux, Paris, France
[14] NASA, Goddard Space Flight Ctr, Greenbelt, MD USA
[15] Planetary Sci Inst, Tucson, AZ USA
[16] US Geol Survey, 345 Middlefield Rd, Menlo Pk, CA 94025 USA
[17] Univ Toronto, Toronto, ON, Canada
[18] Univ Colorado, Boulder, CO 80309 USA
[19] Royal Belgian Inst Space Aeron BIRA IASB, Brussels, Belgium
关键词
Mars; CH4; Subsurface redox conditions; Mars instrumentation; Astrobiology; 18; xxx-xxx; DETACHED DUST LAYERS; MARTIAN ATMOSPHERE; GALE CRATER; MIDDLE ATMOSPHERE; SUBSURFACE WATER; COMETARY ORIGIN; CLAY-MINERALS; NEAR-SURFACE; HIGH-ENERGY; LIFE;
D O I
10.1089/ast.2018.1917
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Recent measurements of methane (CH4) 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 CH4 (approximate to 0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH4 with peak abundances of approximate to 7ppbv. What do these CH4 revelations with drastically different abundances and temporal signatures represent in terms of interior geochemical processes, or is martian CH4 a biosignature? Discerning how CH4 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 CH4 would serve as a link between a putative subterranean biosphere on Mars and what we can measure above the surface. Alternatively, CH4 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 CH4 on Mars, the presence of CH4, 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 CH4. To discriminate between abiotic and biotic sources of CH4 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 CH4 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 CH4.
引用
收藏
页码:1221 / 1242
页数:22
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