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 (∼0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH4 with peak abundances of ∼7 ppbv. 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, H2 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.

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

John Worden

Astrobiology

ASTROBIOLOGY 是被引用次数最多的同行评审期刊，致力于了解生命的起源、进化和宇宙中的分布，重点关注行星际探索和实验室研究的新发现和发现。ASTROBIOLOGY 覆盖范围包括：天体物理学；天体古生物学; 行星; 生物天文学; 宇宙化学; 生态基因组学; 外星生物学; 极端微生物; 地球微生物学; 引力生物学; 生命探测技术; 陨石学; 行星地球科学; 行星保护; 益生元化学; 空间探索技术; 地球化

Astrobiology is the most cited peer-reviewed journal dedicated to understanding the origin, evolution, and distribution of life in the universe. It focuses on new discoveries in planetary exploration and laboratory research. The scope of Astrobiology includes: astrophysics, astrobiology, planets, bioastronomy, astrochemistry, ecological genomics, exobiology, extremophiles, earth microbiology, gravitational biology, life detection technologies, meteoritics, planetary earth sciences, planetary protection, prebiotic chemistry, space exploration technologies, and geochemistry.

《Astrobiology》是引用次数最多的同行评审期刊，专注于生命的起源、进化及其在宇宙中的分布。期刊特别关注行星际探索和实验室研究中的新发现。其覆盖范围包括：天体物理学、天体古生物学、行星、生物天文学、宇宙化学、生态基因组学、外星生物学、极端微生物、地球微生物学、引力生物学、生命探测技术、陨石学、行星地球科学、行星保护、益生元化学、空间探索技术及地球化学。

Methane on Mars and Habitability: Challenges and Responses

Geological, geochemical, and biogeochemical processes related to the fundamental question: how active is Mars, geochemically and/or biologically, are examined, which suggests the possibility of redox gradients supporting life and habitability on Mars.

火星甲烷与宜居性：挑战与回应

Category	Quartile
物理与天体物理	3
物理与天体物理, 天文与天体物理	2
物理与天体物理, 生物学	3
物理与天体物理, 地球科学综合	3

Methane on Mars and Habitability: Challenges and Responses

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Journal Info

Category	Quartile
GEOSCIENCES, MULTIDISCIPLINARY	1