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Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life

Schwieterman, Edward W. and Kiang, Nancy Y. and Parenteau, Mary N. and Harman, Chester E. and DasSarma, Shiladitya and Fisher, Theresa M. and Arney, Giada N. and Hartnett, Hilairy E. and Reinhard, Christopher T. and Olson, Stephanie L. and Meadows, Victoria S. and Cockell, Charles S. and Walker, Sara I. and Grenfell, John Lee and Hegde, Siddharth and Rugheimer, Sarah and Hu, Renyu and Lyons, Timothy W. (2018) Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life. Astrobiology, 18 (6). pp. 663-708. ISSN 1531-1074. doi:10.1089/ast.2017.1729.

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In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward.

Item Type:Article
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URLURL TypeDescription
Harman, Chester E.0000-0003-2281-1990
Reinhard, Christopher T.0000-0002-2632-1027
Rugheimer, Sarah0000-0003-1620-7658
Hu, Renyu0000-0003-2215-8485
Additional Information:© Edward W. Schwieterman et al., 2018; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License ( which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited. Received 27 July 2017; Accepted 10 December 2017; Published online 4 May 2018. The authors thank the NASA Astrobiology Program and the Nexus for Exoplanet System Science (NExSS) for their support of the NExSS Exoplanet Biosignatures Workshop. Conversations at this workshop, held in the summer of 2016 in Seattle, formed the basis for the drafting of the five review articles in this issue. They also thank Mary Voytek, the senior scientist of NASA Astrobiology, for her leadership of NExSS and her feedback on our organization of the workshop and article. E.W.S. is additionally grateful for support from the NASA Postdoctoral Program, administered by the Universities Space Research Association. This work was also supported by the NASA Astrobiology Institute, including the VPL under Cooperative Agreement Number NNA13AA93A and the Alternative Earths team under Cooperative Agreement Number NNA15BB03A. S.D. acknowledges support from NASA exobiology grant NNX15AM07G. The research of R.H. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The authors thank the following individuals for helpful comments, suggestions, and discussion during the community review period: Tanai Cardona, Anthony Del Genio, Stephen Kane, and Enric Pallé. Finally, the authors are thankful for the helpful comments from two anonymous referees, which allowed us to further improve the paper. No competing financial interests exist.
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:Exoplanets—Biosignatures—Habitability markers—Photosynthesis—Planetary surfaces—Atmospheres—Spectroscopy—Cryptic biospheres—False positives
Issue or Number:6
Record Number:CaltechAUTHORS:20180514-100842377
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Official Citation:Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life. Schwieterman Edward W., Kiang Nancy Y., Parenteau Mary N., Harman Chester E., DasSarma Shiladitya, Fisher Theresa M., Arney Giada N., Hartnett Hilairy E., Reinhard Christopher T., Olson Stephanie L., Meadows Victoria S., Cockell Charles S., Walker Sara I., Grenfell John Lee, Hegde Siddharth, Rugheimer Sarah, Hu Renyu, and Lyons Timothy W. Astrobiology 2018 18:6, 663-708
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86388
Deposited By: Tony Diaz
Deposited On:16 May 2018 14:25
Last Modified:15 Nov 2021 20:38

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