@article{cad23a9641234841bbef1e679e1d245d,
title = "Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life",
abstract = "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.",
keywords = "Atmospheres, Biosignatures, Cryptic biospheres, Exoplanets, False positives, Habitability markers, Photosynthesis, Planetary surfaces, Spectroscopy",
author = "Schwieterman, {Edward W.} and Kiang, {Nancy Y.} and Parenteau, {Mary N.} and Harman, {Chester E.} and Shiladitya Dassarma and Fisher, {Theresa M.} and Arney, {Giada N.} and Hilairy Hartnett and Reinhard, {Christopher T.} and Olson, {Stephanie L.} and Meadows, {Victoria S.} and Cockell, {Charles S.} and Sara Walker and Grenfell, {John Lee} and Siddharth Hegde and Sarah Rugheimer and Renyu Hu and Lyons, {Timothy W.}",
note = "Funding Information: 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 Palle. Finally, the authors are thankful for the helpful comments from two anonymous referees, which allowed us to further improve the paper. Funding Information: 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 Pall{\'e}. Finally, the authors are thankful for the helpful comments from two anonymous referees, which allowed us to further improve the paper. Publisher Copyright: {\textcopyright} 2018 Edward W. Schwieterman et al.",
year = "2018",
month = jun,
doi = "10.1089/ast.2017.1729",
language = "English (US)",
volume = "18",
pages = "663--708",
journal = "Astrobiology",
issn = "1531-1074",
publisher = "Mary Ann Liebert Inc.",
number = "6",
}