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Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar SystemSome atmospheric gases have been proposed as counter indicators to the presence of life on an exoplanet if remotely detectable at sufficient abundance (i.e., antibiosignatures), informing the search for biosignatures and potentially fingerprinting uninhabited habitats. However, the quantitative extent to which putative antibiosignatures could exist in the atmospheres of inhabited planets is not well understood. The most commonly referenced potential antibiosignature is CO, because it represents a source of free energy and reduced carbon that is readily exploited by life on Earth and is thus often assumed to accumulate only in the absence of life. Yet, biospheres actively produce CO through biomass burning, photooxidation processes, and release of gases that are photochemically converted into CO in the atmosphere. We demonstrate with a 1D ecosphere-atmosphere model that reducing biospheres can maintain CO levels of approximately 100 ppmv (parts per million by volume) even at low H2 fluxes due to the impact of hybrid photosynthetic ecosystems. Additionally, we show that photochemistry around M dwarf stars is particularly favorable for the buildup of CO, with plausible concentrations for inhabited, oxygen-rich planets extending from hundreds of ppm to several percent. Since CH4 buildup is also favored on these worlds, and because O2 and O3 are likely not detectable with the James Webb Space Telescope, the presence of high CO (greater than 100 ppmv) may discriminate between oxygen-rich and reducing biospheres with near-future transmission observations. These results suggest that spectroscopic detection of CO can be compatible with the presence of life and that a comprehensive contextual assessment is required to validate the significance of potential antibiosignatures.
Document ID
20190002356
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.3847/1538-4357/ab05e1
Authors
Schwieterman, Edward W. (California Univ. Riverside, CA, United States)
Reinhard, Christopher T. (California Univ. Riverside, CA, United States)
Olson, Stephanie L. (California Univ. Riverside, CA, United States)
Ozaki, Kazumi (California Univ. Riverside, CA, United States)
Harman, Chester E. (California Univ. Riverside, CA, United States)
Hong, Peng K. (Chiba Institute of Technology Narashino, Chiba, Japan)
Lyons, Timothy W. (California Univ. Riverside, CA, United States)
Date Acquired
April 11, 2019
Publication Date
March 15, 2019
Publication Information
Publication: The Astrophysical Journal
Publisher: IOP Science / American Astronomical Society
Volume: 874
Issue: 1
ISSN: 2041-8205
e-ISSN: 2041-8213
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
GSFC-E-DAA-TN66978
Funding Number(s)
CONTRACT_GRANT: NNA13AA93A
CONTRACT_GRANT: NNA15BB03A
CONTRACT_GRANT: 80NSSC18K0829
CONTRACT_GRANT: 80NSSC18M0133
CONTRACT_GRANT: NNH13ZDA017C
Distribution Limits
Public
Copyright
Use by or on behalf of the US Gov. Permitted.
Keywords
Earth
Planets and Satellites: Terrestrial Planets
Planets and Satellites: Atmospheres
Techniques: Spectroscopic
Astrobiology

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