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Atmospheric Seasonality as an Exoplanet Biosignature

Research output: Contribution to journalArticle

  • Stephanie L. Olson
  • Edward W. Schwieterman
  • Christopher T. Reinhard
  • Andy Ridgwell
  • Stephen R. Kane
  • Victoria S. Meadows
  • Timothy W. Lyons
Original languageEnglish
Article numberL14
JournalAstrophysical Journal Letters
Volume858
Issue number2
Early online date9 May 2018
DOIs
DateAccepted/In press - 30 Apr 2018
DateE-pub ahead of print - 9 May 2018
DatePublished (current) - 10 May 2018

Abstract

Current investigations of exoplanet biosignatures have focused on static evidence of life, such as the presence of biogenic gases like O2 or CH4. However, the expected diversity of terrestrial planet atmospheres and the likelihood of both "false positives" and "false negatives" for conventional biosignatures motivate exploration of additional life detection strategies, including time-varying signals. Seasonal variation in atmospheric composition is a biologically modulated phenomenon on Earth that may occur elsewhere because it arises naturally from the interplay between the biosphere and time-variable insolation. The search for seasonality as a biosignature would avoid many assumptions about specific metabolisms and provide an opportunity to directly quantify biological fluxes - allowing us to characterize, rather than simply recognize, biospheres on exoplanets. Despite this potential, there have been no comprehensive studies of seasonality as an exoplanet biosignature. Here, we provide a foundation for further studies by reviewing both biological and abiological controls on the magnitude and detectability of seasonality of atmospheric CO2, CH4, O2, and O3 on Earth. We also consider an example of an inhabited world for which atmospheric seasonality may be the most notable expression of its biosphere. We show that life on a low O2 planet like the weakly oxygenated mid-Proterozoic Earth could be fingerprinted by seasonal variation in O3 as revealed in its UV Hartley-Huggins bands. This example highlights the need for UV capabilities in future direct-imaging telescope missions (e.g., LUVOIR/HabEx) and illustrates the diagnostic importance of studying temporal biosignatures for exoplanet life detection/characterization.

    Research areas

  • astrobiology, Earth, planets and satellites: atmospheres, planets and satellites: terrestrial planets, techniques: spectroscopic

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via IoP at https://doi.org/10.3847/2041-8213/aac171 . Please refer to any applicable terms of use of the publisher.

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    Licence: CC BY

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