Atmospheric Seasonality as an Exoplanet Biosignature

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.

arXiv comment12 pages, 5 figures

References in corpus (12)

• Habitable Zones Around Main-Sequence Stars: New Estimates
• Extreme Water Loss and Abiotic O${}_2$ Buildup On Planets Throughout the Habitable Zones of M Dwarfs
• The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth
• Abiotic Ozone and Oxygen in Atmospheres Similar to Prebiotic Earth
• Abiotic O${}_2$ Levels on Planets around F, G, K, and M Stars: Possible False Positives for Life?
• The Habitability of Proxima Centauri b: II: Environmental States and Observational Discriminants
• Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets
• Detection of Ocean Glint and Ozone Absorption Using LCROSS Earth Observations
• Identifying Planetary Biosignature Impostors: Spectral Features of CO and O4 Resulting from Abiotic O2/O3 Production
• False negatives for remote life detection on ocean-bearing planets: Lessons from the early Earth
• Detecting and Constraining N${}_2$ Abundances in Planetary Atmospheres Using Collisional Pairs
• Evolution of Earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early Earth analog planets with a coupled atmosphere biogeochemical model

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• A Geologically Robust Procedure For Observing Rocky Exoplanets to Ensure that Detection of Atmospheric Oxygen is an Earth-Like Biosignature
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