biostudies-literatureUnknown119(14)Thompson MAMethane has been proposed as an exoplanet biosignature. Imminent observations with the James Webb Space Telescope may enable methane detections on potentially habitable exoplanets, so it is essential to assess in what planetary contexts methane is a compelling biosignature. Methane’s short photochemical lifetime in terrestrial planet atmospheres implies that abundant methane requires large replenishment fluxes. While methane can be produced by a variety of abiotic mechanisms such as outgassing, serpentinizing reactions, and impacts, we argue that—in contrast to an Earth-like biosphere—known abiotic processes cannot easily generate atmospheres rich in CH4 and CO2 with limited CO due to the strong redox disequilibrium between CH4 and CO2. Methane is thus more likely to be biogenic for planetProceedings of the National Academy of Sciences of the United States of Americae2117933119https://www.ebi.ac.uk/biostudies/studies/S-EPMC9168929biostudies-literatureThe case and context for atmospheric methane as an exoplanet biosignature.PMC9168929Thompson MAWogan NTelus MKrissansen-Totton JFortney JJfalseThe case and context for atmospheric methane as an exoplanet biosignature.Methane has been proposed as an exoplanet biosignature. Imminent observations with the James Webb Space Telescope may enable methane detections on potentially habitable exoplanets, so it is essential to assess in what planetary contexts methane is a compelling biosignature. Methane’s short photochemical lifetime in terrestrial planet atmospheres implies that abundant methane requires large replenishment fluxes. While methane can be produced by a variety of abiotic mechanisms such as outgassing, serpentinizing reactions, and impacts, we argue that—in contrast to an Earth-like biosphere—known abiotic processes cannot easily generate atmospheres rich in CH4 and CO2 with limited CO due to the strong redox disequilibrium between CH4 and CO2. Methane is thus more likely to be biogenic for planet2022-01-01T00:00:00Z2022 Apr2025-04-19T17:49:32.389Z2024-10-18T21:31:49.27ZS-EPMC91689293535362710.1073/pnas.2117933119