Anticipating biosignatures false positives in the 2020s
University of Washington
The James Webb Space Telescope and ground based Extremely Large Telescopes will provide the first opportunities to characterize the atmospheres of rocky exoplanets and detect potential biosignature gases. For the biosignature gases that are most readily detectable?specifically methane, oxygen, and ozone?a range of non-biological production mechanisms have been proposed. Arguably, detection of these so-called biosignature false positives is more likely this decade than finding genuine signs of life. Nonetheless, confident life detection in the more distant future will require an improved understanding of these imminently detectable false positive scenarios and, more broadly, of the probable geochemical evolution of lifeless worlds. Here, I will present a generalized model of rocky planet evolution that connects early magma ocean evolution to subsequent, temperate geochemical cycling. The thermal evolution of the interior, tectonic recycling of volatiles, surface climate, and atmospheric escape are explicitly coupled throughout this evolution. The model has been validated against Solar System planets and applied to anticipate abiotic oxygen accumulation for both temperate and highly irradiated rocky exoplanets. Preliminary predictions for Trappist-1 b-h, GJ 1132 b, and LP 890-9 b-c will be presented. Methane biosignatures and their probable false positives will also be considered for these characterizable exoplanets. While methane can be produced by a variety of abiotic mechanisms such as magmatic outgassing, water-rock reactions, metamorphic reactions, and impacts, in contrast to an Earth-like biosphere, known abiotic processes cannot easily generate atmospheres rich in both CH4 and CO2 with limited CO due to the strong redox disequilibrium between CH4 and CO2. I will further argue that an understanding of terrestrial planets?both solar system and extra solar?as a unified class of objects will be necessary to enable future life detection.
Date: Thursday, 20 October 2022 Time: 11:30 Where: Université de Montréal Campus MIL salle A3541 - Diffusion sur Zoom