Outgassing Predictions for TRAPPIST-1 and Implication for Methane Biosignatures

Abstract:

The search for life beyond the solar system necessitates understanding the atmospheres of rocky exoplanets that reside in the habitable zone. An important component of building and maintaining an atmosphere is mantle outgassing. The TRAPPIST-1 system of seven Earth-sized, rocky exoplanets provides an opportunity to observe the outgassing products of terrestrial planets. Mass-radius observations suggest that the habitable zone TRAPPIST-1 planets are potentially volatile rich “waterworlds” with substantial inventories of surface water. Here, we explore the relationship between ocean depth and outgassed species to make predictions for plausible atmospheric compositions testable with the James Webb Space Telescope. We focus on the potential for high pressure methane outgassing as a potential false positive for biogenic methane. We calculate the fraction of methane to expect from volcanic activity to provide a limit on what could be biogenic methane or what is more likely non-biogenic methane. These calculations expand understanding of methane outgassing on waterworlds and help provide testable predictions for future spectroscopic observations using James Webb Space Telescope in the search for biogenic methane on TRAPPIST-1 and elsewhere.