There’s More to Life in Reflected Light: Simulating the Detectability of a Range of Molecules for High-contrast, High-resolution Observations of Nontransiting Terrestrial Exoplanets

Abstract The upcoming extremely large telescopes (ELTs) will provide the first opportunity to search for signs of habitability and life on nontransiting terrestrial exoplanets using high-contrast, high-resolution instrumentation. However, the suite of atmospheric gases in terrestrial exoplanet environments that are accessible to ground-based reflected light observations has not been thoroughly explored. In this work, we use an upgraded ELT detectability pipeline to simulate the detectability of gases that can serve as habitability markers, potential biosignatures, and false-positive discriminants in the atmospheres of Earth-sized and sub-Neptune planets. We calculate molecular detectability for five photochemically self-consistent atmosphere types, including the modern and Archean Earth, uninhabited biosignature “false-positive” environments, and a sub-Neptune, over a grid of observational configurations for nontransiting targets within 10 pc of Earth. For the most accessible nearby target, Proxima Centauri b, our results suggest that we may be able to rule out a sub-Neptune atmosphere in as little as a single hour of observing, and two biosignature disequilibrium pairs (O 2 /CH 4 and CO 2 /CH 4 ) may be accessible in ∼10 hr for the most optimistic scenario. It may also be possible to discriminate uninhabited worlds and rule out biosignature false positives by identifying contextual indicators (CO and H 2 O) of abiotic O 2 and/or CH 4 buildup on similar timescales. In the near term, ELT reflected light observations will likely allow us to characterize multiple nearby terrestrial atmospheres and ultimately search for signs of habitability and life.