The Coupled Impacts of Atmospheric Composition and Obliquity on the Climate Dynamics of TRAPPIST-1e

Numerous previous studies have evaluated the climate state of temperate rocky exoplanets, but few have explored the implications of varying obliquity. JWST will use transmission spectroscopy to characterize TRAPPIST-1e, so comprehensive pictures of its possible climate states are important to be able to compare to such observations. Planets in multi-planet systems are expected to migrate as resonant-chains, thus allowing them to undergo planet-planet interactions and possibly maintain a non-zero obliquity. The TRAPPIST-1 system is in such a near resonant configuration, making it plausible that TRAPPIST-1e has a non-zero obliquity. Here we use ExoCAM to study the possible climates of TRAPPIST-1e at varying obliquities and atmospheric compositions. We vary obliquity from 0 to 90 degrees, assuming spin synchronization in all cases. We also vary the partial pressure of carbon dioxide from 0.004 bars (modern Earth) to 1 bar with a fixed Earth-like complement of nitrogen and methane. We find that models with a higher obliquity are hotter overall and have a smaller day-night temperature contrast than the lower obliquity models, which is consistent with previous studies. As obliquity increases, the Walker-like overturning circulation becomes more vertically extended and the locations of the ascending and descending branches change. The obliquity also impacts the strength of cloud-radiative and ice albedo feedbacks and can significantly affect the general climate states. Additionally, as the amount of carbon dioxide increases, the climate of TRAPPIST-1e becomes hotter, cloudier, and less variable. Overall, our results show that non-zero obliquity can greatly impact the mean climate state of rocky planets orbiting late-type M-dwarf stars.