Modeling the Atmosphere of 55 Cancri e with a Non-grey General Circulation Model

The ultra-short period super Earth 55 Cancri e offers a unique opportunity to study a small exoplanet and its potential atmosphere. Despite extensive observation, however, the nature of 55 Cancri e’s atmosphere is still poorly understood. These observational challenges are made worse by a lack of clear theoretical predictions for the atmospheric circulations of hot rocky exoplanets. So far, few 3D models with realistic radiative transfer have been applied to the high-temperature regime relevant for 55 Cancri e, largely because most 3D general circulation model (GCM) radiative transfer codes break down at high temperatures. Here we develop custom correlated-k coefficients from the ExoMol line list dataset. Then we perform 3D GCM simulations with non-grey radiative transfer to model the atmosphere on 55 Cancri e. Comparing our simulations to recent eclipse spectra from JWST MIRI (Hu et al. 2024), we suggest the atmosphere of 55 Cancri e is more likely to be thick and carbon dioxide rich, a different conclusion than that based on 1D retrieval models. In addition, our clearsky simulations suggest that 55 Cancri e’s atmosphere should exhibit time variability. However, the simulated variability is much weaker than that seen in observations from Spitzer, CHEOPS, and JWST. Our work rules out large-scale atmospheric dynamics as the cause of 55 Cancri e’s observed variability, favoring other mechanisms. More broadly, our work presents a new non-grey 3D GCM for hot rocky exoplanets and provides a more realistic framework for investigating the atmosphere of ultra-hot exoplanets like 55 Cancri e.