Utilizing 3D GCMs to reinterpret JWST observations of 55 Cancri e.
Recent observations of 55 Cancri e suggest an atmosphere rich in CO or CO2 (Hu et al. 2024); other observations indicate the planet’s eclipse depth is highly variable (e.g. Patel et al. 2024).
Thermal emission spectrum of 55 Cancri e (Hu et al. 2024). The best-fit models are a blackbody or a CO2–N2, CO2–CO, or CO-only atmosphere with varied composition and pressure–temperature profiles.
So far, these observations have only been interpreted using 1D models without self-consistent heat redistribution. We apply GCM simulations with custom non-grey radiative transfer to reinterpret JWST observations of 55 Cancri e.
GCM simulations compared with the JWST thermal-emission spectrum of 55 Cancri e.
Our best-fit simulations match the JWST spectra well, favoring an atmosphere that is both thick (≥ 10 bar) and CO2-rich (> 1% CO2 volume mixing ratio), while ruling out thin (< 10 bar) and pure-CO/CO2-poor atmospheres, which were previously proposed based on 1D models (Hu et al. 2024; Zilinskas et al. 2025).
We also find that large-scale atmospheric dynamics, i.e., weather, is insufficient to explain the observed variability. A thick, CO2-rich atmosphere implies that 55 Cancri e likely formed with significantly more volatiles than Earth and Venus. In addition, a thick atmosphere makes it unlikely that the planet’s variability is caused by transient outgassing (Heng 2023), favoring other variability mechanisms such as clouds. Our work provides model constraints for upcoming JWST observations of 55 Cancri e and highlights the importance of interpreting thermal-emission observations with self-consistent 3D models.