Utilizing 3D GCMs to reinterpret JWST observations of 55 Cancri e.

Tue, 20 May 2025 00:00:00 +0000

Recent observations of 55 Cancri e suggest an atmosphere rich in CO or CO₂ ( ); other observations indicate the planet’s eclipse depth is highly variable (e.g. ).

Thermal emission spectrum of 55 Cancri e ( ). 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 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 ( ; ).

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 ( ), 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.

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JWST | Ruizhi Zhan

Utilizing 3D GCMs to reinterpret JWST observations of 55 Cancri e.