16 September 2026: Yueyun Ouyang and Ruizhi Zhan

Speakers: Yueyun Ouyang (PKU/Oxford) and Ruizhi Zhan (PKU/Cambridge)

Date: Wednesday 16 September 2026

Time: 14:00

Location: Physics 3.21 (Berry)

Yueyun Ouyang: Retention of Surface Water on Rocky Planets in the Venus Zone around M Dwarfs

Terrestrial planets in the Venus zone around M dwarfs may retain surface ice on their permanent nightsides if atmospheric heat transport is inefficient, potentially allowing regional habitability. However, the amount of water available to form such ice is constrained by condensation from a steam atmosphere during or after a runaway greenhouse state, and the mechanism triggering this condensation remains unclear. Here, we use a two-column moist radiative–convective–subsiding model to investigate the water condensation process on tidally locked planets from the runaway greenhouse state. We find that the water condensation process is characterized by two distinct equilibrium states under the same incoming stellar flux. The initiation of condensation corresponds to a warm, unstable state exhibiting positive Planck feedback, whereas the termination phase corresponds to a cold, stable state exhibiting negative Planck feedback. We further show that the surface water mass in the collapsed state decreases with the incoming stellar flux, background surface pressure, and optical thickness of noncondensable greenhouse gases, with a global equivalent depth of less than ∼20 cm. Our two-column approach provides a straightforward way to understand the water evolution on Venus zone planets around M dwarfs.

Ruizhi Zhan: Reinterpreting the JWST Observations of 55 Cancri e with a Non-Grey General Circulation Model

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). So far, these observations have only been interpreted using 1D models without self-consistent heat redistribution, as the planet’s extreme temperatures make it inaccessible to most 3D models. Here we perform cloud-free GCM simulations of 55 Cancri e using custom correlated-k coefficients developed from the ExoMol database. Our best-fit simulations match the JWST spectra from Hu et al. (2024) 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 atmosphere, which were previously proposed based on 1D models (Hu et al. 2024; Zilinskas et al. 2025). We also find 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 (e.g. 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.