Por Diogo Quirino (IA-FCUL).

Transmissão online via Microsoft Teams (pw: HS6Yg2Cz).

Abstract: Defining the cosmic shoreline, the orbital distance separating planets with secondary atmospheres from those without, is a compelling question in exoplanetary science. Earth-sized planets orbiting low-mass stars are the best candidates for atmospheric detection. Due to the host star's lower luminosity, Earth-like stellar irradiations are found at much closer orbital distances. Conversely, their lifelong strong stellar activity might drive atmospheric erosion on close-in planets. Thus, the observational bias becomes the detection challenge.

High mean molecular weight secondary atmospheres, particularly CO2-dominated ones, offer the best resilience against escape processes. One system in particular, TRAPPIST-1, might hold the clues for this atmospheric conundrum. At 12 pc (40 light-years) from Earth, TRAPPIST-1 hosts at least seven transiting Earth-sized planets, orbiting a low-mass star, over a wide range of stellar irradiations (4.153 – 0.144x Solar constant). Recent observations with the James Webb Space Telescope (JWST) suggest that the second innermost planet, TRAPPIST-1c, does not possess a Venus-like atmosphere despite receiving a similar stellar irradiation. Here, we use a 3D general circulation model (GCM), the Generic-PCM, to simulate a modern Venus-like atmosphere on TRAPPIST-1c and to provide synthetic observables that support the conclusions drawn from JWST. In our quest, we focus on the third planet, TRAPPIST-1d, right at the inner edge of the Habitable Zone, where tantalising new evidence suggests that a cloudy, Venus-like atmosphere might be lurking. We will explore the large-scale circulation and thermal structure of such an atmosphere and discuss its detection prospects.