Séminaire IPAG

Forming Planets and their Moons: Establishing an Observational View of Circumplanetary Disks

jeudi 21 mai 2026 - 11h00
Gabriele Cugno - Zurich U.
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During the final assembly of gas giant planets, circumplanetary disks (CPDs) of gas and dust form as a natural consequence of angular momentum conservation. These structures regulate how material is accreted onto the planet and contain the ingredients for the formation of satellite systems. Yet, the composition of CPDs has remained largely unconstrained: their faint emission and close angular separation from their host stars have historically placed them beyond the reach of detailed spectroscopic characterization. By applying advanced high-contrast post-processing techniques to data from JWST/MIRI Medium-Resolution Spectrograph (MRS), we can now directly access and characterize this reservoir for wide-orbit planetary-mass companions for the first time. In this talk, I present the first medium-resolution molecular spectrum (12–16 μm) of a disk surrounding a planetary-mass companion. The spectrum of CT Cha b reveals the elemental and molecular content of its circumplanetary material, enabling a direct comparison with the atmospheric composition of the companion and providing new constraints on its accretion history. Striking chemical differences between the disk around the companion and the circumstellar disk around CT Cha point to rapid and divergent chemical evolution on Myr timescales. These results form the foundation of an ongoing JWST Cycle 4 survey designed to move from individual detections to a population-level characterization of CPDs. In this program, we target the complete sample of circumplanetary disks accessible to MIRI/MRS, building the first homogeneous spectroscopic census of their gas and dust content. I will present the first results emerging from this survey, showing how CPD chemistry and physical properties evolve with system age and environment, and demonstrating how this new population view provides critical empirical anchors for models of giant planet growth, disk accretion, and moon formation.
Hôtes : Mickael Bonnefoy

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