Séminaire IPAG

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The diversity of outer icy bodies revealed by JWST and its link to early Solar System processes

jeudi 12 mars 2026 - 11h15

Rosario Brunetto - IAS
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Trans-Neptunian Objects (TNOs) are remnants of planetary formation, but most of them were later affected by the giant planet instability, with the remarkable exception of the so-called “Cold Classical” population. Using the James Webb Space Telescope’s NIRSpec instrument, near-infrared spectra of over one hundred medium-sized TNOs, Centaurs and Neptune Trojans were obtained in the past few years, offering the largest and most diverse spectral dataset of icy bodies in the outer Solar System to date. Our analysis reveals three main compositional groups, shaped by absorption features of H₂O, CO₂, CH₃OH, and complex organic materials. Variations in band areas among these molecules highlight distinct spectral groupings and sub-categories. Interestingly, the group with the strongest CH₃OH, H₂O, and CO₂ signatures excludes the Cold Classical TNOs, which cluster separately. Other dynamical classes (e.g., Resonant, Scattering, Detached, Centaurs) display a mix of spectral types with no consistent correlation between dynamics and composition. Most TNO surfaces show significant deviations from the protoplanetary and cometary ice compositions, indicating that evolutionary processes altered TNO surfaces early on. Sharp transitions between spectral groups suggest early sculpting - likely from ancient icelines - such as a pre-accretional CO iceline in the disk or post-accretional CO₂/CH₃OH retention icelines before planetary migration. These results reshape our understanding of the early Solar System and the processes that set the chemical makeup of its most distant bodies.

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