JWST observations of Chiron: A unique active Centaur beyond 18 AU
Session 12.06 Spectroscopy
Friday 06-28 | 11:20 - 11:40

Centaurs are inward-scattered objects from the Kuiper belt that orbit within the giant planet region. Their closer heliocentric distances compared to Kuiper belt objects enable more detailed explorations of the surface properties of outer solar system bodies. Meanwhile, the higher levels of irradiation provide a unique window into the effects of thermal processing on the surface properties of icy planetesimals. Chiron is one of the largest Centaurs, with a mean radius of 90 km. Notably, Chiron belongs to the enigmatic subpopulation of active Centaurs and has displayed cometary activity several times since its discovery. In March 2021, Chiron underwent an outburst while it was at a heliocentric distance of 18.8 AU. This report of Centaur activity is the most distant to date by a significant margin and challenges our prevailing understanding of the mechanisms that trigger and sustain outgassing on these objects. A holistic picture of Chiron's surface and coma promises to revolutionize our understanding of Centaur activity and the properties of primitive icy planetesimals near and far. In January 2024, we obtained observations of Chiron with the Near Infrared Spectrograph on JWST as part of Cycle 2 Director's Discretionary Time (DDT) Program 4621 (PI: Ian Wong), following up on earlier spectra from Cycle 1 Guaranteed Time Observation Program 1273 (PI: Jonathan Lunine). The higher-spectral-resolution DDT spectra span 1.7 – 5.1 microns and reveal a wide range of surface ices. The spatial information from the integral field unit also yields detailed maps of individual molecular constituents within the coma. In this talk, I will present the results of our DDT observations of Chiron, place them within the context of other active bodies observed with JWST, and discuss the broader implications for our understanding of distant cometary activity and the formation and evolution of icy planetesimals throughout the Solar System.

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