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Arxiv: Unveiling the ice and gas nature of active centaur (2060) Chiron using the James Webb Space Telescope Published: 7/10/2024 6:39:26 PM Updated: 7/10/2024 6:39:26 PM

Paper abstract: (2060) Chiron is a large centaur that has been reported active on multipleoccasions including during aphelion passage. Studies of Chirons coma duringactive periods have resulted in the detection of C(triple)N and CO outgassing.Significant work remains to be undertaken to comprehend the activationmechanisms on Chiron and the parent molecules of the gas phases detected. Thiswork reports the study of the ices on Chirons surface and coma and seeksspectral indicators of volatiles associated with the activity. Additionally, wediscuss how these detections could be related to the activation mechanism forChiron and, potentially, other centaurs. In July 2023, the James Webb SpaceTelescope (JWST) observed Chiron when it was active near its aphelion. Wepresent JWST/NIRSpec spectra from 0.97 to 5.27 microns with a resolving powerof 1000, and compare them with laboratory data for identification of thespectral bands. We report the first detections on Chiron of absorption bands ofseveral volatile ices, including CO2, CO, C2H6, C3H8, and C2H2. We also confirmthe presence of water ice in its amorphous state. A key discovery arising fromthese data is the detection of fluorescence emissions of CH4, revealing thepresence of a gas coma rich in this hyper-volatile molecule, which we alsoidentify to be in non-local thermal equilibrium (nonLTE). CO2 gas emission isalso detected in the fundamental stretching band at 4.27 microns. We argue thatthe presence of CH4 emission is the first proof of the desorption of CH4 due toa density phase transition of amorphous water ice at low temperature inagreement with the estimated temperature of Chiron during the JWST observations(61 K). Detection of photolytic and proton irradiation products of CH4 and CO2on the surface, in the coma ice grains, or in the ring material is alsodetected via a forest of absorption features from 3.5 to 5.3 microns.