We present unprecedented findings on (2060) Chiron using James Webb Space Telescope (JWST) NIRSpec imaging and spectroscopy from cycle 1 GTO program 1273. Our study (Pinilla-Alonso et al. 2024 A&A Letter) marks the first detection of carbon dioxide (CO2) and methane (CH4) active outgassing and coma emission at heliocentric distances of ~18 au. These discoveries challenge existing paradigms of activation mechanisms for comets and centaurs, particularly with the coexistence of CH4 and CO2 gases and carbon monoxide (CO) ice. Our spectroscopic images clearly demonstrate active sublimation processes driven by solar heating, with CH4 emanating from regions receiving high solar insolation. The lack of CH4 ice absorptions in Chiron's spectrum indicates a subsurface reservoir. We suggest that this observation is the first proof of the desorption of CH4 due to a density phase transition of amorphous water ice at low temperature, in agreement with the estimated temperature of Chiron during the JWST observations (61 K).

The presence of irradiation byproducts of CH4, CO2, and CO in both reducing e.g., acetylene (C2H2), ethane (C2H6), propane (C3H8) and oxidizing e.g., carbon trioxide (CO3) conditions adds an extra level of complication. Notably absent are molecules resulting from CH and CO irradiation such as H2CO, CH3CHO, or CH3COOH, suggesting potential physical or temporal separation between CH4 and CO2 reservoirs.

These findings advance our understanding of Chiron's ice and gas phases, shedding light on centaur and comet activation mechanisms and thermophysical evolution.Dynamical models indicate Chiron's recent injection into the planetary region, making it a pivotal specimen for studying early surface thermal evolution among carbon-rich centaurs and young comets. Additional spectra of Chiron's nucleus and coma in the future could provide insights into its secular evolution.