JWST Uncovers Methane in Interstellar Comet 3I/ATLAS, Hinting at Hidden Chemistry

Using JWST's MIRI instrument, astronomers directly detected methane in the coma of interstellar comet 3I/ATLAS—the first methane detection in an ISO. The methane-to-water ratio is unusually high, while carbon dioxide remains abundantly released near the nucleus, reinforcing 3I/ATLAS’s CO2-rich chemistry and signaling formation conditions outside our Solar System. Complementary detections from Hubble, ALMA, and SPHEREx show a ranging volatile inventory, including cyanogen, nickel, methanol, and HCN; near-infrared data reveal water, CO2, and CO. Methane likely sublimated from subsurface ice as the comet heated near perihelion, pointing to a formation history unlike typical Solar System comets. The findings appear in ApJL 2026 by Belyakov et al.