JWST Detects Methane on Interstellar Comet 3I/ATLAS, Revealing New Chemistry

NASA’s James Webb Space Telescope detected methane in the interstellar comet 3I/ATLAS using the MIRI instrument, marking the first direct methane fingerprint on an interstellar object; the methane-to-water ratio is unusually high and CO2 is also abundant, pointing to a different formation environment than typical solar system comets. Methane appears buried beneath the surface and released as the comet heats near the Sun, while water vapor dissociates more widely in the coma; two observations show gas production declining with distance from the Sun, with methane and CO2 concentrated near the nucleus.