Webb Telescope Detects Methane on Interstellar Comet 3I/ATLAS (esa.int)

• Webb detected methane on interstellar comet 3I/ATLAS using MIRI's medium resolution spectrometer.
• Methane was observed only after the comet's perihelion, indicating subsurface origin.
• High relative abundances of methane and carbon dioxide compared to water suggest a different formation environment.

"The NASA/ESA/CSA James Webb Space Telescope has detected methane gas on interstellar comet 3I/ATLAS for the first time on an interstellar visitor. Using MIRI's medium resolution spectrometer, Webb observed the comet on 15-16 December and 27 December 2025 as it exited the Solar System. Methane was found only after the comet's close pass to the Sun, suggesting it was buried beneath the surface. The relative abundance of methane and carbon dioxide compared to water is unusually high, indicating a different formation environment than typical Solar System comets. The findings were published in The Astrophysical Journal Letters."