Interstellar comet 3I/ATLAS is blasting out a bunch of methane. Here's why that's weird

Methane has been seen spewing from comet 3I/ATLAS, marking the first time that the gas has been identified on an interstellar object. The amount of methane, relative to water, is also larger than is typically seen in comets from our solar system, further highlighting how different this interstellar visitor is than objects from our own cosmic neighborhood. The James Webb Space Telescope (JWST) initially observed the interstellar comet with its Mid-Infrared Instrument (MIRI) on Dec. 15-16 2025, when 3I/ATLAS was 205 million miles (330 million kilometers or 2.20 astronomical units ) from the sun . However, there was a problem with two of the observations, which failed to acquire a guide-star in order for the telescope to point accurately. This meant that those two observations had to be repeated later, on Dec. 27, when 3I/ATLAS was 236 million miles (380 million km or 2.54 AU) from the sun. As it happened, these repeat observations turned out to be quite fortuitous. Both sets of observations came less than two months after 3I/ATLAS had reached perihelion – its closest point to the sun – on Oct. 29, 2025. The extra heating from the sun had warmed the comet’s surface, increasing the amount of outgassing from the comet, but the level of outgassing was beginning to decrease as the comet moved away. MIRI detected water vapor streaming at large distances from the comet's nucleus as icy grains in the coma (the gaseous ‘atmosphere’ surrounding the comet’s solid nucleus) vaporized. …