JWST Finds 3I/ATLAS Methane Ratio 13 Times 67P's, Pointing to 7-Billion-Year-Older Origin
Updated
Updated · ScienceAlert · Oct 31
JWST Finds 3I/ATLAS Methane Ratio 13 Times 67P's, Pointing to 7-Billion-Year-Older Origin
3 articles · Updated · ScienceAlert · Oct 31
Summary
NASA-led researchers used the James Webb Space Telescope to measure comet 3I/ATLAS's methane deuterium-to-hydrogen ratio and found it exceeds any known Solar System body.
That methane signature is 13 times higher than comet 67P's secure benchmark, indicating the interstellar comet's ices formed in an extremely cold, low-metallicity environment under intense cosmic-ray exposure.
Late-December 2025 observations caught 3I/ATLAS about 2.5 times Earth’s distance from the Sun, where warming sunlight was driving off gases from its coma for infrared analysis.
Low carbon-13 levels also point to exceptional age, with researchers saying the object may have formed more than 7 billion years before the Sun and perhaps near one of the Milky Way's oldest stars.
The Nature Astronomy study casts 3I/ATLAS as a rare preserved sample from an ancient exosolar nursery, offering a direct probe of chemistry usually hidden inside opaque planet-forming regions.