James Webb Telescope detects methane on comet 3I/Atlas
Methane has been detected on comet 3I/Atlas. It is the first detection of methane on an interstellar comet.
Hubble image of 3I/ATLAS
(Image: NASA, ESA, STScI, D. Jewitt (UCLA), M.-T. Hui (Shanghai Astronomical Observatory). Image Processing: J. DePasquale (STScI))
Scientists have created a chemical fingerprint of comet 3I/Atlas using the James Webb Space Telescope (JWST). It is the first chemical fingerprint of an interstellar object in the mid-infrared range.
The telescope's Mid-Infrared Instrument (Miri) detected carbon dioxide, water vapor, and methane. Carbon monoxide, methanol, and hydrogen cyanide had already been detected previously. The observations took place from December 15 to 16 and on December 27, when the comet was 330 million and 380 million kilometers from the Sun, respectively. At that time, the comet had already passed its closest point to the sun and was on its way out of the solar system.
(Image:Â NASA, ESA, CSA, STScI, M. Belyakov (Caltech), I. Wong (STScI), Image Processing: A. Pagan (STScI) (CC BY 4.0))
Methane was detected directly on an interstellar celestial body for the first time. The fact that it was found relatively late suggests that it had been hidden beneath the comet's surface. This protected it from evaporation. Only during its flyby did the Sun's heat reach deeper parts of the outer shell. This caused the methane to be released through sublimation. This means that the methane transitions directly from a solid to a gaseous state.
Large amount of carbon dioxide and methane
It is remarkable that the amount of carbon dioxide and methane is unusually high compared to the amount of water, the ESA announced. 3I/Atlas also released more carbon dioxide relative to water than comets from our solar system, proposing that the conditions under which 3I/Atlas formed are significantly different from those in our solar system. The team led by Matthew Belyakov from the California Institute of Technology in Pasadena describes their findings in the journal The Astrophysical Journal.
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3I/Atlas was only the third known interstellar visitor to our solar system. With a diameter of around 2.6 kilometers, it is larger than its predecessors 1I/’Oumuamua and 2I/Borisov, as well as faster and probably older than them.
3I/Atlas was discovered in early July 2025 – the designation 3I stands for the third known celestial body from interstellar space, “Atlas” (Asteroid Terrestrial-impact Last Alert System) is an automatic early warning system for asteroids. 3I/ATLAS came closest to Earth at the end of last year. However, the encounter was harmless: it passed our planet at a distance of a good 270 million kilometers. After traversing the solar system, it will never return.
(wpl)
