Webb Telescope finds methane on interstellar comet 3I/ATLAS
The James Webb Space Telescope has captured the first direct infrared chemical fingerprint of an interstellar object, revealing the unusual composition of comet 3I/ATLAS— the messenger of another star system. This was reported on June 4 in the journal Science Daily.
Comet 3I/ATLAS is the third confirmed interstellar object recorded in the Solar System. Unlike the previous two, it was discovered early enough for detailed observation.
The team registered the first signs of gas emission from the MDM observatory in Arizona. Then the ALMA telescope complex in the Chilean Atacama desert was connected to the work, whose sensitivity made it possible to distinguish between ordinary water and water enriched with deuterium.
The observations were carried out using the MIRI (Mid-Infrared Instrument) instrument in two stages after the comet passed perihelion. The first series took place on December 15-16, when 3I/ATLAS was located about 329 million km from the Sun; the second — on December 27, at a distance of about 379 million km.
The main result was the first direct detection of methane on an interstellar visitor. Methane is an extremely volatile substance that easily changes from a solid state to a gas. The fact that it appeared only after the comet passed the point closest to the Sun indicates that the gas was hiding under the surface and came out only when the solar heating reached deeper ice layers. The ratio of methane to water turned out to be significantly higher than that of the vast majority of comets in the Solar system.
At the same time, observations confirmed another anomaly: the comet emits exceptionally large amounts of carbon dioxide relative to water — significantly more than typical solar comets. Taken together, the data on methane and co₂ indicate that 3I/ATLAS formed in a fundamentally different chemical environment before setting off on a journey through interstellar space.
The telescope also tracked how the comet's activity changed as it moved away from the Sun. Gas production declined sharply, with water showing the steepest drop. This is because water is less volatile than methane or Co₂, which means that its evaporation stops faster when the temperature decreases.
The MIRI integrated field spectrometer made it possible not only to identify gases around the core, but also to map their spatial distribution. The authors consider the data obtained as the first detailed chemical portrait of an object from another star system.
On March 9, a group of astronomers led by Nathan Roth, a specialist from the American University, found out that the interstellar comet 3I/ATLAS contains an unusual combination of molecules — methanol and hydrogen cyanide (HCN). Analysis of the data showed that the comet could have formed in conditions different from those in which comets usually occur in the Solar System.
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