New Delhi: NASA’s James Webb Space Telescope has detected methane gas on an interstellar object for the first time, revealing that the visitor from the mid-disk
of the Milky Way, 3I/Atlas possesses a chemical composition drastically different from comets native to our Solar System. Researchers used the Mid-Infrared Instrument (MIRI) on Webb to observe the comet on two separate dates as it travelled away from the Sun after the perihelion, or closest approach to Sun in October last year. The first observations with Webb were between 15 and 16 December, when the comet was about 329 kilometres from the Sun, followed by a second observation on 27 December, when the object was at a distance of 379 kilometres.
The observations revealed a surprisingly high abundance of methane relative to water, a ratio with very few analogues in our Solar System. As methane is highly volatile and sublimates easily from solid ice into gas, its delayed appearance indicates that it outgassed from deep within the interior of the comet. This subsurface location of the methane protected the ice until the heat from the Sun during the close approach penetrated the icy depths of the comet. The observations also confirmed that 3I/Atlas is unusually rich in carbon dioxide, releasing far more carbon dioxide relative to water than typical Solar System comets.
Chemical fingerprint of the Origin System
The observations of the high levels of methane and carbon dioxide indicate that 3I/Atlas formed in an environment with a chemical setting very different from the Solar System. As the comet moved away from the Sun, Webb tracked a sharp decline in the overall gas production, with water exhibiting the most pronounced drop. Water is less volatile than methane or carbon dioxide, and its vapourisation reduces more rapidly as solar heating decreases, and the surface of the comet cools. A paper describing the research has been published in The Astrophysical Journal Letters.
