Observations by the James Webb Space Telescope have provided new clues about the possible origin of interstellar comet 3I/Atlas. A research team led by Nathan Roth of American University found that the comet’s Methane contains an unusually high proportion of deuterium, a heavier form of hydrogen.

With support from NASA’s Goddard Space Flight Center, the researchers measured the ratio of deuterium to ordinary hydrogen in the comet. At around 3.2 percent, the ratio in its methane was approximately 13 times higher than the value measured in comet 67P/Churyumov-Gerasimenko, which likely originated in our Solar System.

Webb observed 3I/Atlas on December 22 and 23, 2025, when the comet was about 2.4 times farther from the Sun than Earth. The telescope analyzed infrared light from the Coma, the cloud of gas surrounding the comet’s icy nucleus. Deuterium can replace ordinary hydrogen in methane, altering the molecule’s infrared signature and allowing astronomers to distinguish between the two forms.

The measured ratio is the highest ever recorded for methane in the Solar System, according to the study’s authors. The comparison with 67P is particularly useful because it is the only other comet in which deuterium-bearing methane has been detected.

The deuterium-to-hydrogen ratio in 3I/Atlas’s methane was also about three times higher than the ratio previously measured in the comet’s water. The researchers suggest that the methane may have formed later, after chemical processes had more time to enrich the surrounding material with deuterium.

The findings are consistent with a scenario in which 3I/Atlas formed inside a cold cloud or near a young star. The proposed environment would have contained relatively few elements heavier than helium and would have been exposed to intense cosmic radiation. These high-energy particles can trigger chemical reactions that increase the amount of deuterium in molecules.

However, the observations do not identify a definitive birthplace for 3I/Atlas. They instead offer a plausible formation scenario and a rare opportunity to study the early chemistry of a planetary system beyond our own. The results were published in Nature Astronomy.

Sources: t3n.