NASA's James Webb Space Telescope has made the first direct detection of methane on an interstellar comet. The findings reveal unusual chemistry in comet 3I/ATLAS, including high levels of carbon dioxide.
The observations used the telescope's Mid-Infrared Instrument during sessions on December 15 and 16, when the comet was 205 million miles from the Sun, and again on December 27 at 236 million miles away. Researchers identified methane gas that likely emerged after solar heating reached deeper layers of ice. The ratio of methane to water was much higher than in most solar system comets. Carbon dioxide levels were also exceptionally high relative to water, pointing to a different formation environment. Gas production declined sharply as the comet moved farther from the Sun, with water showing the steepest drop. The results were published in The Astrophysical Journal Letters.