As interstellar comet 3I/ATLAS moved away from the Sun in December 2025, NASA’s James Webb Space Telescope (JWST) turned its powerful instruments toward the icy visitor. The observations, taken shortly after the comet's closest solar pass, allowed astronomers to analyze its chemical makeup while the object's ancient ices were still warmed and actively outgassing.
The Webb telescope detected a suite of chemical compounds in the comet's coma, including carbon monoxide, carbon dioxide, and organic molecules. These signatures provide a fingerprint of the material from which the comet formed, likely in a distant, cold region of its parent star system. The data represent one of the most detailed chemical analyses of an interstellar object ever obtained.
The comet, designated 3I/ATLAS, was discovered earlier in 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS). It entered the inner solar system on a hyperbolic trajectory, confirming its origin outside our solar system. Its perihelion occurred in late 2025, after which it began its long journey back toward interstellar space.
This study sheds light on the composition of primordial material from another star system, offering a rare window into the chemistry of exoplanetary building blocks. Since interstellar objects are thought to be ejected from their home systems during planetary formation, each new detection helps refine models of how planets and their chemical reservoirs evolve across the galaxy.
However, the comet is now fading rapidly as it recedes from the Sun, limiting the window for further detailed measurements. Future interstellar visitors may provide additional context, but each event is unpredictable and rare, making every observation precious.