NASA’s Webb Finds Clues to Ancient, Distant Origin of Comet 3I/ATLAS

As interstellar comet 3I/ATLAS began moving away from the Sun in December 2025, astronomers took the opportunity to turn NASA’s powerful James Webb Space Telescope in its direction and capture detailed measurements of its chemical components. The comet was freshly warmed from its closest pass by the Sun, and its ancient ice had been converted to a bright coma of gas ideal for observation. Webb captured detailed data, including chemical ratios of carbon and deuterium, also known as heavy hydrogen, that are not found in solar system comets. The results surprised researchers. Working backward, astronomers used the components that make up comet 3I/ATLAS to understand the environment in which it formed. A paper detailing the findings published June 22 in the journal Nature . Researchers used the NIRSpec (Near-Infrared Spectrograph) instrument on NASA’s James Webb Space Telescope to map specific chemical contents of comet 3I/ATLAS as it moved away from the Sun. Image: NASA, ESA, CSA, STScI, Martin Cordiner (CUA, NASA-GSFC); Image Processing: Alyssa Pagan (STScI) The comet’s name comes from its status as the third confirmed interstellar comet, meaning it originated outside the solar system, and the telescope that first spotted it, the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System). …