Billions of years ago in a nascent planetary system somewhere in the Milky Way galaxy, the icy fragment now known as 3I/ATLAS was getting knocked around as larger planets formed. Powerful gravitational interactions eventually catapulted it out of the system, and it began a journey through our Milky Way galaxy.

In July 2025, the comet was only the third interstellar object ever detected passing through our solar system – the meaning of the ‘3I’ in its name. Objects like 3I/ATLAS offer the unparalleled opportunity for up-close study of something from very far away. Astronomers used the NIRSpec (Near-Infrared Spectrograph) instrument on NASA’s James Webb Space Telescope to discover surprising details of 3I/ATLAS’s chemical makeup, with ratios of heavy carbon and heavy hydrogen never seen among comets in our solar system. Future study of interstellar objects will build on these findings toward a better understanding of how our solar system fits into the larger picture of our galaxy.