Scientists have taken a closer look at 3I/ATLAS, a fast-moving interstellar comet that passed through our Solar System and is now continuing its journey back into deep space. First identified on July 1, 2025 by the ATLAS survey in Chile, it is only the third interstellar object ever recorded.
New observations published in Nature by a team led by Martin Cordiner of NASA Goddard Space Flight Center suggest that 3I/ATLAS is far older than the Sun. By combining data from the James Webb Space Telescope and the Atacama Compact Array, researchers analyzed the gases released as the comet warmed near the Sun.
The key clue came from its carbon chemistry. The comet showed a notably low amount of carbon-13 compared with similar Solar System objects. That pattern points to an origin in the early Milky Way, when the balance of carbon isotopes was different. The study estimates that 3I/ATLAS may have formed around 12 billion years ago, making it a true relic from the galaxy's early era.
Its speed also stood out. At its closest approach to the Sun, the comet was traveling at more than 68 kilometers per second, reinforcing the idea that it arrived from another star system. Scientists believe it may have been ejected long ago from an ancient stellar region of the Milky Way known as the thick disk.
Interstellar visitors like 3I/ATLAS help astronomers understand how planetary systems form, evolve, and sometimes scatter material into the space between stars. With the upcoming Vera Rubin Observatory, researchers expect to detect many more such objects, turning rare discoveries into a broader cosmic dataset. This could open a new window on the history of star and planet formation across the galaxy.