• The team, led by Xabier Pérez Couto from the CITIC at the University of A Coruña, reveals the trajectory the celestial object has followed through the Milky Way.
• It is the third interstellar object ever detected — a body travelling from another stellar system which, although expected to be relatively common, had only been observed twice before.
• Using data from the European Space Agency’s Gaia mission — coordinated in Galicia by CITIC researcher Minia Manteiga — the team calculated not only the comet’s orbit but also the orbits of more than 13 million stars.

A Coruña, 22 September 2025.– A research team led by Xabier Pérez Couto, from the Centre for Research in Information and Communication Technologies (CITIC) at the University of A Coruña, has traced the orbital history of the third interstellar object ever detected in our Solar System: 3I/ATLAS. The study, available on the open-access repository arXiv and submitted for publication in The Astrophysical Journal, reveals the path this comet has followed through the Milky Way over the past 10 million years.

3I/ATLAS was discovered on 1 July by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey in Chile. It is the third known interstellar object, following 1I/‘Oumuamua (2017) and 2I/Borisov (2019).

“What makes 3I/ATLAS unique is that it allows us to study the evolution of objects originating from other stellar systems — something we had only theorised about until now. Each observation is like opening a window into the Universe’s past,” explains Pérez Couto, CITIC researcher and team leader.

Notable features of the comet include its intense activity — indicating a significant presence of ice — and its high velocity of around 58 km/s (over 200,000 km/h), making it a fast-moving but extremely valuable visitor for research.

Using high-precision data from the European Space Agency’s Gaia mission, the research team calculated both the orbit of 3I/ATLAS and those of more than 13 million stars, with the aim of identifying potential close encounters between them and the comet. A total of 93 possible interactions were found, 62 of them with a high degree of confidence. However, due to the comet’s high velocity, the researchers determined that none of these stars were able to significantly alter its trajectory.

A 10-Billion-Year-Old Time Capsule

The findings suggest that 3I/ATLAS is an extraordinarily ancient object, with an estimated age of around 10 billion years. This makes it a true cosmic time capsule, preserving information about the formation and evolution of the earliest planetary systems in the Universe. Although its parent star has not been identified — and likely never will be — the data indicate that it originates from the same dynamic environment as much of the material in the Milky Way’s thin disk.

The study underscores the challenge of tracing the origins of individual interstellar objects. Nevertheless, the team highlights that as more of these objects are discovered, it will become possible to identify chemical and dynamical trends on a galactic scale, offering unique insights into how planets and comets form and disperse throughout the cosmos.