Discovered just a year ago, interstellar comet 3I/ATLAS could be one of the oldest objects ever observed by humanity

An interstellar comet discovered just over a year ago may be one of the oldest objects ever observed by humanity, with new research suggesting it could have formed between 10 billion and 12 billion years ago, making it nearly as old as the Milky Way and not far behind the age of the universe itself.

Comet 3I/ATLAS first captured astronomers' attention after it was identified speeding through the solar system from beyond its boundaries. Initially discovered on July 1, 2025, by NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescopes, the object quickly became a scientific curiosity and the third known interstellar visitor ever detected, following 1I/'Oumuamua in 2017 and 2I/Borisov in 2019.

How old is Interstellar comet 3I/ATLAS?

Preliminary findings from a study posted on the preprint server Research Square suggest that 3I/ATLAS may have formed in a cold and distant region of the Milky Way around 10 billion to 12 billion years ago. If confirmed, the comet would be more than twice as old as Earth and the solar system, which are approximately 4.5 billion and 4.6 billion years old, respectively.

At the upper end of those estimates, the comet's age would place it remarkably close to that of the Milky Way galaxy, estimated at about 13.6 billion years, and the universe, which is roughly 13.8 billion years old.

But could 3I/ATLAS be that old?

However, the object's age remains uncertain. According to an analysis by researchers at the University of Oxford, 3I/ATLAS may be significantly younger than the upper estimate while still predating the solar system. Using what researchers call the Ōtautahi-Oxford Model, a statistical framework designed to estimate the origins and ages of interstellar objects based on their trajectories, the team concluded that the comet has roughly a two-thirds probability of being older than the solar system.

Their best estimate places the object's age at around 7 billion years.

Secret behind Interstellar comet 3I/ATLAS’s ancient age

Researchers believe the comet's extraordinary age may be linked to its place of origin.

Unlike previous interstellar visitors, 3I/ATLAS appears to be traveling along a steep trajectory through the galaxy, leading scientists to suspect that it originated in the Milky Way's "thick disk" a region populated by some of the galaxy's oldest stars.

The thick disk surrounds the younger thin disk, which contains the Sun and the solar system. "This is an object from a part of the galaxy we've never seen up close before," University of Oxford astrophysicist Chris Lintott told Space.com. "We think there's a two-thirds chance this comet is older than the solar system, and that it's been drifting through interstellar space ever since."

If the comet indeed formed around one of the Milky Way's ancient stars, researchers say it could contain large amounts of water ice and preserve clues about conditions in the early galaxy.

Discovery and early observations

The first observations of 3I/ATLAS were reported to the Minor Planet Center on July 1, 2025, by the ATLAS telescope in Rio Hurtado, Chile. Astronomers later identified earlier images of the object in archived observations from three ATLAS telescopes and Caltech's Zwicky Transient Facility at Palomar Observatory in California. These pre-discovery observations extended the comet's documented history back to June 14, 2025.

Soon after its discovery, online speculation suggested the object might be an alien spacecraft. However, astronomers overwhelmingly concluded that 3I/ATLAS is a natural interstellar comet originating from an as-yet unidentified star system.