Mystery interstellar object could be the oldest known comet

Georgina Rannard

Science and climate correspondent

ESO’s Very Large Telescope (VLT) has obtained new images of the path, shown as a dotted line of lights, of 3I/Atlas, an interstellar object discovered last week

ESO/O. Hainaut ESO’s Very Large Telescope (VLT) has obtained new images of 3I/ATLAS, an interstellar object discovered last week. — ESO’s Very Large Telescope (VLT) has obtained new images of the path, shown as a dotted line of lights, of 3I/Atlas, an interstellar object discovered last week

A mystery interstellar object spotted last week by astronomers could be the oldest comet ever seen, according to scientists.

Named 3I/Atlas, it may be three billion years older than our own solar system, suggests the team from Oxford university.

It is only the third time we have detected an object that has come from beyond our solar system.

The preliminary findings were presented on Friday at the national meeting of the UK’s Royal Astronomical Society in Durham.

“We’re all very excited by 3I/Atlas,” University of Oxford astronomer Matthew Hopkins told BBC News.

“I’ve just finished my PhD where I spent four years predicting the discovery of [more] interstellar objects, and then for the first time in my studies, we found one,” he said.

Based on the object’s speed, Mr Hopkins says it could be more than seven billion years old, and it may be the most remarkable interstellar visitor yet.

3I/Atlas was first spotted on 1 July 2025 by the Atlas survey telescope in Chile, when it was about 670 million km from the Sun.

It is currently visible only with very large telescopes, and it is about the distance of Jupiter from Earth.

Since then astronomers around the world have been racing to identify its path and discover more details about it.

Mr Hopkins believes it originated in the Milky Way’s “thick disk”. This is a group of ancient stars that orbit above and below the area where the Sun and most stars are located.

The top view of the Milky Way, below, gives a sense of the object’s path around our galaxy. The estimated orbits of 3I/Atlas are in red and those of our Sun are in yellow.

The estimated orbits around the Milk Way of the object, in red, and our Sun, in yellow

Matthew Hopkins An artists's impression of the swirling white galaxy from above with concentric circles in yellow showing the sun's orbit and red showing the comet's orbit. — The estimated orbits around the Milk Way of the object, in red, and our Sun, in yellow

The team believe that because 3I/Atlas probably formed around an old star, it is made up of a lot of water ice.

That means that as it approaches the Sun later this year, the energy from the Sun will heat the object’s surface, leading to blazes of vapour and dust.

That could create a glowing tail.

The researchers made their findings using a model developed by Mr Hopkins.

“This is an object from a part of the galaxy we’ve never seen up close before,” said Prof Chris Lintott, co-author of the study.

“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.”

Interstellar objects form around other stars, at the start of those stars’ lives, explains Mr Hopkins.

“This connection back to their parent stars means that we can look at the stellar population of the Milky Way,” he adds.

Later this year, 3I/Atlas should be visible from Earth using amateur telescopes.

Before 3I/Atlas soared into view, just two others had been seen. One was called 1I/’Oumuamua, found in 2017 and another called 2I/Borisov, discovered in 2019.

Astronomers globally are currently gearing up to start using a new, very powerful telescope in Chile, called the Vera C Rubin.

When it starts fully surveying the southern night sky later this year, scientists expect that it could discover between five and 50 new interstellar objects.