Northumbria astronomer helps reveal secrets of rare interstellar visitor

A Northumbria University astronomer has helped uncover new clues about a rare icy object from outside our Solar System, revealing that it formed in extremely cold conditions, far away from any star.

Every so often, a large icy rock, similar to a comet, arrives from beyond our Solar System, having formed around a different star entirely then travelling for millions of years before reaching us.

These are called interstellar objects, and only three have ever been spotted. The most recent, known as 3I/ATLAS, was discovered in July 2025 as it sped past the Sun and back out into deep space.

Because these objects formed in a completely different part of the galaxy, studying them gives scientists a rare glimpse into how planets and comets form around other stars, not just our own.

Dr Lea Ferellec, a Research Fellow based in Northumbria's School of Engineering, Physics and Mathematics, led a study looking at the charged particles streaming off 3I/ATLAS as it moved away from the Sun.

Using WEAVE (the William Herschel Telescope Enhanced Area Velocity Explorer), a new-generation spectrograph on a powerful telescope in the Canary Islands, the team was able to identify five different charged molecules in this stream at once, something rarely achieved for a comet, let alone an object like this.

By measuring how much dinitrogen gas was present compared to carbon monoxide, the researchers worked out that 3I/ATLAS formed somewhere extremely cold, likely colder than -240°C.

This suggests it formed a long way from its home star, in the outer, icier edges of wherever its solar system took shape.

Speaking about the findings Dr Ferellec said: “This object gives us a rare chance to study material that formed somewhere completely different to our own Solar System.

“Finding that it's so rich in nitrogen tells us it likely formed in extremely cold conditions, far from its home star.

“Every one of these objects we study helps us understand a little more about how planets form around other stars."

The team also looked at how the charged gases changed the further they travelled along 3I/ATLAS's tail, which forms when plasma streaming from the Sun sweep the object's charged particles out behind it. This is the first time this level of detail has been captured for an object of this kind.

The research was carried out with colleagues at the University of Edinburgh. A paper entitled Ion abundances in the plasma tail of 3I/ATLAS show that it is N2-rich has been published in leading astronomy research journal Monthly Notices of the Royal Astronomical Society.