UK astronomers find: Interstellar comet 3I/ATLAS formed in extreme cold

UK astronomers have uncovered new clues about the origins of 3I/ATLAS, only the third confirmed interstellar object ever detected, finding that the comet likely formed in an exceptionally cold environment far from its parent star.

The findings, published in Monthly Notices of the Royal Astronomical Society, are based on observations of ionised gases streaming from 3I/ATLAS as it moved away from the Sun. The study was led by Dr. Lea Ferellec, a research fellow at Northumbria University's School of Engineering, Physics and Mathematics, Phys.org writes. 

Researchers used the Large Integral Field Unit (LIFU) mode of WEAVE, a new instrument installed on the 4.2-meter William Herschel Telescope in the Canary Islands. Combining LIFU imaging spectroscopy with the telescope's non-sidereal guiding capabilities, the team detected five different ions in the comet's stream simultaneously.

The observation provides an unusually detailed look at the chemical composition of an object that originated outside the Solar System.

By comparing the amount of dinitrogen gas with carbon monoxide in 3I/ATLAS, the researchers estimated that the object formed at temperatures likely below -240°C (-400°F). Such conditions suggest that the comet developed in the distant, icy outer regions of its original planetary system, well away from its parent star.

Speaking about the findings, Ferellec said, "This object gives us a rare chance to study material that formed somewhere completely different from 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."

Interstellar objects are bodies that formed around stars other than the Sun before entering interstellar space and travelling potentially for millions of years. Only three have so far been identified, with 3I/ATLAS discovered in July 2025 as it passed through the inner Solar System before continuing back into deep space.

The researchers also examined how the ions changed as they travelled farther along the object's tail. The tail forms as plasma flowing from the Sun interacts with charged particles released by the comet. The observations provide the first detailed examination of these changes for an interstellar object of this type.

The study included researchers from the University of Edinburgh and highlights the capabilities of WEAVE-LIFU for investigating comets and other astronomical objects.

"Powerful, large-format IFUs with high sensitivity in the blue optical spectrum—like WEAVE-LIFU on the WHT—are opening new frontiers for the study of comets and other solar system objects," said ING Director Rubén Sánchez-Janssen.

"This discovery is a perfect example of the value of DDT, which is specifically designed to enable observations of exceptional and urgent scientific importance."

By Sabina Mammadli