Nitrogen-rich gas tail shows interstellar comet 3I/ATLAS formed in extreme cold

By the Everything Space news desk · 08 Sep 2026 · written from the sources below

Spectroscopic observations reveal 3I/ATLAS likely formed at temperatures below -240°C, offering rare insight into the chemistry of another planetary system.

Astronomers studying interstellar comet 3I/ATLAS have found further evidence that it formed in an extraordinarily cold environment, far from the star it once orbited.

Using the William Herschel Telescope's WEAVE spectrograph, a research team led by Lea Ferellec of Northumbria University examined the comet's plasma tail as it moved away from the Sun. They detected five different ionized gases in the tail at once, a rare feat even for comets within our own Solar System and unprecedented for an object from outside it.

Among these gases, the team measured unusually high levels of ionized molecular nitrogen relative to ionized carbon monoxide. Because nitrogen retention in cometary ice is highly sensitive to formation temperature, this ratio implies that 3I/ATLAS coalesced at temperatures below roughly 33 kelvin, equivalent to about -240°C, indicating it formed in a very distant, frigid region of its parent planetary system.

The findings reinforce previous studies of the comet that also suggested an extremely cold origin, giving scientists multiple independent lines of evidence pointing to the same conclusion.

The researchers also tracked how the various ions evolved with distance along the comet's tail, marking the first time such detailed ion-by-ion analysis has been carried out for an object originating outside the Solar System.

3I/ATLAS, discovered in July 2025, is only the third confirmed interstellar object detected passing through the Solar System, after 'Oumuamua in 2017 and Borisov in 2019. Because such objects carry material formed around other stars, studying their composition allows scientists to compare the ingredients of distant planetary systems with our own.

The study has been published in Monthly Notices of the Royal Astronomical Society.

Written in Everything Space’s own words by our news-desk model from the sources above, and checked against them in code: every number in this report appears in its sources, and no sentence is copied from them.