Interstellar Comet 3I/Atlas Is Older Than Our Sun

The analyses also show that 3I/Atlas exhibits different isotope ratios than comets in our solar system, particularly in the elements carbon and nitrogen. "Im Gegensatz zu Kometen unseres Sonnensystems enthält dieser interstellare Besucher ungewöhnlich wenig Isotope mit hohem Gewicht," reports Aravind Krishnakumar from the University of Liège in Belgium.

Unusual Isotopes in Comparison

The researchers explain this with the history of the universe: At the Big Bang 13.8 billion years ago, only the light elements hydrogen, helium, and a little lithium were initially produced. Heavy elements such as carbon and nitrogen formed later inside stars and were released into space through supernova explosions. A very old comet should therefore contain fewer heavy isotopes than a comparatively young celestial body.

"3l/Atlas bietet uns die aufregende Möglichkeit, die Zusammensetzung eines anderen Planetensystems zu untersuchen," explains Rosemary Dorsay from the University of Helsinki, "und zwar eines, das sich lange vor unserer Sonne und unserem Sonnensystem gebildet hat". The comet must therefore have formed in the vicinity of a young star of an earlier generation, the scientists write in the journals "Nature Astronomy" and "Nature".

Significance for Astronomy

The new findings are based on measurements from various telescopes, including images from the Hubble Space Telescope. An image from 21 July 2025 shows the comet at a distance of 277 million miles from Earth. At that time, the object was also described as particularly active, as it was ejecting gas and dust into space.

For astronomy, 3I/Atlas is a rare stroke of luck: such interstellar visitors are only within reach of Earth-based telescopes for a short time. Researchers hope that detailed chemical analysis will provide new clues about the conditions under which planetary systems formed in the first billions of years of the universe.

According to the team's assessment, the discovery shows that comets can function as a kind of cosmic witnesses of past stellar generations. By preserving the isotopes in their ice, they carry information about the environment of their home stars with them across billions of years.

Future observations are intended to clarify how typical the composition of 3I/Atlas is for interstellar objects. Since only three such visitors are known so far, the data basis is still very small. Every further discovery of an interstellar comet could supplement the picture that researchers are currently drawing of the chemical development of early planetary systems.