Evidence Mounts: This Interstellar Visitor Is Even Older and Stranger Than We Thought
By Joseph Howlett edited by Claire Cameron
Image of interstellar comet 3I/ATLAS taken by NASA’s Hubble Space Telescope on July 21, 2025.
NASA/ESA/David Jewitt
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The last interstellar visitor discovered in our solar system was born somewhere in the universe that looked nothing like our home and, according to a new study, long before the solar system even formed – in the infancy of the cosmos.
Spotted in 20253I/ATLAS is the third interstellar comet identified by astronomers fly through our solar system, after 1I/ʻOumuamua and 2I/Borisov. Since then, researchers have used the James Webb Space Telescope (JWST) and the ground-based Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to study study the gas coming out of 3I/ATLAS as the heat of the sun burned its icy insides. The chemical isotopes contained in the gas reveal details of the comet’s murky history-and a new study published in Nature (after it was posted online in preprint in March) helps give more color to this origin story.
Using carbon isotopes present in the comet to estimate its age, the authors believe it could be even older than previous estimates had suggested – up to 12 billion years old. That’s much older than our own solar system, which is 4.5 billion years old, and just under two billion years younger than the universe itself.
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The study also shows that 3I/ATLAS came from a much colder region of its own solar system than any of the comets we see in ours. The comet contains far more heavy hydrogen – in the form of an isotope called deuterium, which has one neutron and one proton – than any local space rock, a quality that tends to indicate a colder environment. This finding is consistent with other recent research, and astronomers are increasingly speculating that our solar system may be a strange phenomenon and that the comets we have studied for centuries are different from most comets in the universe.
It was thanks to cutting-edge telescopes like ALMA and JWST that we spotted these first three interstellar objects. And with the Vera C. Rubin Observatory in Chile now beginning a decade-long survey of the sky, more such discoveries are likely to follow, says Cyrielle Opitom, an astronomer at the University of Edinburgh in Scotland and co-author of the new study. “We hope they will be as exciting as 3I/ATLAS,” she says. These wandering rocks could soon tell us much more about what lies beneath. the ends of the universe– and maybe how weird we really are.
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