An interstellar comet that passed through the Solar System in late 2025 may be up to 12 billion years old, far older than the sun, according to a study published in the journal Nature on June 22. Researchers used the NASA/ESA/CSA James Webb Space Telescope to examine Comet 3I/ATLAS as it moved away from the sun, when heat transformed its ancient ice into a glowing gas cloud, enabling detailed chemical analysis.
Ancient origins during cosmic noon
The findings suggest the comet originated in a distant planetary system during the Universe's 'cosmic noon', a period when star formation across the galaxy was at its peak. The comet is estimated to have formed between 10 and 12 billion years ago, significantly older than the sun, which is around 4.5 billion years old. Comet 3I/ATLAS is only the third confirmed interstellar comet ever detected, named after its status as the third known visitor from beyond the Solar System and the NASA-funded ATLAS telescope that first spotted it.
Unique chemical signatures
Using Webb's Near-Infrared Spectrograph (NIRSpec), scientists measured chemical signatures unlike those seen in any known Solar System comet. A key discovery was an exceptionally high concentration of deuterium, a heavier form of hydrogen, at levels around 30 times greater than those found in Solar System comets. This points to the comet having formed in an extremely cold environment early in the Milky Way's history, with its material remaining deeply frozen for billions of years.
The telescope also detected only trace amounts of carbon-13 compared with the lighter carbon-12 isotope. Since galaxies become enriched with carbon-13 as successive generations of stars live and die, the low levels provide further evidence of the comet's ancient origins.
Scientific collaboration and implications
'This was a unique opportunity to study an ancient object from the distant Galaxy, probably pre-dating our sun and Solar System,' said astro-chemist Martin Cordiner of NASA's Goddard Space Flight Center, lead author of the study. 'On the one hand, we get direct insight into that distant time and place, and on the other, we learn something about how unusual our own Solar System may be.'
Astronomers from multiple disciplines collaborated to observe the comet during its brief journey, securing permission to interrupt Webb's planned observing schedule. A separate study led by Cyrielle Opitom of the University of Edinburgh, using the European Southern Observatory's Very Large Telescope, examined the comet's chemical makeup, focusing on forms of carbon and nitrogen contained in cyanide.
Broader questions about life's origins
Scientists believe such observations could help answer broader questions about the origins of life in the Universe. 'For us as scientists, finding these rare isotopes is fascinating, but the bigger picture here is looking at the possibilities of prebiotic chemistry elsewhere in the galaxy,' said Stefanie Milam of NASA Goddard, a co-author of the study. 'So far, we know of only one place in the vast cosmos where chemical ingredients led to life – our Solar System, our Earth. Analysis of these interstellar objects is a major step towards learning how common, or uncommon, the conditions for the evolution of life are in the Universe.'
