Interstellar comet may be oldest object seen in our solar system, scientists say

[muriel_volestrangler]

An interstellar comet that blazed past the sun last year could be nearly three times older than our solar system and is unlike anything ever before seen in our cosmic back yard, astronomers said on Monday.

The comet 3I/Atlas is just the third visitor from beyond our solar system that humanity has ever observed, its unusual brightness offering scientists an unprecedented opportunity to study something that came from elsewhere in the galaxy.
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According to a study published in the journal Nature, 3I/Atlas could be up to 12bn years old. Our solar system is believed to have formed about 4.5bn years ago.

The lead study author, Martin Cordiner of Nasa’s Goddard Space Flight Center, told Agence France-Presse that “maybe it’s the oldest object to have been observed in our solar system”. However, there could be “edge-case scenarios” that offer other explanations for the comet’s unusual chemical composition, he added.

https://www.theguardian.com/science/2026/jun/22/interstellar-comet-may-be-oldest-object-seen-in-our-solar-system-research-finds

Interstellar objects provide the only directly observable samples of icy planetesimals formed around other stars, and can therefore provide insight into the diversity of physical and chemical conditions occurring during exoplanet formation. Here we report isotopic measurements of the interstellar comet 3I/ATLAS, which reveal an elemental composition unlike any Solar System body. The water in 3I/ATLAS is enriched in deuterium, at a level of D/H = (0.98 ± 0.06)%, which is more than an order of magnitude higher than in known comets, while its range of 12C/13C ratios (141–191 for CO2 and 123–172 for CO) exceeds typical values found in the Solar System, as well as nearby interstellar clouds and protoplanetary disks. Such extreme isotopic signatures indicate formation at temperatures ≲ 30 K in a relatively metal-poor environment. When interpreted with respect to models for Galactic chemical evolution, the carbon isotopic composition implies that 3I/ATLAS may have accreted as long ago as 12 billion years, following a period of intense, early star formation. 3I/ATLAS thus represents a preserved fragment of an ancient planetary system.

https://www.nature.com/articles/s41586-026-10771-6