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Updated: Jun 24, 2026

Atom Probe Tomography Analysis of Exsolved Mineral Phases
Published on: October 25, 2019
Isotopic evidence for a cold and distant origin of 3I/ATLAS
Martin Cordiner1,2, Nathan X Roth3,4, Marco Micheli5
1Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA. martin.cordiner@nasa.gov.
None:
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 formation1-3. 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, and 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.
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