Isotopic Evidence for a Cold and Distant Origin of Interstellar Object 3I/Atlas

[2603.06911] Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS Support arXiv on Cornell Giving Day! We're celebrating 35 years of open science - with YOUR support! Your generosity has helped arXiv thrive for three and a half decades. Give today to help keep science open for ALL for many years to come. Donate! --> Astrophysics > Earth and Planetary Astrophysics arXiv:2603.06911 (astro-ph) [Submitted on 6 Mar 2026] Title: Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS Authors: Martin Cordiner , Nathan X. Roth , Marco Micheli , Geronimo Villanueva , Davide Farnocchia , Steven Charnley , Nicolas Biver , Dominique Bockelee-Morvan , Dennis Bodewits , Colin Orion Chandler , Jacques Crovisier , Maria N. Drozdovskaya , Kenji Furuya , Michael S. P. Kelley , Stefanie Milam , John W. Noonan , Cyrielle Opitom , Megan E. Schwamb , Cristina A. Thomas View a PDF of the paper titled Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS, by Martin Cordiner and 18 other authors View PDF HTML (experimental) Abstract: 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 = (0.95 +- 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 $\lesssim30$ K in a relatively metal-poor environment, early in the history of the Galaxy. When interpreted with respect to models for Galactic chemical evolution, the carbon isotopic composition implies that 3I/ATLAS accreted roughly 10-12 billion years ago, following an early period of intense star formation. 3I/ATLAS thus represents a preserved fragment of an ancient planetary system, and provides direct evidence for active ice chemistry and volatile-rich planetesimal formation in the young Milky Way. Comments: In Review at Nature; March 6th 2026 Subjects: Earth and Planetary Astrophysics (astro-ph.EP) ; Astrophysics of Galaxies (astro-ph.GA) Cite as: arXiv:2603.06911 [astro-ph.EP] (or arXiv:2603.06911v1 [astro-ph.EP] for this version) https://doi.org/10.48550/arXiv.2603.06911 Focus to learn more arXiv-issued DOI via DataCite Related DOI : https://doi.org/10.21203/rs.3.rs-8930056/v1 Focus to learn more DOI(s) linking to related resources Submission history From: Martin Cordiner PhD [ view email ] [v1] Fri, 6 Mar 2026 22:16:58 UTC (452 KB) Full-text links: Access Paper: View a PDF of the paper titled Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS, by Martin Cordiner and 18 other authors View PDF HTML (experimental) TeX Source view license Current browse context: astro-ph.EP < prev | next > new | recent | 2026-03 Change to browse by: astro-ph astro-ph.GA References & Citations NASA ADS Google Scholar Semantic Scholar export BibTeX citation Loading... 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