{
  "abstract": "Recent JWST observations have revealed unusually high $^{12}$C/$^{13}$C ratios in carbon-bearing molecules of the interstellar object 3I/ATLAS, consistent with formation in a lower-metallicity environment than the present-day local interstellar medium (ISM). 3I/ATLAS also exhibits an exceptionally high water D/H ratio, exceeding those in Solar System comets and nearby low-mass star-forming regions. Here we investigate whether this high water D/H ratio can be reproduced in a low-metallicity formation scenario, using gas-ice astrochemical models. Assuming that the water observed in 3I/ATLAS was inherited from the parent molecular cloud and core, we perform a grid of astrochemical models covering the cloud to core stages, varying the gas density, ultraviolet radiation field ($χ$), cosmic-ray ionization rate ($ζ$), and metallicity, while solving thermal balance for the gas temperature. We find that lower metallicity enhances H$_3^+$ deuteration and, more importantly, its transfer to water ice. In contrast, water D/H ratio depends non-monotonically on $χ$ and $ζ$, because of competing chemical and thermal effects. In our models, the observed water D/H ratio is most readily reproduced at subsolar metallicities, $\\lesssim0.5Z_\\odot$, and relatively high cloud densities of $\\sim$10$^4$ cm$^{-3}$ without strong constraints on either $χ$ or $ζ$, as long as $ζ<10^{-15}$ s$^{-1}$. The D/H ratio of methane normalized by that of water is not sensitive to the metallicity, being consistent with the similar values observed in 67P/Churyumov-Gerasimenko and 3I/ATLAS. These results suggest that water deuteration may provide a complementary probe of the metallicity and physical condition of the parent molecular cloud and dense core of interstellar objects.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.12370",
  "author_total": 8,
  "authors": [
    {
      "name": "Kenji Furuya"
    },
    {
      "name": "Martin Cordiner"
    },
    {
      "name": "Dominique Bockelée-Morvan"
    },
    {
      "name": "Dennis Bodewits"
    },
    {
      "name": "Colin Orion Chandler"
    },
    {
      "name": "Maria N. Drozdovskaya"
    },
    {
      "name": "Nathan X. Roth"
    },
    {
      "name": "Geronimo Villanueva"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/egsrszw1e21qb.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.12370",
  "fulltext_url": null,
  "id": "egsrszw1e21qb",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.12370",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "arxiv",
      "astro-ph.GA"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.12370",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-14",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/egsrszw1e21qb.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.12370",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.12370"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "High water D/H ratio of the interstellar object 3I/ATLAS is consistent with a low-metallicity origin",
  "title_text": "High water D/H ratio of the interstellar object 3I/ATLAS is consistent with a low-metallicity origin",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/egsrszw1e21qb",
  "venue": "arXiv",
  "versions": []
}