{
  "abstract": "We present JWST/NIRSpec PRISM observations of the interstellar comet 3I/ATLAS obtained on 2025 August 6 (Epoch 1), 2025 December 22 (Epoch 2), and 2026 April 1 (Epoch 3), spanning 8 months around perihelion at heliocentric distances of 3.3, 2.4, and 5.7 au, respectively. The spectra reveal a broad 3 μ m absorption band together with H ₂ O, CO ₂ , and CO gas emission. Unlike previously reported water-ice-rich solar system comae, the strong 3 μ m absorption is accompanied by weak or absent 1.5 and 2.0 μ m water-ice bands. Spectral modeling indicates that the observations are best reproduced by submicron- to micron-sized water-ice-bearing aggregates containing refractory material. Compared with Epoch 1, the Epoch 3 spectrum favors the presence of a second population of larger, micron-sized, ice-rich aggregates and exhibits a subtle Fresnel-like structure near 3.1 μ m, consistent with crystalline water ice. The observations can be explained by either crystalline water ice at both epochs, with the spectral evolution arising primarily from changes in grain size and refractory mixing, or an evolution from an amorphous-like to crystalline state. The spectral properties of 3I bridge those of water-ice-bearing solar system comae and several spectral classes of mid-sized trans-Neptunian objects. These similarities suggest that the icy building blocks of planetesimals formed in different protoplanetary disks may share a common continuum in the physical state of water ice, ranging from pure ice grains to water-ice-bearing aggregates with varying refractory content at submicron-to-micron scales, with the grains observed in 3I lying toward the refractory-rich end of this continuum.",
  "abstract_shown": true,
  "affiliations": [
    "Southwest Research Institute",
    "University of Maryland",
    "NASA Goddard Space Flight Center",
    "Catholic University of America",
    "Auburn University",
    "Universität Bern",
    "American University",
    "California Institute of Technology",
    "Université Lyon 1",
    "ESA NEO Coordination Centre",
    "Queen’s University Belfast",
    "Michigan State University"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 15,
  "authors": [
    {
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        0
      ],
      "name": "Silvia Protopapa",
      "orcid": "0000-0001-8541-8550"
    },
    {
      "affs": [
        1
      ],
      "name": "Michael S. P. Kelley",
      "orcid": "0000-0002-6702-7676"
    },
    {
      "affs": [
        2,
        3
      ],
      "name": "Martin A. Cordiner",
      "orcid": "0000-0001-8233-2436"
    },
    {
      "affs": [
        2
      ],
      "name": "Stefanie N. Milam",
      "orcid": "0000-0001-7694-4129"
    },
    {
      "affs": [
        4
      ],
      "name": "Dennis Bodewits",
      "orcid": "0000-0002-2668-7248"
    },
    {
      "affs": [
        2
      ],
      "name": "Steven B. Charnley",
      "orcid": "0000-0001-6752-5109"
    },
    {
      "affs": [
        5
      ],
      "name": "Maria N. Drozdovskaya",
      "orcid": "0000-0001-7479-4948"
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    {
      "affs": [
        2,
        6
      ],
      "name": "Sara Faggi",
      "orcid": "0000-0003-0194-5615"
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    {
      "affs": [
        7
      ],
      "name": "Davide Farnocchia",
      "orcid": "0000-0003-0774-884X"
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    {
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        8
      ],
      "name": "Aurélie Guilbert-Lepoutre",
      "orcid": "0000-0003-2354-0766"
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    {
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        9
      ],
      "name": "Marco Micheli",
      "orcid": "0000-0001-7895-8209"
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    {
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        2,
        6
      ],
      "name": "Nathan X. Roth",
      "orcid": "0000-0002-6006-9574"
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    {
      "affs": [
        10
      ],
      "name": "Megan E. Schwamb",
      "orcid": "0000-0003-4365-1455"
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    {
      "affs": [
        11
      ],
      "name": "Darryl Z. Seligman",
      "orcid": "0000-0002-0726-6480"
    },
    {
      "affs": [
        2
      ],
      "name": "Geronimo L. Villanueva",
      "orcid": "0000-0002-2662-5776"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9kazt2s38d3nn.bib",
  "cited_by": 0,
  "doi": "10.3847/2041-8213/aea60d",
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  "id": "9kazt2s38d3nn",
  "issns": [
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  "language": null,
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  "licence_label": "CC BY 4.0",
  "licence_source": "article",
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  "native_subjects": [
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      "openalex",
      "3103|Astro and Planetary Science"
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aea60d/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-26",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/9kazt2s38d3nn.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:13Z",
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  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Astro and Planetary Science",
      "subfield": "planetary"
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  ],
  "title": "JWST Reveals Refractory-rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks",
  "title_text": "JWST Reveals Refractory-rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:13Z",
  "url": "https://research.draconitic.com/paper/9kazt2s38d3nn",
  "venue": "The Astrophysical Journal Letters",
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    {
      "doi": "10.48550/arxiv.2609.19286",
      "pid": "2ka0gzkbspk23",
      "relation": "preprint",
      "title": "JWST Reveals Refractory-Rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks",
      "venue": "arXiv"
    }
  ]
}