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    "story_id": "mp-2026-09-08-027",
    "source_story_id": "tmp-story-3iatlas-nitrogen-tail-front-rail",
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    "headline": "The Interstellar Comet's Tail Carried Unusual Nitrogen",
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    "dek": "Spectra of 3I/ATLAS detected five ions and set a lower limit on nitrogen-to-carbon monoxide above most Solar System comet values.",
    "summary": "Spectra of 3I/ATLAS detected five ions and set a lower limit on nitrogen-to-carbon monoxide above most Solar System comet values.",
    "body_text": "Post-perihelion observations with the William Herschel Telescope's WEAVE large integral-field unit detected N2+, CO+, CO2+, H2O+ and CH+ in the anti-solar plasma tail of 3I/ATLAS. Using fluorescence factors, the team derived a lower limit of 0.023 plus or minus 0.001 for N2/CO, describing the interstellar comet as nitrogen-rich relative to Solar System comets and consistent with cold formation conditions. The authors warn that ratios among the other ions cannot directly determine neutral abundances; a decrease in CH+ with distance was only marginal.",
    "why_it_matters": "Spectra of 3I/ATLAS detected five ions and set a lower limit on nitrogen-to-carbon monoxide above most Solar System comet values.",
    "limitations": [
      "The authors warn that ratios among the other ions cannot directly determine neutral abundances; a decrease in CH+ with distance was only marginal."
    ],
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    "first_published_at": "2026-09-08T09:00:00.000-04:00",
    "modified_at": "2026-09-08T09:00:00.000-04:00",
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        "text": "Spectra of 3I/ATLAS detected five ions and set a lower limit on nitrogen-to-carbon monoxide above most Solar System comet values.",
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        "qualification": "The authors warn that ratios among the other ions cannot directly determine neutral abundances; a decrease in CH+ with distance was only marginal."
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    "tags": [
      "3I/ATLAS",
      "interstellar comet",
      "spectroscopy"
    ],
    "image_url": null,
    "corrections": []
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  "sources": [
    {
      "source_id": "source-2026-09-08-016",
      "title": "arXiv preprint 2609.05393",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2609.05393",
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      "published_at": "2026-09-04T13:43:16.000-04:00",
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  "cite_this_report": {
    "title": "The Interstellar Comet's Tail Carried Unusual Nitrogen",
    "publisher": "The Machine Press",
    "published_at": "2026-09-08T09:00:00.000-04:00",
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