{
  "abstract": "We report on imaging, spectroscopy, and narrowband photometry of interstellar comet 2I/Borisov obtained at Lowell Observatory from 2019 September 13 to December 16. We measured chemical composition on 4 nights before perihelion, from October 4 to November 25 (2.466–2.028 au), with CN detections on all nights. Our measurements from October 27 represent the earliest reported detections of C ₂ and C ₃ , where C ₂ -to-CN and C ₃ -to-CN log production rate ratios were −0.7 and −1.3, respectively. Both ratios increased by nearly 4× to −0.3 and −0.9 by November 25, an extremely large increase with heliocentric distance that is unprecedented in the Lowell Observatory comet database. We additionally observed OH and NH on November 25, with a derived H ₂ O production rate of 4.5 × 10 ²⁶ mol s ⁻¹ and very high log production rate ratios for CN-to-OH (−2.0) and NH-to-OH (−1.7). Monitoring from broadband R images from September 13 to December 16 suggests dust ( A (0°) fρ ) production peaked around October 19, 50 days before its December 8 perihelion passage. Narrowband images from October 4 and 27 reveal a nearly symmetric CN distribution in Borisov’s coma, suggesting activity over its entire sunward hemisphere and possibly its entire nucleus. Our results, combined with those from others, reveal a chemical composition and behavior with heliocentric distance unlike any other comet we have observed.",
  "abstract_shown": true,
  "affiliations": [
    "Lowell Observatory",
    "Villanova University",
    "United States Naval Academy",
    "University of Maryland"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Allison N. Bair",
      "orcid": "0009-0006-9319-5645"
    },
    {
      "affs": [
        0
      ],
      "name": "David G. Schleicher",
      "orcid": "0000-0003-1412-2511"
    },
    {
      "affs": [
        1
      ],
      "name": "Theodore Kareta",
      "orcid": "0000-0003-1008-7499"
    },
    {
      "affs": [
        2
      ],
      "name": "Matthew M. Knight",
      "orcid": "0000-0003-2781-6897"
    },
    {
      "affs": [
        3
      ],
      "name": "Michael S. P. Kelley",
      "orcid": "0000-0002-6702-7676"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/emme6mzk5v2dv.bib",
  "cited_by": 0,
  "doi": "10.3847/psj/ae9f3d",
  "fulltext_url": null,
  "id": "emme6mzk5v2dv",
  "issns": [
    "2632-3338"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/PSJ/ae9f3d",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Astro and Planetary Science"
    ]
  ],
  "openalex": "W7204246261",
  "pdf_url": "https://iopscience.iop.org/article/10.3847/PSJ/ae9f3d/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-09",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/emme6mzk5v2dv.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:16Z",
      "native_id": "10.3847/psj/ae9f3d",
      "source": "crossref",
      "url": "https://iopscience.iop.org/article/10.3847/PSJ/ae9f3d"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Astro and Planetary Science",
      "subfield": "planetary"
    }
  ],
  "title": "The Highly Unusual Behavior and Chemical Composition of Interstellar Comet 2I/Borisov",
  "title_text": "The Highly Unusual Behavior and Chemical Composition of Interstellar Comet 2I/Borisov",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:16Z",
  "url": "https://research.draconitic.com/paper/emme6mzk5v2dv",
  "venue": "The Planetary Science Journal",
  "versions": []
}