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Peer-reviewedCC BYThe Open Journal of Astrophysics

JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS

  • Jason T. Hinkle1
  • Bin Yang2
  • Karen J. Meech3
  • Andrew Hoffman4
  • Benjamin J. Shappee5
  • W. B. Hoogendam6
  • James J. Wray7
7 affiliations
  1. 1ORCID iD: 0000-0001-9668-2920
  2. 2ORCID iD: 0000-0002-5033-9593
  3. 3ORCID iD: 0000-0002-2058-5670
  4. 4ORCID iD: 0000-0002-8732-6980
  5. 5ORCID iD: 0000-0003-4631-1149
  6. 6ORCID iD: 0000-0003-3953-9532
  7. 7ORCID iD: 0000-0001-5559-2179
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Abstract

Interstellar objects (ISOs), particularly those with cometary activity, provide unique insight into the primordial physical and chemical conditions present during the formation of the planetary system in which they originated. Observations in the sub-mm regime allow for direct measurements of several parent molecules released from the comet nucleus into the coma. Here we present observations of the third ISO, 3I/ATLAS, with the heterodyne receiver on the James Clerk Maxwell Telescope (JCMT), which targeted emission from HCN( J = 3 − 2 ) and CO( J = 2 − 1 ). Our observations, taken between 16 July 2025 and 21 July 2025 (UT), when 3I/ATLAS was at a heliocentric distance between 4.01 and 3.84 au, provide the earliest sub-mm constraints on its activity. We do not detect HCN or CO in these epochs, with 3 σ upper-limits on the production rates of Q ( H C N ) < 1.7 × 10 24 s at r h = 4.01 − 3.97 au and Q ( C O ) < 1.1 × 10 27 s at r h = 3.94 − 3.84 au, respectively. We combine this HCN limit with later JCMT observations of HCN to constrain its temporal evolution. Fitting the HCN detections with a Q ( H C N ) ∝ r h − n model and accounting for the upper-limits yields n = 12.7 − 2.5 + 6.9 . This slope is steeper than those of typical Solar System comets, but consistent with the production rate slopes measured for other species in the coma of 3I/ATLAS.

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Cite

BibTeXRIS
BibTeX
@article{hinkle2026jcmt,
  title = {{JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS}},
  author = {Jason T. Hinkle and Bin Yang and Karen J. Meech and Andrew Hoffman and Benjamin J. Shappee and W. B. Hoogendam and James J. Wray},
  journal = {The Open Journal of Astrophysics},
  year = {2026},
  month = jun,
  doi = {10.33232/001c.163250},
  url = {https://doi.org/10.33232/001c.163250},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS
AU  - Jason T. Hinkle
AU  - Bin Yang
AU  - Karen J. Meech
AU  - Andrew Hoffman
AU  - Benjamin J. Shappee
AU  - W. B. Hoogendam
AU  - James J. Wray
PY  - 2026
DA  - 2026/06/12
JO  - The Open Journal of Astrophysics
DO  - 10.33232/001c.163250
UR  - https://doi.org/10.33232/001c.163250
AB  - Interstellar objects (ISOs), particularly those with cometary activity, provide unique insight into the primordial physical and chemical conditions present during the formation of the planetary system in which they originated. Observations in the sub-mm regime allow for direct measurements of several parent molecules released from the comet nucleus into the coma. Here we present observations of the third ISO, 3I/ATLAS, with the heterodyne receiver on the James Clerk Maxwell Telescope (JCMT), which targeted emission from HCN( J = 3 − 2 ) and CO( J = 2 − 1 ). Our observations, taken between 16 July 2025 and 21 July 2025 (UT), when 3I/ATLAS was at a heliocentric distance between 4.01 and 3.84 au, provide the earliest sub-mm constraints on its activity. We do not detect HCN or CO in these epochs, with 3 σ upper-limits on the production rates of Q ( H C N ) < 1.7 × 10 24 s at r h = 4.01 − 3.97 au and Q ( C O ) < 1.1 × 10 27 s at r h = 3.94 − 3.84 au, respectively. We combine this HCN limit with later JCMT observations of HCN to constrain its temporal evolution. Fitting the HCN detections with a Q ( H C N ) ∝ r h − n model and accounting for the upper-limits yields n = 12.7 − 2.5 + 6.9 . This slope is steeper than those of typical Solar System comets, but consistent with the production rate slopes measured for other species in the coma of 3I/ATLAS.
SN  - 2565-6120
ER  -