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Peer-reviewedCC BYThe Astrophysical Journal Letters

Postperihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical Spectroscopy

  • Ruining Zhao1
  • Xiliang Zhang1,2
  • Bin Yang3,4
  • Xiangyu Fan1,2
  • Shu Min Wang1
  • Yang Huang2
  • Jifeng Liu5,1,2
5 affiliations
  1. 1Chinese Academy of Sciences
  2. 2University of Chinese Academy of Sciences
  3. 3Planetary Science Institute
  4. 4Universidad Diego Portales
  5. 5Beijing Normal University
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Abstract

We present multiepoch optical spectroscopy of the interstellar comet 3I/ATLAS obtained between 2025 December and 2026 January (heliocentric distances of 1.8–3.3 au), yielding postperihelion production rates and mixing ratios for CN, C 3 , C 2 , CH, and gaseous metals (Fe i and Ni i ). Our results show that the coma is less depleted in C 2 after perihelion than before, indicative of subsurface activation or compositional heterogeneity. The outgassing profiles reveal a pronounced perihelion asymmetry: the CN and metal production rates decline more gradually outbound than inbound, consistent with the reported behavior of H 2 O and implying a change in the comet’s activity pattern across perihelion. Despite being metal rich relative to its H 2 O content, 3I/ATLAS follows the metal–CO correlation observed in comets of diverse origins, suggesting that gaseous metal release is more closely linked to a CO-bearing volatile reservoir than to H 2 O, potentially in the form of metal carbonyls. In addition, the [O i ] λ 6300 emission shows a significant residual after subtracting the expected contributions from H 2 O, CO 2 , and CO, which may reflect systematic uncertainties in the photodissociation yields of those molecules or a contribution from additional oxygen-bearing parents.

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Cite

BibTeXRIS
BibTeX
@article{zhao2026postperihelion,
  title = {{Postperihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical Spectroscopy}},
  author = {Ruining Zhao and Xiliang Zhang and Bin Yang and Xiangyu Fan and Shu Min Wang and Yang Huang and Jifeng Liu},
  journal = {The Astrophysical Journal Letters},
  year = {2026},
  month = jun,
  doi = {10.3847/2041-8213/ae73fe},
  url = {https://doi.org/10.3847/2041-8213/ae73fe},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - Postperihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical Spectroscopy
AU  - Ruining Zhao
AU  - Xiliang Zhang
AU  - Bin Yang
AU  - Xiangyu Fan
AU  - Shu Min Wang
AU  - Yang Huang
AU  - Jifeng Liu
PY  - 2026
DA  - 2026/06/12
JO  - The Astrophysical Journal Letters
DO  - 10.3847/2041-8213/ae73fe
UR  - https://doi.org/10.3847/2041-8213/ae73fe
AB  - We present multiepoch optical spectroscopy of the interstellar comet 3I/ATLAS obtained between 2025 December and 2026 January (heliocentric distances of 1.8–3.3 au), yielding postperihelion production rates and mixing ratios for CN, C 3 , C 2 , CH, and gaseous metals (Fe i and Ni i ). Our results show that the coma is less depleted in C 2 after perihelion than before, indicative of subsurface activation or compositional heterogeneity. The outgassing profiles reveal a pronounced perihelion asymmetry: the CN and metal production rates decline more gradually outbound than inbound, consistent with the reported behavior of H 2 O and implying a change in the comet’s activity pattern across perihelion. Despite being metal rich relative to its H 2 O content, 3I/ATLAS follows the metal–CO correlation observed in comets of diverse origins, suggesting that gaseous metal release is more closely linked to a CO-bearing volatile reservoir than to H 2 O, potentially in the form of metal carbonyls. In addition, the [O i ] λ 6300 emission shows a significant residual after subtracting the expected contributions from H 2 O, CO 2 , and CO, which may reflect systematic uncertainties in the photodissociation yields of those molecules or a contribution from additional oxygen-bearing parents.
SN  - 2041-8205
SN  - 2041-8213
ER  -