CH$_3$OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH$_3$OH/HCN Production Rate Ratio
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| Autores principales: | , , , , , , , , , , , , , , , , , |
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| Formato: | Preprint |
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2025
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| _version_ | 1866908860974891008 |
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| author | Roth, Nathan X. Cordiner, Martin A. Bockelée-Morvan, Dominique Biver, Nicolas Crovisier, Jacques Milam, Stefanie N. Lellouch, Emmanuel Santos-Sanz, Pablo Lis, Dariusz C. Qi, Chunhua Foster, K. D. Boissier, Jérémie Furuya, Kenji Moreno, Raphael Charnley, Steven B. Remijan, Anthony J. Kuan, Yi-Jehng Hart, Lillian X. |
| author_facet | Roth, Nathan X. Cordiner, Martin A. Bockelée-Morvan, Dominique Biver, Nicolas Crovisier, Jacques Milam, Stefanie N. Lellouch, Emmanuel Santos-Sanz, Pablo Lis, Dariusz C. Qi, Chunhua Foster, K. D. Boissier, Jérémie Furuya, Kenji Moreno, Raphael Charnley, Steven B. Remijan, Anthony J. Kuan, Yi-Jehng Hart, Lillian X. |
| contents | We report the detection of methanol (CH$_3$OH) toward interstellar comet 3I/ATLAS using the Atacama Compact Array of the Atacama Large Millimeter/Submillimeter Array (ALMA) on UT 2025 August 28, September 18 and 22, and October 1, and of hydrogen cyanide (HCN) on September 12 and 15. These observations spanned pre-perihelion heliocentric distances ($r_H$) of 2.6 -- 1.7 au. The molecules showed outgassing patterns distinct from one another, with HCN production being depleted in the sunward hemisphere of the coma, whereas CH$_3$OH was enhanced in that direction. Statistical analysis of molecular scale lengths in 3I/ATLAS indicated that CH$_3$OH included production from coma sources at $L_p>258$ km at 99% confidence. However low signal-to-noise on long baselines, which sample emission on small spatial scales closest to the nucleus, prevented definitively ruling out CH$_3$OH as purely a parent species. In contrast, HCN production was indistinguishable from direct nucleus sublimation. The CH$_3$OH production rate increased sharply from August through October, including an uptick near the inner edge of the H$_2$O sublimation zone at $r_H$ = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH$_3$OH/HCN ratios in 3I/ATLAS of $124^{+30}_{-34}$ and $79^{+11}_{-14}$ on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS). |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_20845 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | CH$_3$OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH$_3$OH/HCN Production Rate Ratio Roth, Nathan X. Cordiner, Martin A. Bockelée-Morvan, Dominique Biver, Nicolas Crovisier, Jacques Milam, Stefanie N. Lellouch, Emmanuel Santos-Sanz, Pablo Lis, Dariusz C. Qi, Chunhua Foster, K. D. Boissier, Jérémie Furuya, Kenji Moreno, Raphael Charnley, Steven B. Remijan, Anthony J. Kuan, Yi-Jehng Hart, Lillian X. Earth and Planetary Astrophysics Astrophysics of Galaxies We report the detection of methanol (CH$_3$OH) toward interstellar comet 3I/ATLAS using the Atacama Compact Array of the Atacama Large Millimeter/Submillimeter Array (ALMA) on UT 2025 August 28, September 18 and 22, and October 1, and of hydrogen cyanide (HCN) on September 12 and 15. These observations spanned pre-perihelion heliocentric distances ($r_H$) of 2.6 -- 1.7 au. The molecules showed outgassing patterns distinct from one another, with HCN production being depleted in the sunward hemisphere of the coma, whereas CH$_3$OH was enhanced in that direction. Statistical analysis of molecular scale lengths in 3I/ATLAS indicated that CH$_3$OH included production from coma sources at $L_p>258$ km at 99% confidence. However low signal-to-noise on long baselines, which sample emission on small spatial scales closest to the nucleus, prevented definitively ruling out CH$_3$OH as purely a parent species. In contrast, HCN production was indistinguishable from direct nucleus sublimation. The CH$_3$OH production rate increased sharply from August through October, including an uptick near the inner edge of the H$_2$O sublimation zone at $r_H$ = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH$_3$OH/HCN ratios in 3I/ATLAS of $124^{+30}_{-34}$ and $79^{+11}_{-14}$ on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS). |
| title | CH$_3$OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH$_3$OH/HCN Production Rate Ratio |
| topic | Earth and Planetary Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2511.20845 |