[en] Comets spend most of their lives at large distances from any star, during which time their interior compositions remain relatively unaltered. Cometary observations can therefore provide direct insight into the chemistry that occurred during their birth at the time of planet formation. To date, there have been no confirmed observations of parent volatiles (gases released directly from the nucleus) of a comet from any planetary system other than our own. Here, we present high-resolution interferometric observations of 2I/Borisov, the first confirmed interstellar comet, obtained using the Atacama Large Millimeter/submillimeter Array (ALMA) on 15-16 December 2019. Our observations reveal emission from hydrogen cyanide (HCN) and carbon monoxide (CO) coincident with the expected position of 2I/Borisov's nucleus, with production rates Q(HCN) = (7.0 ± 1.1) × 10[SUP]23[/SUP] s[SUP]-1[/SUP] and Q(CO) = (4.4 ± 0.7) × 10[SUP]26[/SUP] s[SUP]-1[/SUP]. While the HCN abundance relative to water (0.06-0.16%) appears similar to that of typical, previously observed comets in our Solar System, the abundance of CO (35-105%) is among the highest observed in any comet within 2 au of the Sun. This shows that 2I/Borisov must have formed in a relatively CO-rich environment—probably beyond the CO ice-line in the very cold, outer regions of a distant protoplanetary accretion disk, as part of a population of small icy bodies analogous to our Solar System's own proto-Kuiper belt.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Cordiner, M. A.; Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA ; Department of Physics, Catholic University of America, Washington DC, USA
Milam, S. N.; Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
Biver, N.; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
Bockelée-Morvan, D.; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
Roth, N. X.; Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA ; Universities Space Research Association, Columbia, MD, USA
Bergin, E. A.; Department of Astronomy, University of Michigan, Ann Arbor, MI, USA
Jehin, Emmanuel ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Remijan, A. J.; National Radio Astronomy Observatory, Charlottesville, VA, USA
Charnley, S. B.; Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
Mumma, M. J.; Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
Boissier, J.; IRAM, Saint Martin d'Heres, France
Crovisier, J.; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
Paganini, L.; NASA Headquarters, Washington DC, USA
Kuan, Y.-J.; National Taiwan Normal University, Taipei, Taiwan, ROC
Lis, D. C.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA)
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