LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité,
5 place Jules Janssen,
2 IRAM, Avd. Divina Pastora, 7, 18012 Granada, Spain
3 IRAM, 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
4 Commission des comètes, Société Astronomique de France, 3 rue Beethoven, 75016 Paris, France
5 Observatoire de Dauban, 04 Banon, France
6 NASA GSFC/USRA, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
7 Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA
8 NASA Goddard Center for Astrobiology, NASA GSFC, Mail Stop 690, Greenbelt, MD 20771, USA
Accepted: 12 September 2018
We present a multi-wavelength study of comet C/2016 R2 (PanSTARRS). This comet was observed on 23 and 24 January 2018 with the IRAM 30 m telescope, and in January to March 2018 with the Nançay radio telescope. Visible spectroscopy was performed in December 2017 and February 2018 with small amateur telescopes. We report on measurements of CO, CH3OH, H2CO and HCN production rates, and on the determination of the N2/CO abundance ratio. Several other species, especially OH, were searched for but not detected. The inferred relative abundances, including upper limits for sulfur species, are compared to those measured in other comets at about the same heliocentric distance of ~2.8 AU. The coma composition of comet C/2016 R2 is very different from all other comets observed so far, being rich in N2 and CO and dust poor. This suggests that this comet might belong to a very rare group of comets formed beyond the N2 ice line. Alternatively, comet C/2016 R2 (PanSTARRS) could be the fragment of a large and differentiated transneptunian object, with properties characteristic of volatile-enriched layers.
Key words: comets: general / comets: individual: C/2016 R2 / submillimeter: planetary systems / radio lines: planetary systems
Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).
The radio spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/619/A127
Astronomical Ring for Access to Spectroscopy (ARAS:http://astrosurf.com/aras/)
© ESO 2018
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.