Open AccessCold Traps of Hypervolatiles in the Protosolar Nebula at the Origin of the Peculiar Composition of Comet C/2016 R2 (PanSTARRS)
Author(s) -
Olivier Mousis,
Artyom Aguichine,
Alexis Bouquet,
Jonathan I. Lunine,
Grégoire Danger,
K. Mandt,
A. LuspayKuti
Publication year - 2021
Publication title -
the planetary science journal
Language(s) - English
Resource type - Journals
ISSN - 2632-3338
DOI - 10.3847/psj/abeaa7
Subject(s) - comet , nebula , physics , coma (optics) , astrophysics , interstellar comet , composition (language) , abundance (ecology) , astrobiology , water ice , line (geometry) , linguistics , stars , philosophy , geometry , mathematics , fishery , biology
Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N 2 /CO abundance ratio, typically larger than ∼0.05, and at least 2–3 times higher than the one measured in 67P/Churyumov–Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H 2 O (H 2 O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed low water abundance. We then alternatively investigate the possibility that the building blocks of R2 agglomerated from grains and pebbles made of pure condensates via the use of a disk model describing the radial transport of volatiles. We show that N 2 /CO ratios reproducing the value estimated in this comet can be found in grains condensed in the vicinity of the CO and N 2 ice lines. Moreover, high CO/H 2 O ratios (>100 times the initial gas-phase value) can be found in grains condensed in the vicinity of the CO ice line. If the building blocks of a comet assembled from such grains, they should present N 2 /CO and CO/H 2 O ratios consistent with the measurements made in R2’s coma. Our scenario indicates that R2 formed in a colder environment than the other comets that share more usual compositions. Our model also explains the unusual composition of the interstellar comet 2l/Borisov.