Compact Pebbles And The Evolution Of Volatiles In The Interstellar Comet 2I/Borisov

The interstellar traveler, 2I/Borisov, is the first clearly active extrasolar comet, ever detected in our Solar system.
We obtained high-resolution interferometric observations of 2I/Borisov with the Atacama Large Millimeter/submillimeter Array (ALMA), and multi-color optical observations with the Very Large Telescope (VLT) to gain a comprehensive understanding of the dust properties of this comet.

We found that the dust coma of 2I/Borisov consists of compact “pebbles” of radii exceeding ~1 mm, suggesting that the dust particles have experienced compaction through mutual impacts during the bouncing collision phase in the protoplanetary disk. We derived a dust mass loss rate of >= 200 kg/s and a dust-to-gas ratio >=3.

Our long term monitoring of 2I/Borisov with VLT indicates a steady dust mass loss with no significant dust fragmentation and/or sublimation occurring in the coma. We also detected emissions from carbon monoxide gas (CO) with ALMA and derived the gas production rate of Q(CO) (3.3+/-0.8)x10^{26} mole/s.

We found that the CO/H2O mixing ratio of 2I/Borisov changed drastically before and after perihelion, indicating the heterogeneity of the cometary nucleus, with components formed at different locations beyond the volatile snow-line with different chemical abundances. Our observations suggest that 2I/Borisov’s home system, much like our own system, experienced efficient radial mixing from the innermost parts of its protoplanetary disk to beyond the frost line of CO.

Bin Yang, Aigen Li, Martin A. Cordiner, Chin-Shin Chang, Olivier R. Hainaut, Jonathan P. Williams, Karen J. Meech, Jacqueline V. Keane, Eric Villard

Comments: 12 pages, 4 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
DOI: 10.1038/s41550-021-01336-w
Cite as: arXiv:2104.13545 [astro-ph.EP] (or arXiv:2104.13545v1 [astro-ph.EP] for this version)
Submission history
From: Bin Yang
[v1] Wed, 28 Apr 2021 02:48:16 UTC (743 KB)
https://arxiv.org/abs/2104.13545