Science and Exploration

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

By Keith Cowing

Press Release

April 28, 2021

Filed under comet, Interstellar

Compact Pebbles And The Evolution Of Volatiles In The Interstellar Comet 2I/Borisov — ALMA dust thermal continuum maps of 2I/Borisov at 0.85, 1.27, 2.15 and 2.84mm. The observations of the dust thermal continuum emission for the coma around the ISO 2I/Borisov were made at a heliocentric distance of rh ? 2.01 au and a geocentric distance of ? ? 2.03 au. The color-bar indicates the thermal emission intensity in Jansky. The projected position angles of the extended Sun-to-target vector and dust-tail orientation on 2019 December 03 are labeled on the lower right. The FWHM of the spatial resolution element for each band is labeled on the lower left.

astro-ph.EP

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

Keith Cowing

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.

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