![Images acquired on 2019 October 4 (left) and 27 (right) with LDT. The top row show stacks of r and CN images, respectively. The bottom row shows the same images enhanced by subtraction of an azimuthal median profile. The enhanced CN images have been smoothed with a Gaussian profile to better reveal the faint underlying structure. A compass indicating north (N), east (E), the anti-sunward direction (ββ), and the anti-velocity vector (βv) are overlaid on the r panels, while a scale bar showing a distance at the comet of 20,000 km is given on the CN panels (1 arcsec corresponds to 2134 km on October 4 and 1814 km on October 27). All four panels for a given night have the same orientation and physical scale at the comet. The October 4 image is a single frame and shows several artifacts that could not be removed without a median combination include several bright pixels in the CN frame (yellow) and a bad column in all frames (black diagonal line). On October 4, a bright star is seen near the left edge of the r frames and as a diagonal (yellow) line in the upper right in CN. Two faint trailed stars are visible in the r images on October 27. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/The-Highly.png?fit=1200%2C677&ssl=1)
[astro-ph.EP]. We report on imaging, spectroscopy, and narrowband photometry of interstellar comet 2I/Borisov obtained at Lowell Observatory from 2019 September 13 to December 16.
We measured chemical composition on four nights before perihelion, from October 4 to November 25 (2.466 to 2.028 au), with CN detections on all nights. Our measurements from October 27 represent the earliest reported detections of C2 and C3, where C2-to-CN and C3-to-CN log production rate ratios were β0.7 and β1.3, respectively.
Both ratios increased by nearly 4Γ to β0.3 and β0.9 by November 25, an extremely large increase with heliocentric distance that is unprecedented in the Lowell Observatory comet database. We additionally observed OH and NH on November 25, with a derived H2O production rate of 4.5Γ1026 mol sβ1 and very high log production rate ratios for CN-to-OH (β2.0) and NH-to-OH (β1.7).
Monitoring from broadband R images from September 13 to December 16 suggests dust (A(0β)fΟ) production peaked around October 19, 50 days before its December 8 perihelion passage. Narrowband images from October 4 and 27 reveal a nearly symmetric CN distribution in Borisov’s coma, suggesting activity over its entire sunward hemisphere and possibly its entire nucleus.
Our results, combined with those from others, reveal a chemical composition and behavior with heliocentric distance unlike any other comet we have observed.
Allison N. Bair, David G. Schleicher, Theodore Kareta, Matthew M. Knight, Michael S.P. Kelley
Comments: 26 pages, 7 figures, 5 tables. Accepted for publication in the Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2608.23701 [astro-ph.EP] (or arXiv:2608.23701v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.23701
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Submission history
From: Matthew Knight
[v1] Mon, 24 Aug 2026 18:00:17 UTC (1,488 KB)
https://arxiv.org/abs/2608.23701
Astrobiology, Astronomy, Astrochemistry, Interstellar,
