![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 (−⊙), and the anti-velocity vector (−v) 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 −0.7 and −1.3, respectively.
Both ratios increased by nearly 4× to −0.3 and −0.9 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 4.5×1026 mol s−1 and very high log production rate ratios for CN-to-OH (−2.0) and NH-to-OH (−1.7).
Monitoring from broadband R images from September 13 to December 16 suggests dust (A(0∘)fρ) 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
Focus to learn more
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,
