Gemini detection of multiple fragments in C/2025 K1 (ATLAS)

ATel #17529; Bryce Bolin (Eureka Scientific), Marco Micheli (ESA NEO Coordination Centre), Davide Farnocchia (Jet Propulsion Laboratory, California Institute of Technology), Jennie Berghuis (Gemini Observatory), Emanuele Farina (Gemini Observatory), Brian Lemaux (Gemini Observatory), Matias Rodriguez (Gemini Observatory), Laura-May Abron (Griffith Observatory), Matthew Belyakov (Caltech), Christine Chen (STScI), Christoffer Fremling (Caltech), Oleksandra Ivanova (Slovak Academy of Sciences, Astronomical Institute), Ludmilla Kolokolova (University of Maryland), David Tholen (University of Hawaii), Ian Wong (STScI)
on 8 Dec 2025; 05:12 UT
Credential Certification: Bryce Bolin (bolin.astro@gmail.com)

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We follow up on the observations of the fragmenting Oort cloud comet C/2025 K1 (hereafter K1) described in previous ATels #17482, #17488, #17495, #17500, #17501, #17510. Using the Gemini North 8.1-m telescope and the Gemini Multi-Object Spectrograph (GMOS) instrument, we have imaged several fragments in the coma of K1 on 2025 December 6, 08:47:25 UTC (under program GN-2025B-DD-113/PI: Bolin). The images were taken in 0.7 arcsec seeing and had a 3 s exposure time in r-band (630 nm effective wavelength), showing at least four possible pieces spread out over ~10 arcsec, and a tail ~30 arcsec in length, at least ~4,000 km and 12,000 km at the 0.55 au distance of the comet. The orientation of the trail of fragments in the dust tail has a position angle of ~215 degrees, similar in value to the projected anti-solar direction on this date. The heliocentric distance and phase angle of the comet at the time of these observations are 1.4 au and 32.4 degrees. Attached are unlabeled and labeled images of the comet and its fragments in a 3s r-band exposure. North is up, and east is to the left in these images. The projected solar and heliocentric orbital velocity vectors are shown in orange and blue, respectively. Going from west to east, there are two fragments ~2 arcsec apart, a dusty, diffuse source co-moving with the comet, followed by the fourth fragment. The brightnesses of the fragments measured in a 0.81 arcsec radius aperture, going from west to east, are: 18.55 +/- 0.02, 18.74 +/- 0.03, 18.99 +/- 0.04, 16.94+/-0.01. This study is based on observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership. This work was enabled by observations made from the Gemini North telescope, located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are grateful for the privilege of observing the Universe from a place unique in both its astronomical quality and cultural significance.

r-band images of C/2025 K1 (ATLAS) taken on 2025 December 6 UTC