Is Comet C/2023 R1 (PanStarrs) undergoing a full fragmentation process?

ATel #17929; Federico Manzini (Stazione Astronomica di Sozzago, Italy), Mohamed F. Aboushelib (National Research Institute of Astronomy and Geophysics, Cairo-Egypt), A. Eid Abdelaziz (National Research Institute of Astronomy and Geophysics, Cairo-Egypt), Virginio Oldani (Stazione Astronomica di Sozzago, Italy), Costantino Sigismondi (ICRANet Pescara and UPRA Roma, Italy), Andrea Brucato (Sapienza University of Rome, Italy), Luigi R. Bedin (OAPd-INAF, Italy), Alessandra Mura (UniPD, INAF, Italy), Andrea Farina (UniPD, Italy), Paolo Ochner (INAF, UniPD, Italy)
on 28 Jul 2026; 21:58 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Costantino Sigismondi (sigismondi@icra.it)

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The timeline of the discovery of the possible fragmentation of the Comet C/2023 R1 (PanStarrs) is well described in ATEL#17915. Possible further clues of fragmentation can be seen in the images published by J.F. Soulier and J.G. Bosch (https://lesia.obspm.fr/comets/lib/all-obs-table.php? Code=CK23R010&y1=1908&m1=01 ). Public images from the LCO Science Archive (https://archive.lco.global/ ), obtained with the 2-m LCO OGG telescope (proposal TS02026A-020; authors listed in ATEL#17915), clearly show two condensations adjacent to the nucleus in the images from 15 and 18 July 2026. We also dedicated a full observing session to this Comet with the 1.88 m Kottamia reflecting telescope (NRIAG, Egypt, located in the desert East of Cairo) on the night of 19 July. We measured the positions of the two condensations, designated bodies B and C in the accompanying file https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C2023R1/Comet2023R1captions.pdf and we calculated their distances from the main nucleus in arcsec projected on the sky plane (Figure 4). The measurements errors are estimated at +/- 0.133 arcsec for the LCO images, and +/- 0.237 arcsec for the Kottamia image. The measured distances were converted into kilometers, corrected for the distance from Earth and for the velocity vector angle (assuming that all fragments follow the main nucleus on the same orbit, see Figure 5). The corresponding positional measurements are included in the dedicated directory (https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/ATel/C2023R1/ ). Over these days, body C clearly faded, while body B appeared to increase in apparent size. This behavior suggests that the features are dust clouds composed of multiple clumps moving away from the nucleus. The distances measured show a slight increase of the separation velocity of bodies B and C from the main nucleus. The acceleration of bodies B and C, emerging from the data, may be due to the solar radiation pressure. A careful inspection of the LCO images revealed an additional weak condensation very close to the nucleus and moving away from it (Figure 2). This body D is visible only as a very faint trace in the images obtained at the Kottamia observatory (Figure 3). Precise astrometric measurements could not be performed because this additional fragment lacks sufficient condensation. The undergoing fragmentation is occurring with the Comet more than 3.5 AU from the Sun, and almost three months after perihelion.

Dossier C2023R1 fragmentation: Calibration details, figures and captions