Electronic Telegram No. 5564 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET C/2025 K3 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on May 23 with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below, along with pre-discovery observations made on Apr. 28 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (and identified by Weryk later). 2025 UT R.A. (2000) Decl. Mag. Apr. 28.58346 19 31 29.40 +50 47 39.3 22.1 28.58476 19 31 29.38 +50 47 39.7 22.2 28.59279 19 31 29.24 +50 47 42.3 22.3 28.59409 19 31 29.20 +50 47 42.5 22.6 28.60367 19 31 29.06 +50 47 45.9 22.1 28.61286 19 31 28.90 +50 47 49.2 22.4 May 23.53992 19 21 31.91 +52 54 54.7 22.0 23.54941 19 21 31.60 +52 54 57.7 21.9 23.55890 19 21 31.28 +52 54 59.8 21.4 23.56843 19 21 30.97 +52 55 02.7 21.6 Weryk adds that three 60-s gri-band follow-up exposures taken on May 24.6 UT with the 3.6-m Canada-France-Hawaii Telescope (queue observer J. Nagasako; queue coordinator V. Khatu) confirm this to be a comet; a single image taken in 0".6 seeing shows a very condensed head of size 1".0 (full-width-at-half- maximum) shows a tail about 2" long in p.a. 170 degrees. Three additional 60-s CFHT images taken on June 3.55 (queue observer A. Acohido; queue coordinator H. Flewelling) also show the 2" tail in p.a. 170 degrees; a single image taken in 0".8 seeing shows a very condensed head of size 1".2 (FHWM). The available astrometry appears on MPEC 2025-L42. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 31 observations spanning 2025 Apr. 28-June 3 (mean residual 0".2). The comet will pass 2.23 AU from Jupiter on 2028 Sept. 2 UT. T = 2028 Dec. 14.56789 TT Peri. = 188.73351 Node = 350.63634 2000.0 q = 3.4623627 AU Incl. = 104.93798 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 7.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 05 25 19 20.74 +53 01.4 10.565 10.702 95.0 5.4 20.9 2025 06 04 19 14.76 +53 41.6 10.459 10.640 97.5 5.4 20.8 2025 06 14 19 07.88 +54 13.5 10.361 10.579 99.7 5.4 20.8 2025 06 24 19 00.30 +54 35.7 10.272 10.518 101.3 5.4 20.7 2025 07 04 18 52.26 +54 47.0 10.192 10.456 102.3 5.5 20.7 2025 07 14 18 44.07 +54 47.0 10.122 10.395 102.8 5.5 20.7 2025 07 24 18 36.03 +54 35.7 10.063 10.333 102.6 5.5 20.6 2025 08 03 18 28.45 +54 13.5 10.014 10.271 101.9 5.5 20.6 2025 08 13 18 21.59 +53 41.6 9.974 10.209 100.6 5.6 20.6 2025 08 23 18 15.65 +53 01.4 9.944 10.147 98.8 5.7 20.5 2025 09 02 18 10.78 +52 14.6 9.921 10.085 96.5 5.7 20.5 2025 09 22 18 04.50 +50 29.6 9.892 9.961 91.0 5.8 20.5 2025 10 12 18 02.73 +48 42.1 9.876 9.836 84.8 5.8 20.4 2025 11 01 18 04.89 +47 06.2 9.857 9.711 78.7 5.8 20.4 2025 11 21 18 10.11 +45 53.1 9.820 9.586 73.5 5.7 20.3 2025 12 11 18 17.43 +45 10.9 9.755 9.460 69.8 5.6 20.3 2025 12 31 18 25.82 +45 04.7 9.653 9.334 68.3 5.6 20.2 2026 01 20 18 34.26 +45 36.5 9.512 9.207 69.1 5.7 20.1 2026 02 09 18 41.66 +46 45.6 9.334 9.081 72.2 5.9 20.0 2026 03 01 18 46.86 +48 27.8 9.127 8.953 76.8 6.2 19.9 2026 03 21 18 48.60 +50 35.8 8.903 8.826 82.3 6.4 19.8 2026 04 10 18 45.56 +52 57.9 8.676 8.698 87.9 6.6 19.7 2026 04 30 18 36.53 +55 17.8 8.461 8.570 92.8 6.7 19.6 2026 05 20 18 20.91 +57 15.0 8.269 8.441 96.4 6.8 19.5 2026 06 09 17 59.52 +58 27.8 8.112 8.313 97.9 6.9 19.4 2026 06 29 17 35.16 +58 40.1 7.992 8.184 97.3 7.1 19.3 2026 07 19 17 11.99 +57 48.3 7.910 8.054 94.5 7.2 19.2 2026 08 08 16 53.63 +56 03.0 7.859 7.925 90.0 7.4 19.2 2026 08 28 16 41.80 +53 44.2 7.827 7.795 84.5 7.4 19.1 2026 09 17 16 36.45 +51 13.7 7.800 7.665 78.6 7.4 19.0 2026 10 07 16 36.61 +48 50.7 7.763 7.535 73.2 7.3 19.0 2026 10 27 16 41.01 +46 50.2 7.702 7.404 69.0 7.2 18.9 2026 11 16 16 48.34 +45 23.4 7.606 7.274 66.8 7.2 18.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 June 6 (CBET 5564) Daniel W. E. Green