Electronic Telegram No. 5558 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 K2 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on May 29 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (discovery astrometry tabulated below). Three 45-s w-band survey images taken in 1".5 seeing show a diffuse head of size 2".1 (full-width-at-half-maximum) with a tail about 3" long in p.a. 290 degrees. 2025 UT R.A. (2000) Decl. Mag. May 29.53372 20 42 04.92 -34 52 16.2 20.4 29.54217 20 42 04.47 -34 52 28.9 20.2 29.55061 20 42 03.99 -34 52 41.8 20.5 29.60499 20 42 01.02 -34 54 05.1 20.7 29.60563 20 42 00.98 -34 54 06.0 20.9 Weryk obtained (with R. Wainscoat) three 60-s gri-band exposures with the 3.6-m Canada-France-Hawaii Telescope on May 30.6 UT (queue observer A. Acohido; queue coordinator H. Flewelling) that confirm this to be a comet. In an image taken in 1".1 seeing, there is a condensed head of size 1".4-1".5 (FWHM) with a broad tail > 30" long spanning p.a. 275-300 degrees. The available astrometry appears on 2025-L17. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 14 observations spanning May 29-June 2 (mean residual 0".3). There are no close approaches to major planets. T = 2025 Oct. 20.77290 TT Peri. = 232.03962 Node = 114.19719 2000.0 q = 2.8820707 AU Incl. = 114.66529 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 05 05 20 52.36 -26 21.8 3.078 3.340 96.1 17.5 20.6 2025 05 15 20 50.56 -29 23.0 2.855 3.292 106.7 17.1 20.4 2025 05 25 20 45.63 -33 00.8 2.647 3.245 117.8 16.0 20.2 2025 06 04 20 36.49 -37 16.5 2.465 3.201 129.0 14.3 20.0 2025 06 14 20 21.83 -42 03.8 2.317 3.159 139.6 12.0 19.8 2025 06 24 20 00.08 -47 05.9 2.213 3.120 147.7 10.0 19.7 2025 07 04 19 29.95 -51 53.1 2.160 3.083 150.1 9.5 19.6 2025 07 14 18 51.71 -55 49.0 2.160 3.049 145.1 11.0 19.5 2025 07 24 18 08.47 -58 25.8 2.210 3.018 135.4 13.7 19.6 2025 08 03 17 26.00 -59 39.2 2.301 2.990 124.1 16.3 19.6 2025 08 13 16 49.63 -59 49.2 2.423 2.965 112.7 18.4 19.7 2025 08 23 16 21.70 -59 24.3 2.566 2.943 101.7 19.7 19.8 2025 09 02 16 02.01 -58 48.3 2.718 2.924 91.5 20.2 19.9 2025 09 12 15 49.09 -58 16.4 2.873 2.909 82.0 20.0 20.0 2025 09 22 15 41.42 -57 56.2 3.021 2.897 73.3 19.4 20.1 2025 10 02 15 37.73 -57 51.4 3.159 2.888 65.4 18.4 20.2 2025 10 12 15 37.00 -58 03.1 3.281 2.883 58.3 17.1 20.3 2025 10 22 15 38.52 -58 31.3 3.384 2.882 52.1 15.8 20.3 2025 11 01 15 41.72 -59 16.1 3.466 2.884 47.2 14.6 20.4 2025 11 11 15 46.16 -60 17.1 3.525 2.890 43.6 13.7 20.4 2025 11 21 15 51.49 -61 34.4 3.561 2.899 41.7 13.1 20.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 June 2 (CBET 5558) Daniel W. E. Green