Electronic Telegram No. 5579 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 M3 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on June 30 (discovery observations tabulated below, noting a possible extended point- spread function then, but "too close to neighboring stars and a CCD cell gap to be sure". 2025 UT R.A. (2000) Decl. Mag. June 30.37271 16 48 21.30 -11 17 39.7 21.3 30.38416 16 48 20.70 -11 17 41.5 21.0 Weryk and R. Wainscoat arranged follow-up observations with the 3.6-m Canada- France-Hawaii Telescope at Mauna Kea, and three 60-s gri-band images were taken on July 1.3 UT (queue observer J. Silva; queue coordinator N. Manset) that show this object to be "an obvious comet"; in the best image obtained in 0".7 seeing, there was a very condensed head of size 1".1 (full-width-at-half- maximum) and a straight 8" tail toward p.a. 70 degrees. Weryk then was able to find four 45-s w-band pre-discovery images of this comet that were obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on June 22.33-22.37; from the two exposures that did not have the comet obstructed by stars, there was a condensed head of size 1".9 (FWHM) and mag 20.8-21.3 in 1".4 seeing, with a tail about 5" long in p.a. 65 degrees. The available astrometry appears on MPEC 2025-N75. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 21 observations spanning June 22-July 5 (mean residual 0".3). There are no close approaches to major planets. T = 2026 July 23.25112 TT Peri. = 197.02507 Node = 65.35410 2000.0 q = 6.4712152 AU Incl. = 137.22641 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 9.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 06 14 17 03.18 -10 38.2 6.028 7.018 166.0 2.0 20.2 2025 06 24 16 54.01 -11 01.5 6.040 6.992 158.0 3.1 20.2 2025 07 04 16 45.24 -11 27.2 6.086 6.967 147.7 4.5 20.2 2025 07 14 16 37.14 -11 55.1 6.165 6.943 137.0 5.7 20.2 2025 07 24 16 29.94 -12 24.9 6.271 6.919 126.2 6.8 20.2 2025 08 03 16 23.79 -12 56.4 6.399 6.896 115.4 7.6 20.2 2025 08 13 16 18.77 -13 29.3 6.543 6.873 104.9 8.2 20.3 2025 08 23 16 14.91 -14 03.4 6.696 6.851 94.5 8.5 20.3 2025 09 02 16 12.19 -14 38.5 6.854 6.829 84.4 8.5 20.4 2025 09 12 16 10.53 -15 14.3 7.009 6.808 74.5 8.2 20.4 2025 09 22 16 09.85 -15 50.7 7.156 6.788 64.7 7.7 20.4 2025 10 02 16 10.05 -16 27.4 7.291 6.768 55.1 7.0 20.5 2025 10 12 16 11.01 -17 04.4 7.410 6.749 45.5 6.1 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 July 9 (CBET 5579) Daniel W. E. Green