Electronic Telegram No. 5650 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 X1 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on 2025 Dec. 12 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, when four 45-s w-band survey images revealed a very condensed head of size 1".7 (full-width-at-half-maximum) in 1".1-1".3 seeing with a possible short tail about 1" long in p.a. 265 degrees. The discovery observations are tabulated below. 2025 UT R.A. (2000) Decl. Mag. Dec. 12.62558 10 15 29.21 +38 58 54.5 21.0 12.63380 10 15 29.35 +38 58 57.9 21.2 12.64204 10 15 29.48 +38 59 01.4 20.9 12.65025 10 15 29.61 +38 59 04.8 21.0 The object was accidentally rediscovered on four 45-s w-band survey images taken with the Pan-STARRS2 reflector on 2025 Dec. 24.6 UT in 0".8-0".9 seeing; a stack of the three best images show a very condensed head of size 1".41 (FWHM) and a tail about 4" long toward p.a. 265 degrees. Three 60-s follow-up gri-band images were obtained on 2025 Dec. 13.6 by Weryk and R. Wainscoat with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea (queue observer J. Nagasako; queue coordinator H. Flewelling) in 0".7 seeing that show a very condensed head of size 1".1 (FWHM) and a clear 8"-long tail in p.a. 265 deg. Three additional stacked 60-s CFHT images obtained on 2025 Dec. 22.6 (queue observer L. Wells; queue coordinator V. Khatu) in 0".7-0".8 seeing show a condensed head of size 1".1 (FWHM) and a straight tail about 4" long toward p.a. 270 degrees. The available astrometry appears on MPEC 2026-A15, and includes pre-discovery observations obtained with the 1.2-m Schmidt reflector at Palomar on 2025 Dec. 11.1 and 12.5 UT (mag 20.2-22.0 given) but reported to the Minor Planet Center after the discovery observations above. The following orbital elements by S. Nakano (Central Bureau) are from 77 observations spanning 2025 Dec. 11-31 (mean residual 0".5). The comet passed 2.83 AU from Jupiter on 2025 Aug. 21 UT. The formal uncertainty in the period is +/- 3.2 years. T = 2026 Dec. 6.09451 TT Peri. = 84.77909 e = 0.8569275 Node = 95.64285 2000.0 q = 4.6967175 AU Incl. = 36.96012 a = 32.8275385 AU n = 0.00524018 P = 188.1 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 12 31 10 18.20 +41 16.5 4.605 5.305 131.3 8.0 19.6 2026 01 10 10 17.58 +42 36.5 4.495 5.273 138.5 7.1 19.5 2026 01 20 10 15.51 +43 55.7 4.410 5.241 144.3 6.3 19.5 2026 01 30 10 12.14 +45 10.0 4.351 5.210 147.6 5.8 19.4 2026 02 09 10 07.79 +46 15.4 4.319 5.179 147.6 5.9 19.4 2026 02 19 10 02.84 +47 08.4 4.314 5.150 144.3 6.4 19.4 2026 03 01 09 57.83 +47 46.5 4.334 5.121 138.7 7.3 19.4 2026 03 11 09 53.28 +48 08.7 4.377 5.093 131.8 8.4 19.4 2026 03 21 09 49.68 +48 15.1 4.439 5.065 124.1 9.4 19.4 2026 03 31 09 47.40 +48 06.8 4.517 5.039 116.2 10.2 19.4 2026 04 10 09 46.68 +47 45.7 4.607 5.013 108.3 10.9 19.4 2026 04 20 09 47.62 +47 13.8 4.706 4.988 100.5 11.4 19.4 2026 04 30 09 50.23 +46 33.0 4.809 4.964 93.0 11.7 19.5 2026 05 10 09 54.40 +45 45.1 4.915 4.942 85.6 11.8 19.5 2026 05 20 10 00.00 +44 51.4 5.019 4.919 78.6 11.6 19.5 2026 05 30 10 06.88 +43 53.2 5.119 4.898 71.8 11.3 19.6 2026 06 09 10 14.86 +42 51.4 5.214 4.878 65.4 10.9 19.6 2026 06 19 10 23.79 +41 46.7 5.301 4.859 59.2 10.3 19.6 2026 06 29 10 33.53 +40 39.9 5.379 4.841 53.4 9.7 19.6 2026 07 09 10 43.92 +39 31.5 5.446 4.824 47.9 9.0 19.6 2026 07 19 10 54.86 +38 22.0 5.503 4.808 42.9 8.3 19.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 January 7 (CBET 5650) Daniel W. E. Green