Electronic Telegram No. 5677 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/2026 A3 (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, whose cometary appearance was only noticed after P. Veres (Minor Planet Center) asked Weryk to look at images after Veres found multiple nights of an object showing a cometary orbit in the MPC's "isolated tracklet file", with Veres posting it to the MPC's PCCP webpage. In the four 45-s w-band discovery observations (tabulated below), obtained in 1".2-1".3 seeing, Weryk noted (from two stacked images) that the head showed a size of 1".6 (full-width-at-half- maximum) with no tail. 2026 UT R.A. (2000) Decl. Mag. Jan. 13.42144 9 15 55.21 +18 38 17.6 21.4 13.43470 9 15 54.45 +18 38 19.7 21.3 13.44807 9 15 53.69 +18 38 21.8 21.6 Three stacked 60-s gri-band follow-up observations obtained by Weryk and R. Wainscoat with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea on Mar. 25.3 UT (queue observer J. Silva; queue coordinator H. Flewelling) in 0".8 seeing show a very condensed head of size 1".7 (FWHM) and a clear tail 14" long toward p.a. 85 degrees. After the comet was posted to the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that nineteen stacked 60-s CCD exposures obtained remotely with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, on Mar. 23.44 UT show only a stellar appearance; the magnitude was 20.8 as measured within a circular aperture of radius 4".9. The available astrometry appears on 2026-F279 and includes pre-discovery observations obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on 2025 Nov. 29 (mag 21.3-21.8) and 2025 Dec. 29 (mag 20.8-21.8). The following orbital elements by S. Nakano (Central Bureau) are rom 62 observations spanning 2025 Nov. 29-2026 Mar. 26 (mean residual 0".3), with corresponding "original" and "future" values of 1/a being +0.000104 and -0.000127 (+/- 0.000047) AU**-1, respectively. The comet passed 0.79 AU from Jupiter on 2026 June 21 UT. Epoch = 2027 Oct. 2.0 TT T = 2027 Sept.30.73772 TT Peri. = 239.10044 e = 1.0023410 Node = 307.00525 2000.0 q = 4.8050825 AU Incl. = 157.43282 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 02 09 08 48.54 +19 44.1 5.645 6.616 169.2 1.6 20.3 2026 02 19 08 38.01 +20 03.6 5.648 6.567 156.7 3.4 20.3 2026 03 01 08 28.01 +20 18.5 5.688 6.518 144.3 5.1 20.3 2026 03 11 08 18.90 +20 28.4 5.761 6.470 132.2 6.5 20.3 2026 03 21 08 10.93 +20 33.4 5.860 6.422 120.4 7.7 20.3 2026 03 31 08 04.27 +20 33.8 5.979 6.374 109.0 8.5 20.3 2026 04 10 07 58.98 +20 30.2 6.110 6.327 97.9 9.0 20.3 2026 04 20 07 55.04 +20 23.2 6.247 6.280 87.2 9.2 20.4 2026 04 30 07 52.37 +20 13.2 6.383 6.233 76.9 9.1 20.4 2026 05 10 07 50.84 +20 00.7 6.513 6.187 66.9 8.6 20.4 2026 05 20 07 50.34 +19 46.1 6.630 6.141 57.2 8.0 20.4 2026 05 30 07 50.70 +19 29.4 6.731 6.096 47.7 7.1 20.4 2026 06 09 07 51.79 +19 11.0 6.812 6.051 38.5 6.0 20.4 2026 09 17 08 12.61 +14 56.9 6.193 5.629 51.9 8.1 20.0 2026 09 27 08 12.61 +14 28.5 5.998 5.590 61.6 9.1 19.9 2026 10 07 08 11.57 +14 00.6 5.788 5.552 71.5 9.8 19.8 2026 10 17 08 09.30 +13 33.7 5.568 5.514 81.8 10.3 19.7 2026 10 27 08 05.59 +13 08.2 5.344 5.477 92.5 10.4 19.5 2026 11 06 08 00.24 +12 44.4 5.123 5.441 103.5 10.2 19.4 2026 11 16 07 53.09 +12 22.6 4.912 5.406 115.1 9.5 19.3 2026 11 26 07 44.04 +12 03.2 4.719 5.372 127.1 8.4 19.2 2026 12 06 07 33.12 +11 46.1 4.551 5.338 139.4 6.9 19.1 2026 12 16 07 20.50 +11 31.4 4.418 5.305 151.7 5.0 19.0 2026 12 26 07 06.56 +11 19.1 4.324 5.273 163.1 3.1 19.0 2027 01 05 06 51.84 +11 08.8 4.275 5.242 168.2 2.2 18.9 2027 01 15 06 37.01 +11 00.7 4.272 5.212 160.9 3.5 18.9 2027 01 25 06 22.78 +10 54.5 4.314 5.182 149.0 5.6 18.9 2027 02 04 06 09.73 +10 50.3 4.395 5.154 136.4 7.6 18.9 2027 02 14 05 58.31 +10 47.9 4.509 5.127 123.9 9.2 18.9 2027 02 24 05 48.75 +10 47.2 4.649 5.100 111.8 10.4 19.0 2027 03 06 05 41.12 +10 47.8 4.804 5.075 100.2 11.1 19.1 2027 03 16 05 35.36 +10 49.4 4.968 5.050 89.0 11.4 19.1 2027 03 26 05 31.30 +10 51.4 5.133 5.027 78.3 11.2 19.2 2027 04 05 05 28.77 +10 53.2 5.291 5.005 68.1 10.7 19.2 2027 04 15 05 27.54 +10 54.3 5.438 4.983 58.2 9.9 19.3 2027 04 25 05 27.41 +10 54.2 5.568 4.963 48.8 8.8 19.3 2027 08 03 05 46.85 +08 06.1 5.483 4.827 45.6 8.6 19.2 2027 08 13 05 47.27 +07 24.2 5.336 4.820 54.6 9.9 19.1 2027 08 23 05 46.72 +06 36.3 5.172 4.815 64.0 10.9 19.0 2027 09 02 05 44.96 +05 42.0 4.995 4.810 73.7 11.6 19.0 2027 09 12 05 41.76 +04 41.3 4.811 4.807 83.8 12.0 18.9 2027 09 22 05 36.90 +03 34.1 4.626 4.806 94.2 12.0 18.8 2027 10 02 05 30.17 +02 20.9 4.446 4.805 105.1 11.6 18.7 2027 10 12 05 21.39 +01 02.8 4.281 4.806 116.2 10.7 18.6 2027 10 22 05 10.51 -00 18.5 4.137 4.808 127.5 9.5 18.5 2027 11 01 04 57.64 -01 40.2 4.023 4.811 138.4 7.9 18.5 2027 11 11 04 43.08 -02 58.5 3.948 4.816 147.9 6.3 18.4 2027 11 21 04 27.38 -04 09.3 3.916 4.822 153.8 5.2 18.4 2027 12 01 04 11.24 -05 08.7 3.930 4.829 153.0 5.3 18.4 2027 12 11 03 55.47 -05 53.7 3.990 4.838 146.0 6.5 18.5 2027 12 21 03 40.77 -06 23.4 4.091 4.847 136.0 8.1 18.5 2027 12 31 03 27.72 -06 38.2 4.229 4.858 124.9 9.6 18.6 2028 01 10 03 16.64 -06 40.0 4.394 4.870 113.5 10.7 18.7 2028 01 20 03 07.65 -06 31.3 4.578 4.884 102.3 11.4 18.8 2028 01 30 03 00.70 -06 14.6 4.774 4.898 91.4 11.6 18.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 March 31 (CBET 5677) Daniel W. E. Green