Electronic Telegram No. 5720 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 M5 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on June 22 (discovery observations tabulated below, together with earlier Pan-STARRS2 identified later by Weryk). Stacked images taken in 0".8 seeing on June 22 show a condensed coma of size 1".8 (full-width-at-half-maximum) with a straight 4"-long tail toward p.a. 40 degrees. The June 14 images were taken in poor conditions. (Note that the designation P/2026 M4 was assigned to the recovery of comet P/2006 HR_30; cf. CBET 5708). 2025 UT R.A. (2000) Decl. Mag. Sept.18.38657 23 44 54.17 +40 09 37.3 22.5 18.40726 23 44 52.42 +40 09 28.8 21.9 2026 UT R.A. (2000) Decl. Mag. June 14.54889 22 50 52.72 +19 45 10.0 21.0 14.56092 22 50 52.30 +19 45 09.9 20.8 14.57301 22 50 51.95 +19 45 09.7 21.0 14.58507 22 50 51.56 +19 45 09.5 21.1 22.52041 22 46 10.68 +19 39 36.1 21.5 22.53259 22 46 10.19 +19 39 35.3 21.9 22.54478 22 46 09.68 +19 39 34.5 21.3 22.55709 22 46 09.19 +19 39 33.8 21.6 Weryk also identified the comet in three Pan-STARRS1 exposures taken on 2025 Sept. 30.34-30.36 UT (at mag 22.0-22.7). Three 60-s gri-band follow-up images obtained by Weryk and R. Wainscoat with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea on 2026 July 8.6 (queue observer L. Wells; queue coordinator H. Flewelling) in 0".6 seeing show a very condensed coma of size 1".1 (FWHM) and a 6" tail in p.a. 50 degrees. Additional follow-up observations were obtained by Y. Ramanjooloo on July 22.44-22.46 with the University of Hawaii's 2.2-m telescope in 1".1 seeing, whereby two 180-s exposures were taken that show a condensed coma of size 1".9 (FWHM) with a straight tail about 6" long toward p.a. 60 degrees; the magnitude was measured to be 21.7-22.4. Weryk accidentally re-discovered this comet on images obtained with the Pan-STARRS2 telescope on 2026 July 25.45-25.47 at mag 21.2-21.8; four stacked 45-s w-band survey images taken in 1".1-1".2 seeing show a condensed coma of size 1".6 (FWHM) and a likely tail 4" long in p.a. around 50 degrees. Twenty stacked 60-s CCD exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph at Siding Spring, NSW, Australia, on 2026 June 23.8 UT show only a stellar appearance; the magnitude was 21.2 as measured within a circular aperture of radius 4".3. The comet also appeared stellar in thirty-two stacked 60-s CCD exposures taken by Sato on June 25.4 with a 0.51-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA); the magnitude was 20.9 as measured within a circular aperture of radius 4".9. The available astrometry appears on MPEC 2026-P39. The following orbital elements by S. Nakano (Central Bureau) are from 48 observations spanning 2025 Sept. 18-2026 Aug. 6 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.013349 and +0.013424 (+/- 0.000011) AU**-1, respectively. There are no close approaches to major planets. Epoch = 2026 Oct. 7.0 TT T = 2026 Oct. 8.65603 TT Peri. = 144.26559 e = 0.9359417 Node = 114.49989 2000.0 q = 4.9836485 AU Incl. = 147.45500 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 07 19 22 22.68 +18 20.7 4.354 5.021 126.1 9.4 20.3 2026 07 29 22 10.91 +17 19.5 4.228 5.012 136.3 8.0 20.2 2026 08 08 21 58.02 +15 59.0 4.135 5.005 145.6 6.6 20.2 2026 08 18 21 44.53 +14 19.7 4.080 4.999 152.4 5.4 20.1 2026 08 28 21 31.05 +12 24.6 4.066 4.993 154.0 5.1 20.1 2026 09 07 21 18.20 +10 18.7 4.095 4.989 149.5 5.9 20.1 2026 09 17 21 06.52 +08 07.6 4.165 4.986 141.0 7.3 20.2 2026 09 27 20 56.40 +05 57.2 4.272 4.984 130.8 8.8 20.2 2026 10 07 20 48.06 +03 52.6 4.409 4.984 119.9 10.0 20.3 2026 10 17 20 41.58 +01 57.2 4.571 4.984 108.9 10.9 20.4 2026 10 27 20 36.91 +00 13.0 4.748 4.986 98.1 11.4 20.5 2026 11 06 20 33.90 -01 19.0 4.933 4.988 87.4 11.5 20.5 2026 11 16 20 32.40 -02 38.9 5.120 4.992 77.1 11.1 20.6 2026 11 26 20 32.20 -03 47.2 5.301 4.997 66.9 10.5 20.7 2026 12 06 20 33.10 -04 45.0 5.470 5.003 57.0 9.5 20.8 2026 12 16 20 34.89 -05 33.1 5.624 5.010 47.4 8.3 20.8 2026 12 26 20 37.40 -06 12.9 5.757 5.018 37.9 6.9 20.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 August 7 (CBET 5720) Daniel W. E. Green