Electronic Telegram No. 5457 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 P/2024 S2 (RANKIN) David Rankin, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a diffuse comet with a condensed 12" coma and no tail on CCD images obtained on Sept. 30 with a 0.28-m f/2.2 reflector at his home observatory (not part of the Catalina Sky Survey). The discovery observations are tabulated below. 2024 UT R.A. (2000) Decl. Mag. Observer Sept.30.42226 6 11 41.90 +30 49 33.9 17.6 Rankin 30.44579 6 11 44.30 +30 49 41.1 17.6 " 30.46795 6 11 46.60 +30 49 45.8 17.7 " After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists elsewhere commented on the cometary appearance. Sixteen stacked 60-s exposures taken on Oct. 2.5 UT remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show a strongly condensed coma 12" in diameter with no tail; the magnitude was 18.2 as measured within a circular aperture of radius 7".6. D. D. Balam, Dominion Astrophysical Observatory (DAO), reports that thirty-one 60-s exposures taken on Oct. 2.52 with the 1.82-m Plaskett telescope at DAO (National Research Council of Canada) by Balam (in collaboration with C. E. Spratt, E. Hess, and D. W. E. Green) in 4".1 seeing show a coma of size 5".6 through an SDSS g' filter. The available astrometry appears on MPEC 2024-T259. The following two-body elliptical orbital elements by S. Nakano (Central Bureau) are from 142 observations spanning Sept. 30-Oct. 10 (mean residual 0".5). The orbital period is uncertain by a third of a year (formal error). There are no close approaches to major planets. T = 2024 Sept.15.99203 TT Peri. = 48.94159 e = 0.6019088 Node = 8.46113 2000.0 q = 2.0500389 AU Incl. = 7.53354 a = 5.1496721 AU n = 0.08434022 P = 11.7 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.5 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 09 07 05 26.20 +28 52.8 1.933 2.052 82.0 29.1 18.1 2024 09 17 05 46.54 +29 46.9 1.836 2.050 87.2 29.3 17.9 2024 09 27 06 05.57 +30 34.5 1.743 2.053 92.8 29.2 17.8 2024 10 07 06 22.81 +31 17.4 1.653 2.059 98.9 28.7 17.7 2024 10 17 06 37.79 +31 58.1 1.568 2.070 105.5 27.6 17.6 2024 10 27 06 50.04 +32 38.8 1.489 2.085 112.7 26.1 17.6 2024 11 06 06 59.01 +33 21.1 1.418 2.104 120.6 23.9 17.5 2024 11 16 07 04.30 +34 05.2 1.358 2.127 129.3 21.1 17.4 2024 11 26 07 05.68 +34 49.5 1.311 2.153 138.6 17.6 17.4 2024 12 06 07 03.20 +35 30.0 1.281 2.182 148.4 13.7 17.4 2024 12 16 06 57.51 +36 00.8 1.271 2.215 158.0 9.6 17.5 2024 12 26 06 49.79 +36 16.4 1.285 2.251 165.5 6.3 17.6 2025 01 05 06 41.59 +36 13.5 1.323 2.289 165.6 6.1 17.7 2025 01 15 06 34.55 +35 52.9 1.386 2.329 158.5 8.9 17.9 2025 01 25 06 29.84 +35 18.4 1.473 2.372 149.1 12.3 18.1 2025 02 04 06 28.11 +34 35.1 1.582 2.417 139.5 15.4 18.3 2025 02 14 06 29.51 +33 47.2 1.708 2.464 130.2 17.8 18.6 2025 02 24 06 33.79 +32 57.6 1.851 2.512 121.4 19.6 18.8 2025 03 06 06 40.59 +32 07.7 2.006 2.562 113.1 20.9 19.1 2025 03 16 06 49.47 +31 17.7 2.170 2.613 105.2 21.5 19.4 2025 03 26 06 59.99 +30 27.3 2.342 2.666 97.7 21.8 19.6 2025 04 05 07 11.81 +29 35.8 2.518 2.719 90.6 21.6 19.8 2025 04 15 07 24.59 +28 42.7 2.698 2.773 83.7 21.1 20.1 2025 04 25 07 38.06 +27 47.3 2.878 2.828 77.1 20.3 20.3 2025 05 05 07 52.00 +26 49.3 3.056 2.883 70.6 19.3 20.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 October 12 (CBET 5457) Daniel W. E. Green