Electronic Telegram No. 5491 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/2024 PN_7 (PANSTARRS) An apparently asteroidal object discovered in images obtained on 2024 Aug. 15 with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below) has been found to show cometary activity by astrometrists elsewhere. It was put on the Minor Planet Center's NEOCP webpage (and also its PCCP webpage for a time) before being announced on 2024 Sept. 5 with the minor-planet designation 2024 PN_7 (MPEC 2024-Q29). 2024 UT R.A. (2000) Decl. Mag. Aug. 15.44264 0 55 51.14 +20 17 04.5 20.0 15.46248 0 55 48.33 +20 17 42.5 19.8 15.47240 0 55 46.93 +20 18 01.6 19.9 15.52943 0 55 38.81 +20 19 50.9 19.9 15.52944 0 55 38.80 +20 19 51.0 20.1 15.53008 0 55 38.72 +20 19 52.2 19.9 A. Hale (Cloudcroft, NM, USA) reported that 180-s CCD exposures obtained remotely on Oct. 30.9 UT with a 0.35-m f/3 Cassegrain reflector at Tenerife show a somewhat condensed object with a slightly diffuse coma of size 5"; 300-s exposures with the same telescope on 2024 Oct. 31.9 show no obvious coma, although the object appears to be marginally more diffuse than stars of similar brightness. Further images taken remotely on Nov. 1.83 by Hale with a 1.0-m f/8 Schmidt-Cassegrain reflector at Tenerife show a condensed central region surrounded by small, faint, 5" diffuse coma; the condensed region was somewhat off-center towards the coma's western side, creating the appearance of the beginning of a short eastward-pointing tail. H. Sato (Bunkyo-ku, Tokyo, Japan) obtained twenty-four stacked 30-s CCD exposures with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) on 2024 Aug. 29.47 UT that show a completely stellar appearance; the magnitude was 19.4 as measured within a circular aperture of radius 5".7. The object was apparently placed back on the PCCP webpage as a result of Hale's report, after which Sato obtained thirteen more stacked 60-s exposures on 2024 Nov. 9.1 (same telescope as above) that showed now a strongly condensed coma 8" in diameter with no tail; the magnitude was again 19.4 as measured within a circular aperture of radius 5".7. Sato further obtained fifteen stacked 60-s CCD exposures on Nov. 4.15- 4.16 with a 0.61-m f/6.5 astrograph located at the Sierra Remote Observatory near Auberry, CA, USA, that show a strongly condensed coma 7" in diameter with no tail; the magnitude was 19.1 as measured within a circular aperture of radius 3".8. L. Buzzi, Varese, Italy, writes that he obtained sixty 60-s stacked CMOS exposures on 2024 Nov. 2.75-2.77 UT (measured by Buzzi and A. Aletti) with a 0.84-m f/3.5 reflector as a result of Hale's posting about cometary appearance of 2024 PN_7 on the comets-ml discussion group; the stacked images show a very condensed coma 4" wide, faintly but clearly elongated toward p.a. 45 degrees. Two-hundred-thirty-nine additional stacked 30-s CCD exposures obtained by Aletti (and measured by Aletti and M. Auteri) with a 0.36-m f/7.5 reflector on Nov. 22.74-22.79 show a condensed coma 5" wide that was slightly extended toward the northeast (only slightly larger than stars of similar brightness (5".9 vs. 4".6 full-width-at-half-maximum); the comet's magnitude was measured as 18.2-18.3. CMOS images taken on 2024 Nov. 6.4 by K. Yoshimoto (Kumage, Yamaguchi, Japan) with a 0.20-m f/8 Ritchey-Chretien relector show the suggestions of a faint coma of total mag 18.7. Thirty-nine stacked 60-s follow-up images taken by Yoshimoto on Nov. 21.4 show the object to be definitely cometary with a condensed, diffuse coma 14" in diameter, with diffuseness extending from south to east; the total mag was 17.7. The available astrometry appears on MPEC 2024-A145. The following orbital elements by S. Nakano (Central Bureau) are from 227 observations spanning 2024 Aug. 15-Nov. 27 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.015635 and +0.015759 (+/- 0.000023) AU**-1, respectively. The indicated orbital period is 553.6 years. The comet passed 3.89 AU from Jupiter on 2023 Dec. 24 UT. Epoch = 2024 Nov. 26.0 TT T = 2024 Dec. 6.43784 TT Peri. = 74.27247 e = 0.9773867 Node = 358.58218 2000.0 q = 1.5245338 AU Incl. = 101.21065 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 16.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 12 16 18 16.16 +25 44.9 1.963 1.530 50.1 29.6 18.9 2024 12 26 18 13.78 +26 19.7 1.990 1.548 49.7 29.0 19.0 2025 01 05 18 11.34 +27 24.0 1.988 1.578 51.6 29.2 19.1 2025 01 15 18 08.15 +28 59.9 1.957 1.618 55.5 30.1 19.1 2025 01 25 18 03.39 +31 10.5 1.902 1.668 61.2 31.1 19.2 2025 02 04 17 55.98 +34 00.0 1.828 1.727 68.3 32.0 19.2 2025 02 14 17 44.27 +37 30.8 1.742 1.793 76.6 32.4 19.2 2025 02 24 17 25.92 +41 40.5 1.654 1.865 85.9 31.9 19.3 2025 03 06 16 57.45 +46 14.3 1.576 1.943 95.6 30.5 19.3 2025 03 16 16 14.78 +50 31.5 1.521 2.025 105.3 28.3 19.4 2025 03 26 15 16.50 +53 20.5 1.505 2.110 113.4 25.7 19.5 2025 04 05 14 09.98 +53 28.0 1.537 2.199 118.6 23.6 19.7 2025 04 15 13 10.05 +50 45.0 1.623 2.289 119.4 22.4 19.9 2025 04 25 12 25.69 +46 15.7 1.760 2.382 116.2 22.3 20.2 2025 05 05 11 56.36 +41 12.2 1.938 2.476 110.3 22.5 20.6 2025 05 15 11 38.14 +36 18.3 2.149 2.570 102.9 22.5 20.9 2025 05 25 11 27.45 +31 51.2 2.381 2.666 94.9 22.2 21.3 2025 06 04 11 21.84 +27 54.1 2.627 2.762 86.8 21.5 21.6 2025 06 14 11 19.69 +24 24.6 2.880 2.859 78.7 20.4 21.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 January 9 (CBET 5491) Daniel W. E. Green