Electronic Telegram No. 5540 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/2010 LH_155 Y. Ramanjooloo, University of Hawaii, reported that he found a comet on four 45-s w-band exposures taken in 1".3-1".4 seeing on 2024 Dec. 31 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala; coma was condensed but extended (size 2".0 full-width-at-half-maximum) with a straight 3"-long tail in p.a. 290 degrees. R. Weryk, Department of Physics and Astronomy, University of Western Ontario, then linked Ramanjooloo's object to other Pan-STARRS1 observations already in the Minor Planet Center's "isolated tracklet file" (ITF) from 2024 Nov. 27 and Dec. 27 (under three separate preliminary designations). Weryk could not discern cometary activity in the Nov. 27 images, but seven 45-s w-band survey images taken in 1".3-1".4 seeing on 2024 Dec. 27 show a very condensed head of size 1".6 (FWHM) with a tail about 1" long in p.a. 300 degrees. The initial Pan-STARRS1 astrometry is tabulated below. 2024 UT R.A. (2000) Decl. Mag. Nov. 27.60749 9 53 26.65 + 2 08 00.3 21.9 27.62030 9 53 27.40 + 2 07 53.1 22.0 27.63318 9 53 28.15 + 2 07 45.9 21.7 Dec. 27.61739 10 15 26.20 - 2 09 42.7 20.8 27.61803 10 15 26.22 - 2 09 43.1 20.7 27.62792 10 15 26.45 - 2 09 47.4 20.9 27.63841 10 15 26.69 - 2 09 51.8 20.7 27.63905 10 15 26.71 - 2 09 52.1 20.7 27.64890 10 15 26.95 - 2 09 56.3 20.7 27.64954 10 15 26.97 - 2 09 56.6 20.8 31.59513 10 16 56.28 - 2 37 04.0 20.5 31.60719 10 16 56.50 - 2 37 08.7 20.6 31.61923 10 16 56.71 - 2 37 13.5 20.6 31.63128 10 16 56.92 - 2 37 18.3 20.4 From an orbit computed with the above Pan-STARRS1 astrometry, Weryk linked the 2024 observations to a single-night ITF object from 2018 May 5 that was imaged with a 2.6-m f/5.5 Ritchey-Chretien reflector at Cerro Paranal in Chile, and also with 2010 LH_155, a presumed asteroidal object with only a one-day arc of observations (and no published orbit) in 2010 that had been found with the Wide-field Infrared Survey Explorer earth-orbiting satellite (formerly known WISE; cf. CBET 4225). The minor-planet designation 2010 LH_155 was announced on MPS 924597 as late as 2018 Oct. 17. Weryk then identified further Pan-STARRS1 images of this object on 2018 May 19 and 20 UT, noting that the image quality on those two nights was too poor to tell if the object was active then. The 2018 and 2024 observations were posted initially on the MPC's PCCP webpage (evidently before the 2010 linkage was made); a three-opposition orbit for 2010 LH_155 appeared on MPO 885003 (2025 Jan. 15). The initial linked observations are tabulated below. 2010 UT R.A. (2000) Decl. June 14.70504 11 53 14.71 - 2 47 15.6 14.96964 11 53 31.82 - 2 48 01.3 15.10195 11 53 40.51 - 2 48 26.3 15.23425 11 53 49.19 - 2 48 51.3 15.69725 11 54 19.44 - 2 50 15.0 15.82956 11 54 27.89 - 2 50 39.5 2018 UT R.A. (2000) Decl. Mag. May 5.30580 15 19 13.24 -16 49 05.8 21.2 5.30700 15 19 13.18 -16 49 05.3 21.2 5.31169 15 19 12.98 -16 49 03.6 21.5 5.31290 15 19 12.92 -16 49 03.2 21.5 5.31874 15 19 12.66 -16 49 01.1 21.3 5.31995 15 19 12.61 -16 49 00.6 21.2 19.42618 15 09 13.99 -15 26 05.5 22.0 19.43807 15 09 13.49 -15 26 01.4 21.8 19.44999 15 09 13.01 -15 25 57.5 22.0 19.46189 15 09 12.48 -15 25 53.3 21.7 20.46092 15 08 32.81 -15 20 21.4 20.1 20.47234 15 08 32.25 -15 20 17.6 21.2 Fourteen stacked 60-s CCD exposures taken remotely on 2025 Jan. 25.7 UT by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, show a strongly condensed coma 8" in diameter with a 20"-long tail in p.a. 320 degrees; the magnitude was 18.8 as measured within a circular aperture of radius 4".9. Additional astrometry appears on MPEC 2025-H69, though unfortunately without the customary 2018 and 2024 discovery provisional comet designations. The following linked orbital elements by S. Nakano (Central Bureau) are from 242 observations spanning 2010 June 14-2025 Apr. 15 (mean residual 0".4). The comet passed 0.80 and 0.96 AU from Jupiter on 1998 Feb. 19 and 2023 Mar. 20 UT, respectively. Epoch = 2002 July 25.0 TT T = 2002 July 5.43578 TT Peri. = 304.65941 e = 0.3862947 Node = 222.93805 2000.0 q = 2.3735703 AU Incl. = 8.34311 a = 3.8676057 AU n = 0.12958084 P = 7.61 years Epoch = 2010 Feb. 13.0 TT T = 2010 Feb. 18.00806 TT Peri. = 304.76196 e = 0.3847170 Node = 222.87593 2000.0 q = 2.3859299 AU Incl. = 8.33704 a = 3.8777762 AU n = 0.12907138 P = 7.64 years Epoch = 2017 Oct. 14.0 TT T = 2017 Sept.30.44243 TT Peri. = 304.76643 e = 0.3864421 Node = 222.83103 2000.0 q = 2.3721467 AU Incl. = 8.34933 a = 3.8662150 AU n = 0.12965076 P = 7.60 years Epoch = 2025 Mar. 26.0 TT T = 2025 Apr. 9.00756 TT Peri. = 308.51807 e = 0.4059777 Node = 221.11908 2000.0 q = 2.2240464 AU Incl. = 8.80684 a = 3.7440455 AU n = 0.13604807 P = 7.24 years Epoch = 2032 July 27.0 TT T = 2032 July 13.80365 TT Peri. = 308.73542 e = 0.4047867 Node = 221.03372 2000.0 q = 2.2311738 AU Incl. = 8.80579 a = 3.7485282 AU n = 0.13580411 P = 7.26 years Epoch = 2039 Oct. 19.0 TT T = 2039 Oct. 11.96803 TT Peri. = 308.63224 e = 0.4050811 Node = 220.96426 2000.0 q = 2.2307807 AU Incl. = 8.80820 a = 3.7497224 AU n = 0.13573924 P = 7.26 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 11.5 and 2.5n = 15 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 03 26 09 50.85 +00 07.0 1.348 2.226 142.9 15.7 17.4 2025 04 05 09 51.88 +01 10.2 1.413 2.224 133.6 19.0 17.5 2025 04 15 09 55.77 +01 59.9 1.494 2.224 124.8 21.7 17.6 2025 04 25 10 02.31 +02 33.4 1.586 2.227 116.7 23.8 17.7 2025 05 05 10 11.19 +02 49.5 1.688 2.232 109.1 25.3 17.9 2025 05 15 10 22.05 +02 48.5 1.798 2.240 102.1 26.2 18.0 2025 05 25 10 34.52 +02 31.6 1.913 2.249 95.6 26.6 18.2 2025 06 04 10 48.30 +02 00.2 2.032 2.262 89.4 26.6 18.4 2025 06 14 11 03.10 +01 15.9 2.153 2.276 83.6 26.3 18.5 2025 06 24 11 18.69 +00 20.8 2.277 2.292 78.0 25.7 18.7 2025 07 04 11 34.91 -00 43.7 2.401 2.311 72.6 24.8 18.9 2025 07 14 11 51.61 -01 55.6 2.525 2.331 67.4 23.7 19.0 2025 07 24 12 08.68 -03 13.2 2.647 2.353 62.3 22.5 19.2 2025 08 03 12 26.06 -04 35.0 2.768 2.377 57.2 21.0 19.4 2025 08 13 12 43.68 -05 59.3 2.886 2.403 52.2 19.5 19.5 2025 08 23 13 01.50 -07 24.9 3.001 2.430 47.2 17.8 19.7 2025 09 02 13 19.49 -08 50.3 3.111 2.459 42.2 16.0 19.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 April 24 (CBET 5540) Daniel W. E. Green