Electronic Telegram No. 5551 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/2017 FL_36 (PANSTARRS) An apparently asteroidal object discovered in March 2017 on images taken with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii, was found later to show cometary appearance after it was given the minor- planet designation 2017 FL_36 on MPS 779056. The discovery observations are tabulated below. 2017 UT R.A. (2000) Decl. Mag. Mar. 18.39009 10 12 48.51 - 1 08 38.8 21.5 18.40331 10 12 47.88 - 1 08 37.3 21.2 18.41650 10 12 47.28 - 1 08 35.7 21.2 18.42973 10 12 46.68 - 1 08 34.2 21.1 On 2024 May 29, K. Ly (University of California at Los Angeles) wrote that he found a single 174-s g-band DECam exposure taken by D. Lang, R. Zhou, and A. Walker with the 4-m reflector at Cerro Tololo Interamerican Observatory on 2017 Mar. 1.19 UT, showing that this main-belt asteroid then had a very condensed coma about 2" in diameter with total g-band magnitude 20.8, and no signs of a tail (though the coma appears to be slightly elongated northward). Following a request from the Central Bureau to look closely at the discovery images, R. Weryk (Department of Physics and Astronomy, University of Western Ontario) reports that four 45-s i-band Pan-STARRS1 images taken on 2017 Mar. 18 in variable (0".7-0".8) seeing show no tail but a head of size 1".2-1".3. The cometary nature appears "much more obvious" (coma size 1".4 FWHM) in four 45-s w-band images taken on 2017 Feb. 25 in 1".2-1".3 seeing. Pre-discovery single-night observations were subsequently identified in the Minor Planet Center's "isolated tracklet file" from 2017 Feb. 23.4 UT (Mt. Lemmon 1.5-m reflector, mag 19.6-20.9) and 2017 Feb. 25.44-25.47 (Pan-STARRS1, mag 20.5-20.7). S. Urakawa (Japan Spaceguard Association) reported to the MPC that 8.2-m Subaru Telescope observations from 2017 Mar. 21, 29, and Apr. 1 show a coma of size 1"-1".4 and a tail 4"-9" long in p.a. 23-35 deg (cf. MPEC 2025-H86). The following perturbed orbital elements by S. Nakano (Central Bureau) are from 27 observations spanning 2017 Feb. 23-Apr. 1 (mean residual 0".4). There are no close approaches to major planets. Nakano was unable to identify this comet in archival astrometry from 2020. Epoch = 2000 June 25.0 TT T = 2000 July 5.93549 TT Peri. = 87.42308 e = 0.0368160 Node = 313.88648 2000.0 q = 2.8223724 AU Incl. = 15.67058 a = 2.9302527 AU n = 0.19649272 P = 5.02 years Epoch = 2005 July 9.0 TT T = 2005 June 19.77478 TT Peri. = 83.48750 e = 0.0363919 Node = 313.75929 2000.0 q = 2.8215508 AU Incl. = 15.69029 a = 2.9281103 AU n = 0.19670841 P = 5.01 years Epoch = 2010 June 13.0 TT T = 2010 June 14.73648 TT Peri. = 81.54661 e = 0.0327337 Node = 313.69834 2000.0 q = 2.8314703 AU Incl. = 15.69086 a = 2.9272914 AU n = 0.19679095 P = 5.01 years Epoch = 2015 June 27.0 TT T = 2015 June 27.29651 TT Peri. = 83.23829 e = 0.0313729 Node = 313.66482 2000.0 q = 2.8360097 AU Incl. = 15.68806 a = 2.9278653 AU n = 0.19673310 P = 5.01 years Epoch = 2020 July 10.0 TT T = 2020 July 24.33348 TT Peri. = 88.03132 e = 0.0314010 Node = 313.47854 2000.0 q = 2.8357063 AU Incl. = 15.68560 a = 2.9276369 AU n = 0.19675612 P = 5.01 years Epoch = 2025 July 24.0 TT T = 2025 Aug. 7.55281 TT Peri. = 89.99792 e = 0.0325301 Node = 313.44981 2000.0 q = 2.8318221 AU Incl. = 15.68682 a = 2.9270390 AU n = 0.19681642 P = 5.01 years Epoch = 2030 Aug. 7.0 TT T = 2030 Aug. 6.67200 TT Peri. = 88.92972 e = 0.0357017 Node = 313.39981 2000.0 q = 2.8238779 AU Incl. = 15.68095 a = 2.9284276 AU n = 0.19667644 P = 5.01 years Epoch = 2035 July 12.0 TT T = 2035 July 21.88021 TT Peri. = 85.10256 e = 0.0368133 Node = 313.29352 2000.0 q = 2.8230793 AU Incl. = 15.66281 a = 2.9309784 AU n = 0.19641975 P = 5.02 years Epoch = 2040 July 25.0 TT T = 2040 July 10.84563 TT Peri. = 82.37033 e = 0.0351948 Node = 313.18529 2000.0 q = 2.8253811 AU Incl. = 15.67201 a = 2.9284471 AU n = 0.19667447 P = 5.01 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 07 24 03 34.38 +33 41.1 3.153 2.832 62.5 18.6 21.0 2025 08 03 03 48.48 +34 57.7 3.038 2.832 68.7 19.5 20.9 2025 08 13 04 01.72 +36 10.8 2.918 2.832 75.1 20.2 20.8 2025 08 23 04 13.86 +37 20.7 2.794 2.832 81.8 20.7 20.8 2025 09 02 04 24.58 +38 27.7 2.668 2.832 88.8 20.9 20.7 2025 09 12 04 33.52 +39 31.9 2.542 2.833 96.2 20.7 20.5 2025 09 22 04 40.31 +40 33.3 2.418 2.833 104.0 20.1 20.4 2025 10 02 04 44.50 +41 31.0 2.300 2.834 112.2 19.1 20.3 2025 10 12 04 45.72 +42 23.0 2.190 2.834 120.9 17.6 20.2 2025 10 22 04 43.66 +43 06.4 2.092 2.835 129.9 15.6 20.1 2025 11 01 04 38.29 +43 36.5 2.010 2.836 139.1 13.2 20.0 2025 11 11 04 29.97 +43 48.0 1.949 2.837 147.9 10.7 20.0 2025 11 21 04 19.54 +43 36.4 1.911 2.838 155.2 8.4 19.9 2025 12 01 04 08.31 +42 59.9 1.900 2.840 158.4 7.4 19.9 2025 12 11 03 57.77 +42 00.8 1.915 2.841 155.5 8.3 19.9 2025 12 21 03 49.20 +40 45.3 1.958 2.843 148.4 10.5 20.0 2025 12 31 03 43.47 +39 21.9 2.025 2.844 139.4 13.0 20.1 2026 01 10 03 40.95 +37 58.7 2.113 2.846 130.0 15.4 20.2 2026 01 20 03 41.61 +36 41.3 2.218 2.848 120.6 17.3 20.3 2026 01 30 03 45.22 +35 33.5 2.337 2.850 111.5 18.8 20.4 2026 02 09 03 51.43 +34 36.3 2.465 2.852 102.9 19.7 20.5 2026 02 19 03 59.86 +33 49.3 2.598 2.854 94.6 20.2 20.6 2026 03 01 04 10.19 +33 11.1 2.734 2.856 86.8 20.3 20.7 2026 03 11 04 22.08 +32 39.8 2.870 2.858 79.3 20.0 20.9 2026 03 21 04 35.28 +32 13.3 3.004 2.861 72.2 19.4 21.0 2026 03 31 04 49.56 +31 49.7 3.132 2.863 65.3 18.5 21.0 2026 04 10 05 04.71 +31 27.2 3.255 2.866 58.7 17.4 21.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 April 30 (CBET 5551) Daniel W. E. Green