Electronic Telegram No. 5191 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/2020 MK_4 (PANSTARRS) An apparently asteroidal object discovered on images images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii, on 2020 June 24 (discovery observations tabulated below along with some pre-discovery Pan-STARRS1 observations; cf. MPEC 2020-N36, where it was given the minor- planet designation 2020 MK_4) has been found later in 2020 to show cometary appearance by CCD astrometrists elsewhere and also by the Pan-STARRS1 team. 2020 UT R.A. (2000) Decl. Mag. June 15.53011 20 16 13.71 -27 05 45.3 21.1 15.56110 20 16 13.13 -27 05 47.9 21.4 20.53009 20 14 32.80 -27 13 26.6 20.4 20.54043 20 14 32.57 -27 13 27.6 20.6 20.55078 20 14 32.35 -27 13 28.7 20.8 20.56110 20 14 32.11 -27 13 29.6 20.4 24.50357 20 13 03.55 -27 19 36.7 19.8 24.51408 20 13 03.31 -27 19 37.5 19.9 24.52456 20 13 03.05 -27 19 38.6 19.9 H. Sato, Tokyo, Japan, writes that, while 2020 MK_4 appeared stellar on eight stacked 60-s CCD exposures taken remotely with a 0.51-m f/6.8 astrograph at Siding Spring Observatory on 2020 July 12.6 UT, a similar stack on 2020 Aug. 24.5 show a strongly condensed head with an outer coma 8" in diameter and no tail; on 2020 Sept. 8.4, nine stacked 60-s exposures show a strongly condensed and more obvious coma 12" diameter with no tail; the magnitude was 18.8 as measured within a circular aperture of radius 6".5. E. Guido, Castellammare di Stabia, Italy, reports that twenty stacked 180-s unfiltered exposures taken remotely by a large group of observers on 2020 Oct. 11.1 UT using a "Telescope Live" 0.6-m f/6.5 astrograph at El Sauce, Chile, show a diffuse coma about 7" in diameter elongated toward p.a. 150 degrees (mag 19.4-19.9). Following a request by the Central Bureau to look at the Pan-STARRS1 images, R. Weryk (Institute for Astronomy, University of Hawaii) writes that four 45-s w-band Pan-STARRS1 images taken on 2020 Aug. 22 show the comet's head to be very noticeably larger (2".3 full-width-at-half-maximum) than the images of nearby stars (FWHM 1".3), with no visible tail; he adds that conditions were not favorable for determining any possible activity in earlier Pan-STARRS images. Weryk adds that three 60-s gri-band follow-up observations obtained by R. Wainscoat, H. Januszewski, T. Burdullis, and himself with the Canada-France-Hawaii Telescope also show the comet's head to be larger than stellar profiles with no obvious tail. The following orbital elements by S. Nakano (CBAT) [which include three nights of observations in 2021 (mag given as 20-21) and two nights of observations in 2022 (mag 24.5 from the 4.3-m Lowell Discovery Telescope), published on MPEC 2022-W78] are from 149 observations spanning 2020 June 15- 2022 Oct. 29 (mean residual 0".5). The residuals for the 2022 observations were +41" in R.A. and +13" in Decl. from an orbit in HICQ 2021, with an indicated correction of Delta(T) = -0.19 day. The comet passed 3.85 AU from Saturn on 2020 Nov. 13 and 1.24 AU from Jupiter on 2020 Dec. 24 UT; due to the latter approach, the value of the argument of perihelion changed noticeably due to the small orbital eccentricity. There have been no close approaches to major planets, and Nakano was unable to find any additional earlier observations in archival data. Epoch = 2016 Sept. 9.0 TT T = 2016 Sept.18.30133 TT Peri. = 199.54417 e = 0.0433682 Node = 4.96322 2000.0 q = 6.0390160 AU Incl. = 6.69876 a = 6.3127902 AU n = 0.06214011 P = 15.86 years Epoch = 2027 June 4.0 TT T = 2027 June 17.42375 TT Peri. = 97.52478 e = 0.0161466 Node = 0.64841 2000.0 q = 6.1270803 AU Incl. = 6.78039 a = 6.2276355 AU n = 0.06341899 P = 15.54 years Epoch = 2043 Mar. 12.0 TT T = 2043 Feb. 24.67729 TT Peri. = 103.24221 e = 0.0156714 Node = 0.54051 2000.0 q = 6.0764254 AU Incl. = 6.79207 a = 6.1731678 AU n = 0.06426018 P = 15.34 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 9.0, 2.5n = 8.0 for the magnitudes, which are from the 2020 observations (when there may have been an outburst). Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 10 28 22 54.68 -08 38.3 5.581 6.234 127.4 7.3 19.1 2022 11 17 22 53.61 -08 29.7 5.869 6.233 107.2 8.7 19.2 2022 12 07 22 56.57 -07 57.4 6.191 6.232 87.8 9.1 19.3 2022 12 27 23 03.17 -07 03.8 6.509 6.230 69.3 8.5 19.4 2023 01 16 23 12.70 -05 52.7 6.792 6.229 51.6 7.1 19.5 2023 02 05 23 24.37 -04 28.5 7.015 6.227 34.5 5.1 19.6 2023 05 16 00 30.15 +03 20.8 6.874 6.220 46.3 6.8 19.5 2023 06 05 00 40.42 +04 35.8 6.618 6.218 62.7 8.3 19.5 2023 06 25 00 48.23 +05 35.7 6.318 6.216 79.6 9.3 19.4 2023 07 15 00 52.94 +06 16.6 6.002 6.215 97.4 9.3 19.2 2023 08 04 00 53.98 +06 35.7 5.699 6.213 116.1 8.4 19.1 2023 08 24 00 51.16 +06 31.5 5.444 6.211 136.0 6.5 19.0 2023 09 13 00 44.94 +06 05.8 5.271 6.210 156.9 3.6 19.0 2023 10 03 00 36.65 +05 25.7 5.208 6.208 178.1 0.3 18.9 2023 10 23 00 28.31 +04 42.7 5.265 6.206 159.3 3.2 18.9 2023 11 12 00 22.01 +04 10.0 5.437 6.204 137.7 6.2 19.0 2023 12 02 00 19.20 +03 57.4 5.696 6.203 116.8 8.2 19.1 2023 12 22 00 20.44 +04 09.5 6.007 6.201 96.8 9.1 19.2 2024 01 11 00 25.56 +04 45.8 6.331 6.199 77.9 8.9 19.3 2024 01 31 00 33.95 +05 43.0 6.634 6.197 59.8 7.9 19.4 2024 02 20 00 44.88 +06 56.2 6.888 6.196 42.6 6.2 19.5 2024 05 30 01 53.04 +14 19.4 6.960 6.187 37.5 5.7 19.5 2024 06 19 02 04.96 +15 36.4 6.736 6.185 53.5 7.6 19.5 2024 07 09 02 14.74 +16 42.4 6.458 6.183 69.9 8.9 19.4 2024 07 29 02 21.62 +17 34.9 6.148 6.182 87.1 9.4 19.3 2024 08 18 02 24.87 +18 10.8 5.834 6.180 105.4 9.1 19.2 2024 09 07 02 24.00 +18 27.5 5.548 6.178 124.7 7.7 19.0 2024 09 27 02 19.05 +18 23.2 5.326 6.176 145.2 5.3 19.0 2024 10 17 02 11.01 +17 59.0 5.202 6.175 166.4 2.2 18.9 2024 11 06 02 01.82 +17 21.3 5.196 6.173 169.5 1.7 18.9 2024 11 26 01 53.86 +16 41.6 5.311 6.171 148.2 4.8 18.9 2024 12 16 01 49.08 +16 12.4 5.530 6.170 126.8 7.3 19.0 2025 01 05 01 48.51 +16 02.4 5.819 6.168 106.3 8.8 19.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2022 CBAT 2022 November 20 (CBET 5191) Daniel W. E. Green