Electronic Telegram No. 5058 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/2021 U1 (WIERZCHOS) Kacper W. Wierzchos, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet with a 6" asymmetric coma fanning towards p.a. 220-240 degrees on four 30-s CCD exposures obtained on Oct. 18 UT with the Mt. Lemmon 1.5-m reflector (discovery astrometry tabulated below). 2021 UT R.A. (2000) Decl. Mag. Observer Oct. 18.35166 2 49 53.08 +40 10 39.1 19.1 Wierzchos 18.35748 2 49 52.93 +40 10 35.2 19.7 " 18.36332 2 49 52.78 +40 10 30.8 19.4 " 18.36907 2 49 52.66 +40 10 26.9 19.3 " 18.38195 2 49 52.37 +40 10 17.7 19.5 " 18.38686 2 49 52.25 +40 10 14.4 19.6 " 18.39167 2 49 52.15 +40 10 10.8 19.5 " 18.41932 2 49 51.55 +40 09 51.0 19.7 " 18.42374 2 49 51.43 +40 09 47.8 19.6 " 18.42825 2 49 51.34 +40 09 44.4 19.6 " Observations made with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii, on Sept. 28.5 (mag 20.8-21.0) and on Oct. 1.6 UT (mag 20.6-20.8) -- reported in real time as two apparently separate asteroidal objects to the Minor Planet Center -- were identified in the MPC's "isolated tracklet file". R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports that the four 45-s w-band survey images on Sept. 28.5 show a condensed coma of size 1".7 (full-width-at-half-maximum) in 1".56 seeing with a possible asymmetry to the west but no clear tail, and that two 45-s w-band survey images on Oct. 1.6 show a condensed coma of size 2".1 (FWHM) in 1".6 seeing, again with no clear tail. Weryk subsequently identified four marginal Pan-STARRS1 observations (at mag 20.7-21.9) that do not show evidence of cometary activity. The available astrometry appears on MPEC 2021-U43 and includes pre-discovery observations reported to the MPC after the comet was posted on its PCCP webpage on Oct. 8.4 at mag 20.8 and on Oct. 11.3 at mag 19.8-20.2 with the Catalina Sky Survey's 0.68-m Schmidt telescope. The following preliminary elliptical orbital elements by S. Nakano (CBAT) are from 34 observations spanning 2021 Sept. 20-Oct. 19 (mean residual 0".3; the mean error in P is +/- 5.65 days). These elements suggest that the comet passed 2.36 AU from Saturn in 2016 Apr. and 1.60 AU from Jupiter in 2019 Dec. Nakano was unable to identify earlier observations in archival data but notes that such searches are preliminary. T = 2021 Sept.30.83074 TT Peri. = 144.99283 e = 0.7131699 Node = 246.79376 2000.0 q = 2.4452454 AU Incl. = 30.56056 a = 8.5250651 AU n = 0.03959657 P = 24.89 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.5 and 2.5n = 10 for the magnitudes. The available observations center on the time of perihelion passage, and it appears that there may have been an outburst in brightness at the time of discovery. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 02 50.52 +43 14.0 1.758 2.446 122.3 20.3 19.6 2021 10 03 02 52.36 +42 28.7 1.671 2.445 130.9 18.0 19.5 2021 10 13 02 51.37 +41 08.7 1.598 2.448 139.9 15.2 19.4 2021 10 23 02 48.18 +39 11.7 1.546 2.454 149.2 12.0 19.3 2021 11 02 02 43.72 +36 39.8 1.516 2.463 157.7 8.8 19.3 2021 11 12 02 39.14 +33 40.0 1.514 2.476 162.7 6.8 19.3 2021 11 22 02 35.55 +30 25.5 1.540 2.493 160.4 7.7 19.4 2021 12 02 02 33.71 +27 11.3 1.595 2.512 152.6 10.4 19.5 2021 12 12 02 34.08 +24 10.7 1.678 2.535 143.0 13.5 19.7 2021 12 22 02 36.77 +21 33.2 1.784 2.560 133.2 16.3 19.8 2022 01 01 02 41.65 +19 22.6 1.911 2.589 123.7 18.4 20.0 2022 01 11 02 48.50 +17 39.1 2.054 2.620 114.6 20.0 20.2 2022 01 21 02 57.05 +16 20.2 2.209 2.654 106.0 20.9 20.5 2022 01 31 03 07.03 +15 21.9 2.372 2.690 97.8 21.3 20.7 2022 02 10 03 18.21 +14 40.3 2.542 2.729 90.1 21.2 20.9 2022 02 20 03 30.35 +14 11.4 2.714 2.769 82.8 20.7 21.1 2022 03 02 03 43.28 +13 51.4 2.887 2.812 75.8 20.0 21.3 2022 03 12 03 56.84 +13 37.5 3.058 2.856 69.0 18.9 21.5 2022 03 22 04 10.89 +13 26.9 3.225 2.903 62.5 17.7 21.7 2022 04 01 04 25.30 +13 17.5 3.387 2.950 56.2 16.3 21.8 2022 04 11 04 39.97 +13 07.4 3.542 2.999 50.1 14.8 22.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 October 20 (CBET 5058) Daniel W. E. Green