Electronic Telegram No. 5580 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/2025 N2 (ATLAS) An apparently asteroidal object discovered on CCD images taken on July 2.1 UT with a 0.5-m f/2 Schmidt reflector at Sutherland, South Africa, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program has been found to show cometary appearance by observers elsewhere. The discovery observations are tabulated below: 2025 UT R.A. (2000) Decl. Mag. July 2.06465 0 03 25.69 -81 14 27.9 19.6 2.06788 0 03 25.97 -81 14 29.1 19.4 2.07334 0 03 26.18 -81 14 31.4 19.1 2.09616 0 03 27.48 -81 14 40.6 19.3 2.10664 0 03 28.38 -81 14 44.4 19.4 S. Deen (Simi Valley, CA, USA) writes that he obtained a single 10-min CMOS exposure of this object on July 2.20 UT with a 0.43-m reflector at Rio Hurtado, Chile, with a star-like coma and a possible very faint 2"-long tail in p.a. 270 degrees. He then searched through public-archive images and found two images of the comet obtained in 2023 with the 4-m reflector (+ DECam) at Cerro Tololo (with astrometry given below). On 2023 July 13 in 1".4 seeing, the comet appears slightly diffuse with a 1".6 coma (full-width-at-half- maximum) and a possible short, broad tail centered at p.a. 315 degrees. On 2023 Oct. 25 in 1".2 seeing, the comet appears somewhat diffuse with a coma of size 1".9 (FWHM) and no discernible tail. The magnitudes are very approximate, due to a lack of available comparison stars for photometry. 2023 UT R.A. (2000) Decl. Mag. July 13.08594 18 36 40.31 -49 48 44.8 22.0 Oct. 25.03214 18 16 17.79 -50 58 13.7 21.2 Deen also identified images of this comet in CCD images taken on 2025 May 7 UT with the ATLAS 0.5-m f/2 Schmidt reflector at Sutherland, as well as numerous images on CCD exposures taken with an ATLAS 0.5-m f/2 Schmidt reflector at Rio Hurtado, Chile, on June 6, 18, and 24 -- as tabulated below. The comet was very faint in the ATLAS images, so it's not possible to comment on specific details other than that it appears generally cometary in the clearer of the images. 2025 UT R.A. (2000) Decl. May 7.08847 22 51 16.78 -75 02 09.3 7.09172 22 51 16.79 -75 02 09.5 7.11136 22 51 18.54 -75 02 16.8 7.12539 22 51 19.57 -75 02 22.1 June 6.39857 23 33 36.24 -78 20 01.4 6.39902 23 33 36.30 -78 20 04.0 6.41563 23 33 37.74 -78 20 09.3 6.41608 23 33 37.93 -78 20 09.1 6.42638 23 33 38.84 -78 20 13.6 6.42683 23 33 38.53 -78 20 15.3 18.31859 23 48 31.93 -79 41 24.9 18.32139 23 48 31.59 -79 41 26.1 18.32464 23 48 32.53 -79 41 28.0 24.12025 23 55 11.93 -80 20 57.2 24.12674 23 55 12.21 -80 20 59.9 24.13414 23 55 13.30 -80 21 03.8 Ten stacked 60-s CCD exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) using a 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, on 2025 July 2.4 UT show only a stellar appearance; the magnitude was 19.1 as measured within a circular aperture of radius 2".2. Twelve stacked 60-s exposures taken by Sato with the same instrumentation on July 8.4 show a strongly condensed coma 7" in diameter with a hint of tail 40" long toward p.a. 270 degrees; the magnitude was 18.8 as measured within a circular aperture of radius 3".6. Additional astrometry appears on MPEC 2025-N76. The following orbital elements by S. Nakano (Central Bureau) are from 35 observations spanning 2023 July 13-2025 July 8 (mean residual 0".6), with corresponding "original" and "future" values of 1/a being +0.000071 and +0.000054 (+/- 0.000014) AU**-1, respectively. There are no close approaches to major planets. Epoch = 2024 Nov. 26.0 TT T = 2024 Dec. 12.92836 TT Peri. = 230.12304 e = 1.0029119 Node = 94.46084 2000.0 q = 8.9846850 AU Incl. = 81.66283 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 6.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 06 14 23 43.29 -79 11.9 8.614 9.046 112.1 6.0 18.8 2025 06 24 23 55.07 -80 20.1 8.596 9.053 113.7 5.9 18.8 2025 07 04 00 05.24 -81 27.3 8.593 9.060 114.4 5.9 18.8 2025 07 14 00 13.10 -82 32.1 8.605 9.068 114.1 5.9 18.8 2025 07 24 00 17.58 -83 33.2 8.631 9.076 112.9 5.9 18.8 2025 08 03 00 17.08 -84 29.1 8.671 9.084 111.0 6.0 18.9 2025 08 13 00 09.61 -85 17.9 8.723 9.092 108.3 6.1 18.9 2025 08 23 23 52.97 -85 57.2 8.784 9.101 105.2 6.2 18.9 2025 09 02 23 26.35 -86 24.0 8.855 9.111 101.6 6.2 18.9 2025 09 12 22 52.91 -86 35.9 8.931 9.120 97.7 6.3 18.9 2025 09 22 22 20.15 -86 32.4 9.012 9.130 93.6 6.3 19.0 2025 10 02 21 55.58 -86 15.4 9.095 9.141 89.5 6.3 19.0 2025 10 12 21 42.01 -85 48.7 9.178 9.152 85.3 6.2 19.0 2025 10 22 21 38.37 -85 15.1 9.260 9.163 81.3 6.2 19.0 2025 11 01 21 42.34 -84 36.8 9.337 9.174 77.5 6.1 19.1 2025 11 11 21 51.67 -83 55.0 9.409 9.186 74.0 5.9 19.1 2025 11 21 22 04.65 -83 10.4 9.474 9.198 70.9 5.8 19.1 2025 12 01 22 20.06 -82 23.5 9.531 9.210 68.2 5.7 19.1 2025 12 11 22 37.02 -81 34.6 9.579 9.223 66.0 5.6 19.1 2025 12 21 22 54.95 -80 44.1 9.617 9.236 64.5 5.5 19.1 2025 12 31 23 13.44 -79 52.5 9.646 9.249 63.5 5.5 19.2 2026 01 10 23 32.19 -79 00.0 9.665 9.263 63.2 5.4 19.2 2026 01 20 23 51.04 -78 07.2 9.674 9.277 63.5 5.4 19.2 2026 01 30 00 09.86 -77 14.5 9.675 9.291 64.4 5.5 19.2 2026 02 09 00 28.55 -76 22.6 9.667 9.306 65.8 5.5 19.2 2026 02 19 00 47.08 -75 31.8 9.653 9.321 67.6 5.6 19.2 2026 03 01 01 05.40 -74 42.8 9.632 9.336 69.8 5.7 19.2 2026 03 11 01 23.48 -73 56.2 9.607 9.352 72.2 5.8 19.2 2026 03 21 01 41.31 -73 12.3 9.578 9.368 74.9 5.9 19.2 2026 03 31 01 58.87 -72 31.8 9.548 9.384 77.6 6.0 19.2 2026 04 10 02 16.11 -71 55.1 9.517 9.401 80.3 6.0 19.2 2026 04 20 02 33.04 -71 22.5 9.487 9.418 83.0 6.1 19.2 2026 04 30 02 49.59 -70 54.6 9.459 9.435 85.6 6.1 19.2 2026 05 10 03 05.73 -70 31.7 9.434 9.452 88.0 6.1 19.2 2026 05 20 03 21.42 -70 14.0 9.412 9.470 90.2 6.1 19.2 2026 05 30 03 36.58 -70 01.7 9.396 9.488 92.1 6.1 19.2 2026 06 09 03 51.15 -69 55.1 9.385 9.506 93.8 6.1 19.2 2026 06 19 04 05.05 -69 54.2 9.380 9.525 95.1 6.1 19.2 2026 06 29 04 18.18 -69 58.9 9.381 9.544 96.2 6.1 19.2 2026 07 09 04 30.43 -70 09.3 9.389 9.563 96.8 6.1 19.2 2026 07 19 04 41.67 -70 25.0 9.402 9.583 97.2 6.0 19.2 2026 07 29 04 51.75 -70 45.8 9.421 9.602 97.3 6.0 19.2 2026 08 08 05 00.52 -71 11.0 9.446 9.623 97.0 6.0 19.2 2026 08 18 05 07.78 -71 40.2 9.475 9.643 96.5 6.0 19.3 2026 08 28 05 13.30 -72 12.4 9.509 9.664 95.8 6.0 19.3 2026 09 07 05 16.87 -72 46.5 9.547 9.684 94.8 6.0 19.3 2026 09 17 05 18.24 -73 21.3 9.588 9.706 93.7 5.9 19.3 2026 09 27 05 17.19 -73 54.9 9.632 9.727 92.5 5.9 19.3 2026 10 07 05 13.59 -74 25.7 9.678 9.749 91.1 5.9 19.3 2026 10 17 05 07.36 -74 51.4 9.725 9.771 89.7 5.9 19.4 2026 10 27 04 58.70 -75 09.9 9.772 9.793 88.3 5.8 19.4 2026 11 06 04 48.00 -75 18.9 9.820 9.815 86.9 5.8 19.4 2026 11 16 04 35.95 -75 16.7 9.867 9.838 85.4 5.8 19.4 2026 11 26 04 23.45 -75 02.2 9.914 9.861 84.1 5.7 19.4 2026 12 06 04 11.41 -74 35.0 9.959 9.884 82.8 5.7 19.5 2026 12 16 04 00.66 -73 55.6 10.003 9.908 81.6 5.6 19.5 2026 12 26 03 51.78 -73 05.2 10.046 9.932 80.5 5.6 19.5 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 July 9 (CBET 5580) Daniel W. E. Green