C/2025 K1 (ATLAS)

Type: Hyperbolic Perihelion date: 8 October 2025 Perihelion distance (q): 0.3 Aphelion distance (Q) : n/a Period (years): n/a Eccentricity (e): 1.00 Inclination (i): 147.9 JPL orbit diagram COBS lightcurve Atlas The ATLAS (Asteroid Terrestrial-impact Last Alert System) team discovered a 19th magnitude object in images taken with the 0.5 m Schmidt at Rio Hurtado, Chile on 24 May 2025. There were pre-discovery images from the Palomar ZTF Schmidt on May 19 and 22. The intriniscally faint comet was thought unlikely to survive past perihelion at 0.3 au in October 2025, but was recovered in late October at around 10th magnitude. The ion tail showed a reddish colour, rather than the usual blue, which may reflect carbon depletion, with H2O+ rather than CO+ the predominant ion. Professional observations also suggest that the nucleus was undergoing some spallation between 30 October and 5 November, resulting in fluctuation over the near nucleus magnitude. HST observations showed one major and one minor fragment, which were then imaged by amateurs from the ground. Amateurs continued to observe three bodies in mid November, though these varied in brightness, with sometimes one and sometimes another being the brightest. The MPC designated the fragment which was first observed on 5 November as B, stating that it was first observed with the Discovery Telescope. The third fragement was first reported to the MPC by Nick James in images taken on 15 November from Tenerife and was designated as C. Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 28-Jun-25 16.7 0.4 19-Jul-25 14.2 0.9 31-Jul-25 13.4 0.7 19-Aug-25 12.9 1.1 24-Aug-25 13.0 1.0 30-Nov-25 12.0 0.7 10-Dec-25 15.7 0.2 Fragment C 10-Dec-25 13.1 1.0