Home=Current Comets: C/2025 K1
| The German Group
| Tutorials
| Archive
| Projects, publications
| Images
| Contact
On May 24, 2025, the ATLAS team discovered an asteroidal object of magnitude 18.5 in the constellation Pegasus. Follow-up observations identified the object as cometary. Comet C/2025 K1 (ATLAS) showed a strongly condensed 15" coma and a faint, 11" tail in p.a. 255°. The comet will pass perihelion very close to the Sun (solar distance: 0.33 AU) on Oct. 8, 2025 and could then reach 9.5 mag. It will approach the Earth to within 0.58 AU on Aug. 13 and should then be of magnitude 12. However, its absolute brightness is well below the Bortle limit, so there is a high probability that the comet will disintegrate on its way towards perihelion (CBET 5557). If this should not happen the comet would be brighter than 16 mag between July 2025 and mid-January 2026, experiencing a second perigee of 0.40 AU on Nov. 25. During this period, it will move through the constellations Pegasus, Vulpecula, Hercules (1st perigee), Serpens, Libra, Virgo, Corvus (perihelion), Leo, Ursa Major (2nd perigee), Camelopardalis, Cassiopeia and Andromeda. From Central European locations it can be followed in the evening sky until the end of August (then of magnitude 12.0). If it survives the perihelion passage intact it will reappear in the morning sky around Oct. 20 (about 10.5 mag), quickly gaining altitude and finally moving towards the midnight sky.
Despite its faintness (end of July: 12.5 mag), the monitoring of the comet's development started early. Based on 183 observations from 44 observers (until mid-September 2025) the comet shows an average increase in activity that can be well represented by the parameters
m0 = 12.3 mag / n = 3.0.This means that the comet has an absolute brightness that is significantly below the Bortle limit! However, if the comet does not disintegrate and continues to develop in the current way, it would peak at 9.5 mag on Oct. 10, 2025, but would then be situated too close to the Sun for observations. In the days of perigee (end of November) it would be of magnitude 11.
Total Brightness and Coma Diameter
The apparent coma diameter increased from 0.4' to 2.0' between the beginning of June and the end of August 2025, but appears to have shrunk since then. This results in an absolute coma diameter of about 45,000 km. The degree of condensation decreased from DC 5-6 to DC 4 between mid-July and early September. CCD-observers report a tail of up to 7' (300,000 km) length, which changed its orientation from WSW to East.Andreas Kammerer
