C/2025 K1 (ATLAS)
Parabolic comet
From Wikipedia, the free encyclopedia
C/2025 K1 (ATLAS) is a non-periodic comet first seen in May 2025. It is one of many comets discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS). The comet is dynamically new, having come directly from the Oort cloud.[4] With perihelion only 0.33 AU (49 million km; 31 million mi) from the Sun, the comet was not expected to survive perihelion passage,[9] but it did and was recovered on 18 October 2025. The comet has broken into multiple fragments and fragments A+B+D should be ejected from the Solar System.[10][a] Fragment-C may remain bound to the Solar System.[6]
_2025-10-29.jpg)
Comet C/2025 K1 (ATLAS) photographed on 29 October 2025 | |
| Discovery[1] | |
|---|---|
| Discovery site | ATLAS–CHL (W68) |
| Discovery date | 24 May 2025 |
| Designations | |
| CK25K010,[2] A11nyuL | |
| Orbital characteristics[3] | |
| Epoch | 22 September 2025 (JD 2460940.5) |
| Observation arc |
|
| Earliest precovery date | 8 April 2025 |
| Number of observations | 2,395 |
| Perihelion | 0.334 AU |
| Eccentricity | |
| Orbital period | ejection (outbound A+B+D)[a] ≈449000 years (outbound-C)[6] |
| Inclination |
|
| 97.557° | |
| Argument of periapsis | 271.02° |
| Mean anomaly | –0.000° |
| Last perihelion | 8 October 2025 |
| Earth MOID | 0.161 AU |
| Jupiter MOID | 2.31 AU |
| Physical characteristics[8] | |
Mean radius | 1–2 km (0.62–1.24 mi)[b] |
| Comet total magnitude (M1) | 14.2±0.8 |
Observational history
The comet was first discovered on 24 May 2025 as an apparently asteroid-like object (temporarily designated as A11nyuL) from the ATLAS facility at Rio Hurtado, Chile.[1] At the time, it was a 19th-magnitude object with a slightly diffuse coma within the constellation Pegasus.[c] Observations from the Siding Spring Observatory noted a tail about 7.5 arcseconds long and a coma about 1.5 arcseconds across, brightening up to apparent magnitude 12.1 by 13 August 2025.[11]
_(iotw2604a).jpg)
Between 24 and 29 September, the comet was spotted in the same area of the sky from the Earth's perspective alongside C/2025 R2 (SWAN) as it gradually moved within the constellation Virgo.[13][14] In early November 2025 the comet experienced two apparent outbursts, with the comet brightening by 0.9 magnitude during the largest of which, on 4 November. On the same date, images by ZTF revealed a parabola of a material up to 10 arcseconds from the nucleus that the next day was not present while the tail had become brighter, which is consistent with the material moving tailwards.[15] This outburst later resulted with the comet experiencing a fragmentation event with two visible components. The fragmentation was first reported on the social media groups comets-ml.groups.io and Facebook by F. Kugel, Dauban Observatory MPC station A77 on October 10, 2025. (Image linked externally) and reported by ATel from the Teide Observatory on 10 November 2025.[16] By 13 November 2025, three fragments were visible.[17][18] By 25 November 2025 a fourth fragment had appeared and fragment-A had brightened significantly, which indicated other fragment(s) could become visible.[19]
On 24 November 2025 the comet passed 0.401 AU (60.0 million km; 37.3 million mi) from Earth,[20] and about 12 degrees from Dubhe in the Big Dipper. Additional observations from the Gemini North telescope in December 2025,[21] and the James Webb Space Telescope (JWST) in January 2026,[22] had detected the second fragmentation event that occurred on the comet's Fragment C.[21][22]
Images captured by Gemini North on 11 November and 6 December 2025 showed three suspected fragments of the comet's nucleus, each fluctuating in brightness, density, and position from night to night.[12]
Physical characteristics
Spectroscopic observations of the comet conducted from the Asiago Astrophysical Observatory between 3 and 15 August 2025 had revealed that its coma is significantly depleted in carbon-chain molecules, especially diatomic carbon (C2).[25] Additional data obtained from the Lowell Observatory on 19 August 2025 indicated it also has very low CN-to-OH and dust-to-gas ratios compared to other comets.[26] So far, only two other comets were known to have such carbon-poor composition, these were C/1988 Y1 (Yanaka) and 96P/Machholz.[26] On 13 November 2025, as the comet was fragmenting, the optical spectrum was dominated by NH2 while it was depleted in carbon species.[27]
