C/2025 K1 (ATLAS)

For other comets discovered by the Asteroid Terrestrial-impact Last Alert System, see Comet ATLAS.

C/2025 K1 (ATLAS) is an Oort cloud 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, but it did and was recovered on 18 October 2025. The comet is around apparent magnitude 9.5,^[5] and visible in large binoculars. As of the start of November 2025, the comet can be seen just before sunrise.

C/2025 K1 (ATLAS)

Comet C/2025 K1 (ATLAS) photographed on 7 August 2025
Discovery[1]
Discovery site	ATLAS–CHL (W68)
Discovery date	24 May 2025
Designations
Alternative designations	CK25K010,[2] A11nyuL
Orbital characteristics[3]
Epoch	24 July 2025 (JD 2460880.5)
Observation arc	202 days
Earliest precovery date	8 April 2025
Number of observations	2,236
Perihelion	0.334 AU
Eccentricity	0.999999 (inbound)[4] 1.0002 (outbound)
Inclination	147.86°
Longitude of ascending node	97.557°
Argument of periapsis	271.03°
Mean anomaly	–0.002°
Last perihelion	8 October 2025
Earth MOID	0.161 AU
Jupiter MOID	2.313 AU
Comet total magnitude (M1)	14.1

On 24 November 2025 the comet will pass 0.401 AU (60.0 million km; 37.3 million mi) from Earth,^[6] and will be about 12 degrees from Dubhe in the Big Dipper.

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).^[7] 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.^[8] So far, only two other comets were known to have such carbon-poor composition, these were C/1988 Y1 (Yanaka) and 96P/Machholz.^[8]