C/2025 D1 (Gröller)

Comet Gröller, also known as C/2025 D1 (Gröller), is a very distant non-periodic comet discovered by Hannes Gröller of the Catalina Sky Survey on 20 February 2025. It is the comet with the most distant perihelion ever known,^[5] which will approach the Sun no closer than 14.12 AU (2.112 billion km) by May 2028,^[3] surpassing the record previously held by C/2003 A2 (Gleason) by 2.7 AU.^[5][6]

C/2025 D1 (Gröller)

Discovery[1][2]
Discovered by	Hannes Gröller
Discovery site	Kitt Peak, Arizona (Bok Telescope)
Discovery date	20 February 2025
Orbital characteristics[3]
Epoch	24 June 2024 (JD 2460485.5)
Observation arc	6.90 years (2,522 days)
Earliest precovery date	6 June 2018
Number of observations	66
Perihelion	14.123 AU
Eccentricity	1.00302
Orbital period	~6 million years (inbound)
Inclination	84.491°
Longitude of ascending node	312.89°
Argument of periapsis	185.85°
Mean anomaly	–0.004°
Next perihelion	18 May 2028
Earth MOID	13.143 AU
Jupiter MOID	8.826 AU
Physical characteristics[4]
Mean radius	≥ 0.4 km (0.25 mi)
Comet total magnitude (M1)	6.6

It was Hannes Gröller's fourth comet discovery since 2019.^[a]

Observational history

The comet was discovered by Hannes Gröller using the 2.25 m (7.4 ft) Bok Telescope of the Kitt Peak Observatory in Arizona.^[2] Images obtained through stacking of 30-second exposures show a magnitude 20.6 object with a condensed coma measuring 3 arcseconds across.^[1][7] Amateur astronomer Sam Deen found several precovery observations of C/2025 D1 from 2018, when the comet was more than 21 AU (3.1 billion km) from the Sun (beyond the orbit of Uranus).^[5] This makes C/2025 D1 one of the few known "ultradistant comets" that have been observed beyond 20 AU (3.0 billion km) from the Sun.^[5] The ultradistant comets, which include the giant Oort cloud comet C/2014 UN₂₇₁ (Bernardinelli–Bernstein), are believed to contain supervolatile compounds such as carbon monoxide and carbon dioxide, which are known to easily vaporize at low temperatures far from the Sun.^[5]

Orbit

Astrometric measurements and orbital calculations reveal that C/2025 D1 is a dynamically new comet from the Oort cloud, with its previous perihelion distance approximately 6 million years ago were estimated to be greater than or equal to 60 AU (9.0 billion km).^[4] It will reach its next perihelion on 18 May 2028,^[3] and is expected to be ejected from the Solar System on its outbound flight.^[4]

See also

Other ultradistant comets:

• Comet Hale–Bopp
• C/2010 U3 (Boattini)
• C/2017 K2 (PanSTARRS)
• C/2014 UN₂₇₁ (Bernardinelli–Bernstein)
• C/2019 E3 (ATLAS)

Notes

1. Hannes Gröller previously discovered the following three comets between 2019 and 2021. These were P/2019 B2, P/2019 V2, and P/2021 R6