210P/Christensen
First single-apparition comet recovered by a spacecraft.
210P/Christensen is a Jupiter-family comet that orbits the Sun once every 5.7 years. It holds the distinction of being the first comet observed in only one previous apparition to be rediscovered by a spacecraft, in this case NASA's STEREO mission.
The comet was first spotted by Eric J. Christensen on 26 May 2003, using the 0.7-meter Schmidt telescope of the Catalina Sky Survey. At the time, it had an estimated brightness of magnitude 14.6, a coma spanning 10 to 35 arcseconds, and a faint tail. Subsequent observations showed it had a short orbital period.
In mid-December 2008, Australian amateur astronomer Alan Watson noticed a cometary object in data from the STEREO/SECCHI Heliospheric Imager (HI-1B). German comet observer Rainer Kracht calculated a rough set of orbital elements from a few positions in the data. Maik Meyer then recognized that these elements matched those of P/2003 K2, and Brian G. Marsden confirmed the link. This marked the first recovery of a single-apparition comet by a spacecraft. Ground-based observations followed on 14 December 2008, when the comet was low in bright twilight, and by 31 December 2008 its magnitude had brightened to an estimated 10.5.
During its 2025 return, the comet passed 0.43 AU (64 million km) from Earth on 8 November 2025, though it was only 20 degrees from the Sun. It reached perihelion on 22 November 2025. In November 2025, it was visible in the SWAN instrument at about magnitude 11. On 26 November 2025, it appeared low in the morning twilight with a faint tail roughly a quarter of a degree long and an estimated magnitude of 9.5.
The comet has been locked in a 2:1 orbital resonance with Jupiter for the past 10,000 years and may have an asteroidal origin. Its nucleus is estimated to be about 1.74 km (1.08 mi) in diameter. It makes close approaches to Venus; on 17 September 1929, it passed just 0.032 AU (4.8 million km) from the planet.
Quick Facts
- Discovery Ref
- IAUC_8136
- Discoverer
- Eric J. Christensen
- Discovery Site
- Catalina Sky Survey
- Discovery Date
- 26 May 2003
- Mpc Name
- P/2003 K2, P/2008 X4
- Orbit Ref
- jpldata · MPC
- Epoch
- 21 November 2025 (JD 2461000.5)
- Obs
- 1,329
- Perihelion
- 0.524 AU
- Aphelion
- 5.797 AU
- Semimajor
- 3.161 AU
- Eccentricity
- 0.83408
Facts from the source article.
Lore & Background
Eric J. Christensen discovered the comet on 26 May 2003 in images taken with the 0.7-m Schmidt telescope of the Catalina Sky Survey. The comet had an estimated magnitude of 14.6 and a coma with an estimated diameter between 10 and 35 arcseconds and a faint tail. Further observations revealed the comet had a short orbital period. In mid December 2008, Australian comet-hunter Alan Watson spotted in the STEREO/SECCHI Heliospheric Imager HI-1B data a cometary object. Veteran German comet hunter Rainer Kracht recorded a few positions of the comet in the data and produced a set of very approximate orbital elements for it. Maik Meyer noticed the similarity of these orbital elements to those of P/2003 K2 and the link was confirmed by Brian G. Marsden. This was the first recovery of a single-apparition comet by a spacecraft. The comet was observed from the ground on 14 December 2008, located low and in bright twilight, and on 31 December 2008 it had an estimated magnitude of 10.5. During the 2025 apparition, the comet passed 0.43 AU from Earth on 8 November 2025 but was only 20 degrees from the Sun. It came to perihelion on 22 November 2025. It was visible in SWAN in November 2025 around magnitude 11. On 26 November it was visible low in the morning twilight, with a faint tail about a quarter of a degree long and an estimated magnitude of 9.5. The comet has been locked in a 2:1 orbital resonance with Jupiter for the last 10,000 years and could be of asteroidal origin. Its nucleus is estimated to be about 1.74 km in diameter. It makes close approaches to Venus and on 17 September 1929 passed 0.032 AU from Venus.
Reader's Guide
210P/Christensen holds a unique place in cometary astronomy as the first single-apparition comet ever recovered by a spacecraft, specifically by the STEREO mission in 2008. This recovery, facilitated by amateur astronomers Alan Watson, Rainer Kracht, and Maik Meyer, and confirmed by Brian G. Marsden, demonstrated the growing role of space-based assets in tracking comets. The comet's orbital resonance with Jupiter over the last 10,000 years suggests a long-term dynamical stability, and its possible asteroidal origin hints at a complex history. Its 2025 apparition provided observational data from both the SWAN instrument and ground-based observers, with the comet reaching magnitude 9.5. The close approach to Venus in 1929 further underscores its dynamical interactions within the inner solar system. The comet's nucleus, estimated at 1.74 km, is typical for a Jupiter-family comet, and its recovery by STEREO marked a milestone in the use of spacecraft for comet follow-up.
Did You Know?
- 210P/Christensen was discovered by Eric J. Christensen on 26 May 2003 using the Catalina Sky Survey's 0.7-m Schmidt telescope.
- It was the first single-apparition comet recovered by a spacecraft, via STEREO in 2008.
- On 17 September 1929, it passed 0.032 AU from Venus.
More in Periodic Comets 1-24
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