210P/Christensen

210P/Christensen is a Jupiter family periodic comet with an orbital period of 5.7 years. It was discovered by Eric J. Christensen on 26 May 2003 in images taken by the Catalina Sky Survey and recovered in images obtained by STEREO, the first time a single-apparition comet was recovered by a spacecraft.

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") 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 Marsden. This was the first recovery by a spacecraft of a single-apparition comet (a comet that had only been observed to pass the Sun once) by a spacecraft. The comet was observed from the ground on 31 November 2008, with an estimated magnitude of 11.

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.