121P/Shoemaker–Holt, also known as Shoemaker-Holt 2, is a periodiccomet in the Solar System with an orbital period of about 8 years. The comet was discovered by Carolyn S. Shoemaker, Eugene M. Shoemaker, and Henry E. Holt on 9 March 1989. The comet then had an apparent magnitude of 13, was diffuse and had a tail about 2 arcminutes long.[3] It was recovered by James V. Scotti on 29 August 1995 in images obtained as part of the Spacewatch survey.[4]
The nucleus of the comet is estimated to have a radius of 3.87 km based on infrared imaging by the Spitzer Space Telescope, when the comet displayed dust emission.[5] Observations of the comet from the Isaac Newton Telescope indicate an effective radius of 3.61 kilometers. The rotational period was calculated to be 10 hours, but with high uncertainty.[6]