121P/Shoemaker–Holt

For other comets discovered by Carolyn and Eugene Shoemaker, see Comet Shoemaker.

121P/Shoemaker–Holt, also known as Shoemaker-Holt 2, is a periodic comet 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.^[6] It was recovered by James V. Scotti on 29 August 1995 in images obtained as part of the Spacewatch survey.^[7]

121P/Shoemaker-Holt

Discovery
Discovered by	Carolyn S. Shoemaker Eugene Merle Shoemaker Henry E. Holt
Discovery date	March 9, 1989
Designations
Alternative designations	1989j; 1988 XI; 1995 Q3
Orbital characteristics
Epoch	March 6, 2006
Aphelion	5.376 AU
Perihelion	2.65 AU
Semi-major axis	4.013 AU
Eccentricity	0.3396
Orbital period	8.039 a
Inclination	17.7218°
Last perihelion	September 8, 2013[1] September 1, 2004
Next perihelion	2023-Jun-28[2]
Physical characteristics[3][4][5]
Mean radius	3.61 km (2.24 mi)
Synodic rotation period	~10 hours
Spectral type	(V–R) = 0.53±0.03

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.^[4] 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.^[3]