121P/Shoemaker–Holt

{{Short description|Periodic comet with an eight-year orbit}}

{{For|other comets discovered by Carolyn and Eugene Shoemaker|Comet Shoemaker}}

{{Infobox comet

| name=121P/Shoemaker-Holt

| image= 121P 2006-08-01 Spitzer image Level-2-PBCD-MIPS-24um.png

| discoverer=Carolyn S. Shoemaker
Eugene Merle Shoemaker
Henry E. Holt

| discovery_date=March 9, 1989

| designations=1989j; 1988 XI; 1995 Q3

| epoch=March 6, 2006

| semimajor=4.013 AU

| perihelion=2.65 AU

| aphelion=5.376 AU

| eccentricity=0.3396

| period=8.039 a

| inclination= 17.7218°

| physical_ref = {{r|Snodgrass_2008|Fernández_2013|Knight_2023}}

| mean_radius = {{cvt|3.61|km|mi}}

| rotation = ~10 hours

| spectral_type = (V–R) {{=}} {{val|0.53|0.03}}

| last_p=September 8, 2013{{cite web

|date=2010-04-28

|title=121P/Shoemaker-Holt 2 (NK 1925)

|publisher=OAA Computing and Minor Planet Sections

|author=Syuichi Nakano

|author-link=Syuichi Nakano

|url=http://www.oaa.gr.jp/~oaacs/nk/nk1925.htm

|accessdate=2012-02-25}}
September 1, 2004

| next_p=2023-Jun-28{{cite web

|title=121P/Shoemaker-Holt Orbit

|url=http://www.minorplanetcenter.net/db_search/show_object?object_id=121P

|publisher=Minor Planet Center

|accessdate=2014-06-17}}

}}

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.{{cite journal |last1=Green |first1=Daniel |title=IAUC 4755: 1989j; U Gem; 1989B; N Vul 1987 |website=www.cbat.eps.harvard.edu |date=10 March 1989 |url=http://www.cbat.eps.harvard.edu/iauc/04700/04755.html}} It was recovered by James V. Scotti on 29 August 1995 in images obtained as part of the Spacewatch survey.{{cite journal |last1=Scotti |first1=J. V. |last2=Green |first2=D. W. E. |last3=Marsden |first3=B. G. |title=Comet P/1995 Q3 (Shoemaker-Holt 2) |journal=International Astronomical Union Circular |date=1 September 1995 |issue=6219 |pages=2 |url=http://www.cbat.eps.harvard.edu/iauc/06200/06219.html#Item2 |issn=0081-0304}}

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.{{r|Fernández_2013}} 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.{{r|Snodgrass_2008}}