18D/Perrine–Mrkos

18D/Perrine–Mrkos is a periodic comet in the Solar System, originally discovered by the American-Argentine astronomer Charles Dillon Perrine (Lick Observatory, California, United States) on December 9, 1896. For some time it was thought to be a fragment of Biela's Comet.^[4]

18D/Perrine–Mrkos

The comet on 11 October 1909 by the Heidelberg-Königstuhl State Observatory
Discovery
Discovered by	Charles Dillon Perrine & Antonín Mrkos
Discovery date	December 9, 1896
Designations
Alternative designations	1896 X1; 1896 VII; 1896g; 1909 P1; 1909 III; 1909b; 1955 U1; 1955 VII; 1955i; 1962 I; 1961h; 1968 VIII; 1968h
Orbital characteristics
Epoch	2002-09-03 (JD 2452520.5)
Aphelion	5.8537 AU
Perihelion	1.2872 AU
Semi-major axis	3.5705 AU
Eccentricity	0.6395
Orbital period	6.75 a
Inclination	17.864°
Last perihelion	2017 Feb. 26?[1] (unobserved)
Next perihelion	≈2025-Jan-01?[1][2] (Lost since 1969)[3]

It was considered lost after the 1909 appearance, but was rediscovered by the Czech astronomer Antonín Mrkos (Skalnate Pleso Observatory, Slovakia) on October 19, 1955, using ordinary binoculars, it was later confirmed as 18D by Leland E. Cunningham (Leuschner Observatory, University of California, Berkeley).

The comet was last observed during the 1968 perihelion passage when it passed 0.3144 AU (47,030,000 km; 29,230,000 mi) from the Earth.^[5] The comet has not been observed during the following perihelion passages:^[1]

• 1975 Aug. 2
• 1982 May 16
• 1989 Feb. 28
• 1995 Dec. 6 (apmag 19?)
• 2002 Sept.10 (apmag 20?)
• 2009 Apr. 17 (apmag 24?)
• 2017 Feb. 26 (apmag 24?)

The next predicted perihelion passage would be on 2025-Jan-01^[1][2] but the comet is currently considered lost as it has not been seen since Jan 1969.^[3]