18493 Demoleon (/dɪˈmoʊliən/provisional designation 1996 HV₉) is a Jupiter trojan from the Trojan camp, approximately 33 kilometers (21 miles) in diameter. It was discovered by Belgian astronomer Eric Elst at ESO's La Silla Observatory in northern Chile on 17 April 1996.^[1] The dark Jovian asteroid has a rotation period of 14.4 hours.^[7] It was named after the Trojan warrior Demoleon from Greek mythology.^[1]

Demoleon is a dark Jovian asteroid in a 1:1 orbital resonance with Jupiter. It is located in the trailering Trojan camp at the Gas Giant's L₅ Lagrangian point, 60° behind on its orbit (see Trojans in astronomy). It is also a non-family asteroid of the Jovian background population.^[5] It orbits the Sun at a distance of 4.8–5.8 AU once every 12 years and 2 months (4,454 days; semi-major axis of 5.3 AU). Its orbit has an eccentricity of 0.09 and an inclination of 17° with respect to the ecliptic.^[3] The body's observation arc begins with a precovery published by the Digitized Sky Survey and taken at Palomar Observatory in November 1989, more than 6 years prior to its official discovery observation at La Silla.^[1]

This minor planet was named from Greek mythology after the Trojan warrior Demoleon, son of Antenor, who was a counselor to King Priam. Demoleon, a valiant champion of war was killed by Achilles, whose spear struck Demoleon on the temple through his bronze-cheeked helmet, crushing the bone so that the brain inside was shed in all directions.^[1] The official naming citation was published by the Minor Planet Center on 27 May 2010 (M.P.C. 70409).^[10]

Demoleon is an assumed C-type asteroid, while most larger Jupiter trojans are D-types.^[7] It has a low V–I color index of 0.775 (see table below).^[9]