12238 Actor/ˈæktɔːr/ is aJupiter trojan from theGreek camp, approximately 30 kilometers (19 miles) in diameter. It was discovered on 17 December 1987, by astronomersEric Elst andGuido Pizarro at theLa Silla Observatory in northern Chile.^[1] The dark Jovianasteroid has arotation period of 7.3 hours.^[6] It was named afterActor, father of the heroesEurytus and Cteatus from Greek mythology.^[1]

As allJupiter trojans,Actor is in a 1:1orbital resonance withJupiter. It is located in the leadingGreek camp at the Gas Giant'sL₄Lagrangian point, 60° ahead on its orbit(seeTrojans in astronomy).^[3] It is also a non-family asteroid of theJovian background population.^[4] It orbits the Sun at a distance of 4.5–5.8 AU once every 11 years and 9 months (4,300 days;semi-major axis of 5.17 AU). Its orbit has aneccentricity of 0.12 and aninclination of 21° with respect to theecliptic.^[2]

The body'sobservation arc begins with its first observation as1986 WW₈ at theKiso Observatory in November 1986, or 13 months prior to its official discovery observation at La Silla.^[1]

Thisminor planet was named fromGreek mythology afterActor (son of Phorbas and Hyrmine), the alleged father of the twin brothersEurytus and Cteatus, who beatNestor, king ofPylos, in achariot race.^[1] The official naming citation was published by theMinor Planet Center on 6 January 2003 (M.P.C. 47300).^[8]

Actor is an assumedC-type asteroid, while the majority of largerJupiter trojans areD-types.^[6]

In 2007, a rotationallightcurve ofActor was obtained fromphotometric observations at theSierra Nevada Observatory, using its 1.5-meter telescope. Lightcurve analysis gave arotation period of 7.284 hours with a brightness variation of 0.30magnitude (U=2).^[7] The same group also published a period determination of7.28±0.02 hours with an amplitude of 0.33 magnitude in 2010.^[6][9]

In July and August 2015, observations by theKepler space telescope during itsK2 mission gave another two lightcurves with a concurring period of 7.28 and 7.281 hours, respectively. Both measurements had a brightness variation of 0.29 magnitude (U=2/2).^[10][11]

According to the survey carried out by theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer,Actor measures 30.25 kilometers in diameter and its surface has analbedo of 0.092,^[5] while theCollaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 36.78 kilometers based on anabsolute magnitude of 10.9.^[6]

• Asteroid Lightcurve Database (LCDB), query form (infoArchived 16 December 2017 at theWayback Machine)
• Dictionary of Minor Planet Names, Google books
• Discovery Circumstances: Numbered Minor Planets (10001)-(15000) – Minor Planet Center
• Asteroid 12238 ActorArchived 5 July 2018 at theWayback Machine at the Small Bodies Data Ferret
• 12238 Actor atAstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 12238 Actor at theJPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

• Minor planet object articles (numbered)
• Jupiter trojans (Greek camp)
• Discoveries by Eric Walter Elst
• Discoveries by Guido Pizarro (astronomer)
• Named minor planets
• Astronomical objects discovered in 1987

• Articles with short description
• Short description matches Wikidata
• Use dmy dates from July 2018
• Webarchive template wayback links