{ "id": "epwtw5p0by", "slug": "12238-actor", "title": "12238 Actor", "updated": "2026-10-25", "topic_path": [ { "id": "places", "label": "Places and geography", "api_url": "https://www.edgepedia.org/api/v1/topics/places" }, { "id": "places.extraterrestrial", "label": "Extraterrestrial places", "api_url": "https://www.edgepedia.org/api/v1/topics/places.extraterrestrial" }, { "id": "places.extraterrestrial.small-bodies", "label": "Small bodies of the Solar System", "api_url": "https://www.edgepedia.org/api/v1/topics/places.extraterrestrial.small-bodies" }, { "id": "places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups", "label": "Jupiter Trojans and other dynamical groups", "api_url": "https://www.edgepedia.org/api/v1/topics/places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups" }, { "id": "places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans", "label": "Greek-camp Jupiter Trojans", "api_url": "https://www.edgepedia.org/api/v1/topics/places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans" }, { "id": "places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors", "label": "Lesser Achaean warriors", "api_url": "https://www.edgepedia.org/api/v1/topics/places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors" } ], "geo": [ { "id": "geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors", "label": "Non-geographic · Not dated: Lesser Achaean warriors", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.nodate", "label": "Non-geographic · Not dated", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate" }, { "id": "geo.nongeo.nodate.places", "label": "Places and geography", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places" }, { "id": "geo.nongeo.nodate.places.extraterrestrial", "label": "Extraterrestrial places", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places.extraterrestrial" }, { "id": "geo.nongeo.nodate.places.extraterrestrial.small-bodies", "label": "Small bodies of the Solar System", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places.extraterrestrial.small-bodies" }, { "id": "geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups", "label": "Jupiter Trojans and other dynamical groups", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups" }, { "id": "geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans", "label": "Greek-camp Jupiter Trojans", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans" }, { "id": "geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors", "label": "Lesser Achaean warriors", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.nodate.places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors" } ] } ], "excerpt": "12238 Actor is a Jupiter Trojan asteroid discovered by Eric Elst and Guido Pizarro in 1987 at the La Silla Observatory in Chile, named after Actor of Greek mythology.", "snippet": "12238 Actor is a Jupiter Trojan asteroid discovered by Eric Elst and Guido Pizarro in 1987 at the La Silla Observatory in Chile, named after Actor of Greek mythology.", "node": "places.extraterrestrial.small-bodies.asteroids-trojans-and-outer-groups.greek-camp-jupiter-trojans.lesser-achaean-warriors", "markdown": "# 12238 Actor\n\n**12238 Actor** is a Jupiter [Trojan](https://www.edgepedia.org/trojan-celestial-body) asteroid discovered on 17 December 1987 by Eric Elst and Guido Pizarro at the [La Silla Observatory](https://www.edgepedia.org/la-silla-observatory) in Chile.[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238) A precovery observation from November 1986 at the Kiso Observatory predates the discovery by 13 months.[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238) It is named after Actor, father of the twin heroes Eurytus and Cteatus in [Greek mythology](https://www.edgepedia.org/greek-mythology).[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238) The asteroid orbits the Sun at distances of 4.5 to 5.8 AU once every 11 years and 9 months, with an eccentricity of 0.12 and an inclination of 21° with respect to the ecliptic.[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238)\n\n|---|---|\n| Discovery | 17 December 1987, Eric Elst and Guido Pizarro, La Silla Observatory, Chile[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238) |\n| Name | Actor, father of the heroes Eurytus and Cteatus in Greek mythology[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238) |\n\n## Discovery and observations\n\nA precovery observation, a recorded sighting made before the official discovery, dates to November 1986 at the Kiso Observatory, 13 months earlier.[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238)\n\nStellar occultations by Actor have been predicted for ground-based observers. A RECON event prediction for 3 April 2025, visible from southern Africa, gave a cross-track diameter estimate of 38.7 km assuming a 5% albedo, with an expected flux drop of 68% and a maximum central chord of 2.9 seconds.[1](https://www2.boulder.swri.edu/~buie/recon/trojans/12238_Actor_20250403192059.html) A further event was predicted for 23 May 2026.[2](https://www.boulder.swri.edu/~buie/recon/trojans/12238_Actor_20260523100721.html)\n\n## Orbit and classification\n\nIt orbits the Sun at distances of 4.5 to 5.8 AU once every 11 years and 9 months (4,300 days; semi-major axis 5.17 AU), with an eccentricity of 0.12 and an inclination of 21° with respect to the ecliptic.[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238)\n\nThese orbital parameters sit within the broader Trojan population. Trojan inclinations cover a fairly uniform range from 0° to 35° in both the L4 and L5 regions, with a median inclination of 10°, and Trojan eccentricities tend to be below 0.15, values required to remain within the stable zones.[3](https://link.springer.com/article/10.1007/s11214-023-01031-4) Actor's 21° inclination places it in the more highly excited part of that distribution.\n\n## Physical properties\n\nDark, low-albedo surfaces are typical of the Trojans, which are dominated by D- and P-type bodies with featureless visible and near-infrared spectra and albedos consistent with dormant comets.[3](https://link.springer.com/article/10.1007/s11214-023-01031-4)\n\n## Naming\n\nThe minor planet is named after Actor (son of Phorbas and Hyrmine in the sources' account), father of the twin heroes Eurytus and Cteatus, who defeated Nestor, king of Pylos, in a chariot race in Greek mythology.[5](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238) Larger Trojan members are named after characters from the epic Greek poems describing the Trojan war, the *Iliad* and the *Odyssey*.[4](https://academic.oup.com/mnras/article/495/4/4085/5837576)\n\n## Context within the Trojan swarms\n\nThe [Jupiter Trojans](https://www.edgepedia.org/jupiter-trojans) are two swarms of small bodies trapped at the L4 and L5 Lagrange points of Jupiter, which has a semi-major axis of 5.2 AU.[3](https://link.springer.com/article/10.1007/s11214-023-01031-4) The largest known member is (624) Hektor at a diameter of about 250 km, while the smallest observed Trojans are roughly a kilometer across.[3](https://link.springer.com/article/10.1007/s11214-023-01031-4) Most Trojans many tens of kilometers in diameter or larger, a size class that includes Actor, are on stable orbits and are presumed survivors of the processes that created the population.[3](https://link.springer.com/article/10.1007/s11214-023-01031-4) The Trojans are thought to have been captured early in [Solar System](https://www.edgepedia.org/solar-system) history, most likely from the primordial [Kuiper belt](https://www.edgepedia.org/kuiper-belt) during a giant planet instability, rather than having formed in situ near Jupiter.[3](https://link.springer.com/article/10.1007/s11214-023-01031-4)\n\n## References\n\n1. [RECON event prediction for 12238_Actor_20250403192059, Southwest Research Institute](https://www2.boulder.swri.edu/~buie/recon/trojans/12238_Actor_20250403192059.html)\n2. [RECON event prediction for 12238_Actor_20260523100721, Southwest Research Institute](https://www.boulder.swri.edu/~buie/recon/trojans/12238_Actor_20260523100721.html)\n3. [Bottke, W. F. et al. (2023). Origin and Evolution of Jupiter's Trojan Asteroids. Space Science Reviews 219, 83.](https://link.springer.com/article/10.1007/s11214-023-01031-4)\n4. [Holt, T. R. et al. (2020). Stability of Jovian Trojans and their collisional families. Monthly Notices of the Royal Astronomical Society 495, 4085.](https://academic.oup.com/mnras/article/495/4/4085/5837576)\n5. [IAU Minor Planet Center, minorplanetcenter.net](http://www.minorplanetcenter.net/db_search/show_object?object_id=12238)\n\n---\n*Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Jupiter Trojans and other dynamical groups › Greek-camp Jupiter Trojans › Lesser Achaean warriors*\n\n*Initially written Oct 21, 2026 · Edited: Oct 25, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [ "https://www2.boulder.swri.edu/~buie/recon/trojans/12238_Actor_20250403192059.html", "https://www.boulder.swri.edu/~buie/recon/trojans/12238_Actor_20260523100721.html" ], "url": "https://www.edgepedia.org/12238-actor", "markdown_url": "https://www.edgepedia.org/12238-actor.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"12238 Actor\", Edgepedia (EdgeChat), https://www.edgepedia.org/12238-actor. Edgepedia Community License 1.0.", "credit_md": "\"[12238 Actor](https://www.edgepedia.org/12238-actor)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/12238-actor](https://www.edgepedia.org/12238-actor). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"12238 Actor\", Edgepedia (EdgeChat), https://www.edgepedia.org/12238-actor. Edgepedia Community License 1.0.", "speakable": "12238 Actor is a Jupiter Trojan asteroid discovered by Eric Elst and Guido Pizarro in 1987 at the La Silla Observatory in Chile, named after Actor of Greek mythology." }