Astronomy:12238 Actor

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12238 Actor
Discovery[1]
Discovered byE. W. Elst
G. Pizarro
Discovery siteLa Silla Obs.
Discovery date17 December 1987
Designations
(12238) Actor
Pronunciation/ˈæktɔːr/
Named afterActor (Greek mythology)[1]
1987 YU1 · 1986 WW8
Minor planet categoryJupiter trojan[1][2]
Greek[3] · background[4]
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc31.47 yr (11,494 d)
|{{{apsis}}}|helion}}5.8135 AU
|{{{apsis}}}|helion}}4.5361 AU
5.1748 AU
Eccentricity0.1234
Orbital period11.77 yr (4,300 d)
Mean anomaly245.58°
Mean motion0° 5m 1.32s / day
Inclination21.091°
Longitude of ascending node227.59°
177.30°
Jupiter MOID0.4056 AU
TJupiter2.8520
Physical characteristics
Mean diameter30.25±4.84 km[5]
36.78 km (calculated)[6]
Rotation period7.284 h[7]
Geometric albedo0.057 (assumed)[6]
0.092±0.017[5]
C (assumed)[6]
Absolute magnitude (H)10.80[5]
10.9[1][2][6]


12238 Actor /ˈæktɔːr/ is a Jupiter trojan from the Greek camp, approximately 30 kilometers (19 miles) in diameter. It was discovered on 17 December 1987, by astronomers Eric Elst and Guido Pizarro at the La Silla Observatory in northern Chile.[1] The dark Jovian asteroid has a rotation period of 7.3 hours.[6] It was named after Actor, father of the heroes Eurytus and Cteatus from Greek mythology.[1]

Orbit and classification

As all Jupiter trojans, Actor is in a 1:1 orbital resonance with Jupiter. It is located in the leading Greek camp at the Gas Giant's L4 Lagrangian point, 60° ahead on its orbit (see Trojans in astronomy).[3] It is also a non-family asteroid of the Jovian 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 an eccentricity of 0.12 and an inclination of 21° with respect to the ecliptic.[2]

The body's observation arc begins with its first observation as 1986 WW8 at the Kiso Observatory in November 1986, or 13 months prior to its official discovery observation at La Silla.[1]

Naming

This minor planet was named from Greek mythology after Actor (son of Phorbas and Hyrmine), the alleged father of the twin brothers Eurytus and Cteatus, who beat Nestor, king of Pylos, in a chariot race.[1] The official naming citation was published by the Minor Planet Center on 6 January 2003 (M.P.C. 47300).[8]

Physical characteristics

Actor is an assumed C-type asteroid, while the majority of larger Jupiter trojans are D-types.[6]

Rotation period

In 2007, a rotational lightcurve of Actor was obtained from photometric observations at the Sierra Nevada Observatory, using its 1.5-meter telescope. Lightcurve analysis gave a rotation period of 7.284 hours with a brightness variation of 0.30 magnitude ({{{1}}}).[7] The same group also published a period determination of 7.28±0.02 hours with an amplitude of 0.33 magnitude in 2010.[6][9]

In July and August 2015, observations by the Kepler space telescope during its K2 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 ({{{1}}}).[10][11]

Diameter and albedo

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

100+ largest Jupiter trojans

References

  1. ↑ Jump up to: 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "12238 Actor (1987 YU1)". Minor Planet Center. https://www.minorplanetcenter.net/db_search/show_object?object_id=12238. Retrieved 5 July 2018. 
  2. ↑ Jump up to: 2.0 2.1 2.2 2.3 "JPL Small-Body Database Browser: 12238 Actor (1987 YU1)". Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012238. Retrieved 5 July 2018. 
  3. ↑ Jump up to: 3.0 3.1 "List of Jupiter Trojans". Minor Planet Center. 1 July 2018. https://www.minorplanetcenter.net/iau/lists/JupiterTrojans.html. Retrieved 5 July 2018. 
  4. ↑ Jump up to: 4.0 4.1 "Asteroid (12238) Actor – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. https://newton.spacedys.com/astdys/index.php?n=12238&pc=1.1.6. 
  5. ↑ Jump up to: 5.0 5.1 5.2 5.3 Grav, T.; Mainzer, A. K.; Bauer, J. M.; Masiero, J. R.; Nugent, C. R. (November 2012). "WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy". The Astrophysical Journal 759 (1): 10. doi:10.1088/0004-637X/759/1/49. Bibcode: 2012ApJ...759...49G.  (online catalog)
  6. ↑ Jump up to: 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 "LCDB Data for (12238) Actor". Asteroid Lightcurve Database (LCDB). http://www.minorplanet.info/PHP/generateOneAsteroidInfo.php?AstInfo=12238%7CActor. Retrieved 5 July 2018. 
  7. ↑ Jump up to: 7.0 7.1 Duffard, R. D.; Melita, M.; Ortiz, J. L.; Licandro, J.; Williams, I. P.; Jones, D. (December 2007). "Light-Curve Survey of the Trojan Asteroids". Asteroids 1405: 8187. Bibcode: 2008LPICo1405.8187D. https://www.lpi.usra.edu/meetings/acm2008/pdf/8187.pdf. Retrieved 5 July 2018. 
  8. ↑ "MPC/MPO/MPS Archive". Minor Planet Center. https://www.minorplanetcenter.net/iau/ECS/MPCArchive/MPCArchive_TBL.html. Retrieved 5 July 2018. 
  9. ↑ Melita, M. D.; Duffard, R.; Williams, I. P.; Jones, D. C.; Licandro, J.; Ortiz, J. L. (June 2010). "Lightcurves of 6 Jupiter Trojan asteroids". Planetary and Space Science 58 (7–8): 1035–1039. doi:10.1016/j.pss.2010.03.009. Bibcode: 2010P&SS...58.1035M. 
  10. ↑ Ryan, Erin Lee; Sharkey, Benjamin N. L.; Woodward, Charles E. (March 2017). "Trojan Asteroids in the Kepler Campaign 6 Field". The Astronomical Journal 153 (3): 12. doi:10.3847/1538-3881/153/3/116. Bibcode: 2017AJ....153..116R. 
  11. ↑ Szabó, Gy. M.; Pál, A.; Kiss, Cs.; Kiss, L. L.; Molnár, L.; Hanyecz, O. et al. (March 2017). "The heart of the swarm: K2 photometry and rotational characteristics of 56 Jovian Trojan asteroids". Astronomy and Astrophysics 599: 13. doi:10.1051/0004-6361/201629401. Bibcode: 2017A&A...599A..44S. 

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