1208 Troilus

Hubble Space Telescope image of Troilus taken in 2012
Discovery[1]
Discovered by	K. Reinmuth
Discovery site	Heidelberg Obs.
Discovery date	31 December 1931
Designations
MPC designation	(1208) Troilus
Pronunciation	/ˈtroʊɪləs, ˈtrɔɪləs/[2][3]
Named after	Troilus (Greek mythology)[4]
Alternative designations	1931 YA · 1965 WK
Minor planet category	Jupiter trojan[1][5][6] Trojan[7][8] · background[8]
Adjectives	Troilian
Orbital characteristics[5]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	86.40 yr (31,557 d)
Aphelion	5.7305 AU
Perihelion	4.7712 AU
Semi-major axis	5.2509 AU
Eccentricity	0.0913
Orbital period (sidereal)	12.03 yr (4,395 d)
Mean anomaly	189.17°
Mean motion	0° 4m 54.84s / day
Inclination	33.542°
Longitude of ascending node	48.546°
Argument of perihelion	296.06°
Jupiter MOID	0.001 AU
TJupiter	2.6590
Physical characteristics
Mean diameter	100.48±1.10 km[9] 103.31 km (derived)[6] 103.34±3.9 km[10] 111.36±2.36 km[11]
Synodic rotation period	24 h[12] 56.17±0.07 h[13] 63.8±0.5 h[14]
Geometric albedo	0.037±0.002[11] 0.0397 (derived)[6] 0.041±0.006[9] 0.0419±0.003[10]
Spectral type	FCU (Tholen)[5][6] C0 (Barucci) U–B = 0.314±093[5] B–V = 0.750±0.050[15] V–R = 0.380±0.030[15] V–I = 0.740±0.020[6]
Absolute magnitude (H)	8.99[1][5][10][11] 9.05[6][12] 9.08[9][16]

1208 Troilus /ˈtroʊɪləs/ is a large and notably inclined Jupiter trojan from the Trojan camp, approximately 103 kilometers (64 miles) in diameter. It was discovered on 31 December 1931, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southern Germany.^[1] The unusual F-type asteroid belongs to the largest Jupiter trojans and has a long rotation period of 56.2 hours.^[6] It was named after the Trojan prince Troilus, who was killed by Achilles.^[4]

Troilus is a dark Jovian asteroid orbiting in the trailing Trojan camp at Jupiter's L₅ Lagrangian point, 60° behind its orbit in a 1:1 resonance (see Trojans in astronomy). It is also a non-family asteroid of the Jovian background population.^[8][17]

It orbits the Sun at a distance of 4.8–5.7 AU once every 12 years (4,395 days; semi-major axis of 5.25 AU). Its orbit has an eccentricity of 0.09 and a high inclination of 34° with respect to the ecliptic.^[5] The body's observation arc begins with its official discovery observation at Heidelberg in December 1931.^[1]

In the Tholen classification, Troilus has an ambiguous and unusual spectrum, closest to that of an F-type and somewhat similar to a common C-type asteroid (FCU).^[5][6] It has also been characterized as a carbonaceous C-type in the Barucci taxonomy (C0-type).^[17]

In April 2007, a rotational lightcurve of Troilus was obtained from photometric observations by Lawrence Molnar at the Calvin-Rehoboth Robotic Observatory (G98) in New Mexico. Lightcurve analysis gave a rotation period of 56.17±0.07 hours with a brightness variation of 0.20±0.02 magnitude (U=2).^[6][13] While not being a slow rotator, Troilus has a significantly longer period than most asteroids, and one of longest of all larger Jupiter trojans.

The period also supersedes previous observations made by Linda French with the 0.9-meter SMARTS telescope at Cerro Tololo in the 1980s and by Federico Manzini at the Sozzago Astronomical Station (A12), which gave a period of 24 and 63.8 hours, respectively (U=2/1).^[12][14]

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Troilus measures between 100.48 and 111.36 kilometers in diameter and its surface has an albedo between 0.037 and 0.0419.^[9][10][11] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0397 and a diameter of 103.31 kilometers based on an absolute magnitude of 9.05.^[6]

This minor planet was named from Greek mythology after the young Trojan prince Troilus, the son of King Priam (also see 884 Priamus), who in a medieval legend loved Cressida (see 548 Kressida) and lost her to Diomedes (see 1437 Diomedes). Troilus was killed by Achilles (see 588 Achilles) in the Trojan War. The official naming citation was published by Paul Herget in The Names of the Minor Planets in 1955 (H 112).^[4]

• Asteroid Lightcurve Database (LCDB), query form (info Archived 16 December 2017 at the Wayback Machine)
• Dictionary of Minor Planet Names, Google books
• Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend
• Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
• 1208 Troilus at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 1208 Troilus at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters