4709 Ennomos

Shape model of Ennomos from its lightcurve
Discovery [1]
Discovered by	C. Shoemaker
Discovery site	Palomar Obs.
Discovery date	12 October 1988
Designations
MPC designation	(4709) Ennomos
Pronunciation	/ˈɛnəməs/[2]
Named after	Ennomus [1] (or Ennomos) (Greek mythology)
Alternative designations	1988 TU2 · 1954 UM1 1977 UT2
Minor planet category	Jupiter trojan [1][3][4] · Trojan [5][6] Ennomos [7] · background [6]
Adjectives	Ennomian
Orbital characteristics [3]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	66.80 yr (24,398 d)
Aphelion	5.3542 AU
Perihelion	5.1345 AU
Semi-major axis	5.2443 AU
Eccentricity	0.0209
Orbital period (sidereal)	12.01 yr (4,387 d)
Mean anomaly	204.60°
Mean motion	0° 4m 55.56s / day
Inclination	25.452°
Longitude of ascending node	253.12°
Argument of perihelion	86.215°
Jupiter MOID	0.0877 AU
TJupiter	2.8050
Physical characteristics
Mean diameter	80.03±2.17 km[8] 80.85±4.3 km[9] 81.23 km (derived)[4] 91.43±0.78 km[10]
Synodic rotation period	11.12±0.01 h[11] 12.267±0.002 h[12][a] 12.269±0.001 h[13][a] 12.2696 h[4] 12.271±0.001 h[14][a] 12.275±0.008 h[15]
Geometric albedo	0.0744±0.009[9] 0.077±0.009[10] 0.078±0.005[8] 0.0972 (derived)[4]
Spectral type	C (assumed)[4] B–V = 0.670±0.060[16] V–R = 0.350±0.040[16] V–I = 0.690±0.017[4]
Absolute magnitude (H)	8.5[1][3] 8.6[4][10] 8.62±0.57[17] 8.90[8][9]

4709 Ennomos /ˈɛnəməs/ is a large Jupiter trojan from the Trojan camp and the namesake of the small Ennomos family, approximately 81 kilometers (50 miles) in diameter. It was discovered on 12 October 1988, by American astronomer Carolyn Shoemaker at the Palomar Observatory in California.^[1] The relatively bright and possibly elongated Jovian asteroid belongs to the 40 largest Jupiter trojans and has a rotation period of 12.3 hours.^[4] It was named after Ennomus (Ennomos), a Trojan warrior killed by Achilles.^[1]

Ennomos is a 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).^[5]

It orbits the Sun at a distance of 5.1–5.4 AU once every 12 years (4,387 days; semi-major axis of 5.24 AU). Its orbit has an eccentricity of 0.02 and an inclination of 25° with respect to the ecliptic.^[3] The body's observation arc begins with a precovery taken at Palomar in August 1951, more than 37 years prior to its official discovery observation.^[1]

This Jupiter trojan is also the namesake of the Ennomos family (009),^[7] a small Jovian asteroid family with 30 known members.^[18] The family was first identified by Jakub Rozehnal and Miroslav Brož in 2011.^[19] It also includes 1867 Deiphobus, one of the largest Jovian trojans.^[18]

As the existence of this family is not well established, Ennomos is still considered part of the Jovian background population by another HCM-analysis (Knezevic and Milan).^[6] It is speculated that Ennomos might be an unrelated interloper in its own family rather than its parent body.^[19] As of 2018, only a few families have been identified among the Jovian asteroids. These are the Hektor family, the Eurybates family, and the Arkesilaos family as well as two unnamed families, 006 and 010).^[18]

This minor planet was named by the discoverer from Greek mythology after the Trojan warrior Ennomus (Ennomos), who was one of many Trojans killed by Achilles in the waters of the River Skamander.^[1] The official naming citation was published by the Minor Planet Center on 28 April 1991 (M.P.C. 18144).^[20]

Ennomos is an assumed C-type asteroid. Its V–I color index of 0.69 is untypically low compared to most other large Jupiter trojans.^[4]

In December 1990, a rotational lightcurve of Ennomos was obtained by Italian astronomers Stefano Mottola and Mario Di Martino using the 1.52-meter Loiano Telescope at the Observatory of Bologna in Italy. Lightcurve analysis gave a well-defined rotation period of 12.275 hours with a relatively high brightness amplitude of 0.47 magnitude (U=3), indicative of a non-spherical, elongated shape.^[4][15]

Between 2015 and 2017, photometric observations by Daniel Coley and Robert Stephens at the Center for Solar System Studies, California, gave several concurring periods of 12.267, 12.269 and 12.271 with an amplitude between 0.43 and 0.46 magnitude (U=3/3/3).^[12][13][14] This also supersedes a period form Stephens taken at the GMARS Observatory (G79) in September 2011.^[11]

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, Ennomos measures between 80.03 and 91.43 kilometers in diameter and its surface has an albedo between 0.077 and 0.078.^[8][9][10] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0972 and a diameter of 81.23 kilometers based on an absolute magnitude of 8.6.^[4] Also, Rozehnal and Brož cite a high visual albedo of approximately 0.15 in their publication.^[19]

• Long-term evolution of asteroid families among Jovian Trojans, Jakub Rozehnal and Miroslav Brož (2014)
• Lightcurve Database Query (LCDB), at www.minorplanet.info
• Dictionary of Minor Planet Names, Google books
• Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
• 4709 Ennomos at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 4709 Ennomos at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters