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]
Small Ennomos family
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]
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]
Rotation period
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]
Diameter and albedo
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]
100+ largest Jupiter trojans
Largest Jupiter Trojans by survey(A) (mean-diameter in kilometers; YoD: Year of Discovery)
Note: missing data was completed with figures from the JPL SBDB (query) and from the LCDB (query form) for the WISE/NEOWISE and SIMPS catalogs, respectively. These figures are given in italics. Also, listing is incomplete above #100.
Notes
^ abcLightcurve plots of (4709) Ennomos from Feb 2015, Dec 2015/Jan 2016 and Feb 2017 by Daniel Coley and Robert Stephens at the Center for Solar System Studies (U81). Quality code is 3/3-/2 (lightcurve rating at CS3). Summary figures at the LCDB and CS3.
^ abcdTedesco, E. F.; Noah, P. V.; Noah, M.; Price, S. D. (October 2004). "IRAS Minor Planet Survey V6.0". NASA Planetary Data System – IRAS-A-FPA-3-RDR-IMPS-V6.0. 12: IRAS-A-FPA-3-RDR-IMPS-V6.0. Bibcode:2004PDSS...12.....T. Retrieved 15 June 2018.
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