This asteroid orbits the Sun at a distance of 5.0–5.5 AU once every 12 years and 1 month (4,400 days; semi-major axis of 5.26 AU). Its orbit has an eccentricity of 0.05 and an inclination of 17° with respect to the ecliptic.[3] The body's observation arc begins with its first observation as 1967 GN1 at El Leoncito in April 1967, nearly 33 years prior to its official discovery observation at Socorro.[1]
In November 2011, a rotational lightcurve of Pheidas was obtained from photometric observations by Robert Stephens at the Goat Mountain Astronomical Research Station (G79) in collaboration with Linda French at Illinois Wesleyan University and Daniel Coley at the Trojan Station of Center for Solar System Studies (U81), as well as Ralph Megna and Lawrence Wasserman. Lightcurve analysis gave a rotation period of 8.69 hours with a brightness amplitude of 0.27 magnitude (U=3-).[10] The result supersedes a previous observation from a fragmentary lightcurve that gave a period of only 6.86 hours (U=1).[4][12]
The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and consequently calculates a shorter diameter (due to the higher albedo) of 58.29 kilometers using an absolute magnitude of 9.9.[4] In September 2005, an observed asteroid occultation gave an inconclusive cross-section of 42.0 km × 42.0 km (no fit, but observations sufficiently reliable to derive an astrometric position of the asteroid relative to the star).[7]
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.
^ abFrench, Linda M.; Stephens, Robert D.; Coley, Daniel R.; Megna, Ralph; Wasserman, Lawrence H. (July 2012). "Photometry of 17 Jovian Trojan Asteroids". The Minor Planet Bulletin. 39 (3): 183–187. Bibcode:2012MPBu...39..183F. ISSN1052-8091.