2357 Phereclos /ˈfɛrɪkləs/ is a large Jupiter trojan from the Trojan camp, approximately 95 kilometers (59 miles) in diameter. It was discovered on 1 January 1981, by American astronomer Edward Bowell at the Anderson Mesa Station near Flagstaff, Arizona, in the United States.^[1] The dark and possibly spherical D-type asteroid belongs to the 30 largest Jupiter trojans and has a rotation period of 14.4 hours.^[4] It was named after the shipbuilder Phereclos from Greek mythology.^[1]

Cebriones 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). This Jupiter trojan is also a non-family asteroid of the Jovian background population.^[6][14]

It orbits the Sun at a distance of 5.0–5.4 AU once every 11 years and 11 months (4,344 days; semi-major axis of 5.21 AU). Its orbit has an eccentricity of 0.05 and an inclination of 3° with respect to the ecliptic.^[3] The asteroid was first observed as 1929 SM at Lowell Observatory in September 1929. The body's observation arc begins at Lowell one month later with a precovery taken in October 1929, or more than 51 years prior to its official discovery observation at Anderson Mesa.^[1]

Phereclos is a dark D-type asteroid, according to the Tholen classification, the SDSS-based taxonomy and the survey conducted by Pan-STARRS.^{[3][4][13][14][15]}

In July 2010, a rotational lightcurve of Phereclos was obtained from photometric observations by Stefano Mottola using the 1.2-meter telescope at Calar Alto Observatory in Spain. Lightcurve analysis gave a rotation period of 14.394 hours with a low brightness variation of 0.09 magnitude (U=2+), indicative of a nearly spherical shape.^[4][11]

Between 2010 and 2017, photometric follow-up observations by Robert Stephens at the Center for Solar System Studies, California, gave several, concurring periods of 7.16 (half-period), 14.345 and 14.49 hours.^{[4][10][12][a][b]}

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, Phereclos measures between 94.62 and 98.45 kilometers in diameter and its surface has an albedo between 0.049 and 0.0521.^[7][8][9]

The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is, an albedo of 0.0521 and a diameter of 94.90 kilometers based on an absolute magnitude of 8.94.^[4]

This minor planet was named from Greek mythology after the skilled craftsman and shipbuilder Phereclos (Phereclus; Phereklos), who constructed the ship that Paris used to kidnap Helen. During the Trojan War, he was killed by the Greek hero Meriones.^[1] The official naming citation was published by the Minor Planet Center on 1 August 1981 (M.P.C. 6208).^[17]

• Asteroid Lightcurve Database (LCDB), query form (info Archived 16 December 2017 at the Wayback Machine)
• Dictionary of Minor Planet Names, Google books
• Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
• 2357 Phereclos at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 2357 Phereclos at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters