617 Patroclus was the second Jovian trojan to be discovered, by August Kopff in 1906. Patroclus lies at Jupiter's trailing Lagrangian point (L5). It is the only trojan of Jupiter in the "Trojan camp" to be named after a Greek character because the naming conventions for the Trojan asteroids were not adopted until after Patroclus was named.

 

In 2001 it was discovered that Patroclus is actually a binary asteroid. The larger component retains the name Patroclus while the smaller has been named Menoetius, with the provisional designation S/2001 (617) 1.

 

In January 2006 it was announced that Patroclus and Menoetius are more likely to be dirt-covered ice balls than rocky rubble piles, as previously supposed. This interpretation supports a theory put forward in 2005 that the Trojans are effectively frozen comets captured by Jupiter some 650 million years after the giant planets formed.¹

 

diameter	105 km
density	0.8 g/cm³
albedo	0.047
rotational period	40 hours
semimajor axis	5.228 AU
perihelion	4.506 AU
aphelion	5.950 AU
eccentricity	0.138
inclination	22.03°
period	11.95 years
other designations	1906 VY, 1941 XC, and 1962 NB

 

Reference

1. Marchis, F., et al. "A low density of 0.8 g cm^-3 for the Trojan binary asteroid 617 Patroclus." Nature, vol 439, p 563, 2006.