  Asteroids with satellites are natural laboratories to constrain the formation
and evolution of our solar system. The binary Trojan asteroid (624) Hektor is
the only known Trojan asteroid to possess a small satellite. Based on W.M. Keck
adaptive optics observations, we found a unique and stable orbital solution,
which is uncommon in comparison to the orbits of other large multiple asteroid
systems studied so far. From lightcurve observations recorded since 1957, we
showed that because the large Req=125-km primary may be made of two joint
lobes, the moon could be ejecta of the low-velocity encounter, which formed the
system. The inferred density of Hektor's system is comparable to the L5 Trojan
doublet (617) Patroclus but due to their difference in physical properties and
in reflectance spectra, both captured Trojan asteroids could have a different
composition and origin.
