Trojan Asteriod

Asteroid (or satellite) that orbits a body at one of the Lagrange points 60º ahead (L4) or behind (L5) a secondary body. Although Trojan asteroids have been discovered for Mars (5, all at L5) and Neptune (2), the term generally refers to the ~1800 asteroids accompanying Jupiter (~60% at L4). Although the Trojans are stabilized at the Lagrangian points by gravitational interactions with Jupiter and the Sun, their actual distribution is elongated along the orbit. Perturbations from other planets (primarily Saturn) cause the Trojans to oscillate around L4 and L5 by 15-20° and inclinations up to 40° to the orbital plane. These oscillations generally take 150-200 years to complete. The absence of Trojans at the Lagrangian points of Saturn most likely results from Jupiter removing them from these stable orbits through gravitational perturbations. Other examples of Trojan bodies in the solar system include daughter satellites that orbit in the Trojan points of the Saturn-Tethys system, and an additional satellite (Helene) which orbits in the forward Trojan point of Saturn and Dione.


Image source: http://astronomy.swin.edu.au/cms/astro/cosmos/T/Trojan+Asteroids.