Trojan (astronomy),

In astronomy, the word trojan refers to a minor planet or natural satellite (moon) that shares an orbit with a larger planet or moon, but does not collide with it because it orbits around one of the two Lagrangian points of stability, L4 and L5, which lie 60° ahead of and behind the larger body.

The term originally referred to the trojan asteroids orbiting around Jupiter's Lagrangian points, and asteroids at the Lagrangian points of other planets may be called Lagrangian asteroids. Subsequently objects have been found orbiting the Lagrangian points of Neptune and Mars. In addition, trojan moons are known to orbit the Lagrangian points of two of Saturn's mid-sized moons.

The term trojan asteroid usually refers specifically to Jupiter trojans, which are thought to be as numerous as the asteroids of the main belt.

5261 Eureka, 1998 VF31, 1999 UJ7, and 2007 NS2 are Mars trojans.

Seven Neptune trojans are known, but they are believed to outnumber the Jupiter trojans by an order of magnitude.

(source:wikipedia)