Trojan asteroids, asteroids that revolve about the sun in the same orbit as a planet, occupying stable positions (known as Lagrangian points) either about 60° ahead of the planet in the orbit or about 60° behind it. Such asteroids were first discovered (1906) in Jupiter's orbit. In 1990, a similar asteroid, Eureka, was found in the orbit of Mars, and several others have since been discovered. Similar asteroids also have been found in Neptune's orbit since 2001, and a Trojan asteroid in earth's orbit was confirmed in 2011.
The Trojan asteroids represent one possible special solution to the famous three-body problem (see also celestial mechanics), with each group forming an equilateral triangle with the planet whose orbit they share and the sun. Some Trojan asteroids are composed of ice and dirt, rather than rock, making it possible that they are captured comets. The first Trojan asteroid discovered was Achilles, observed by the German astronomer Max Wolf; all of Jupiter's Trojan asteroids are named for heroes of the Trojan War.