Astronomy: General

A Dictionary of Astronomy The Columbia Encyclopedia, 6th ed. Further reading

Trojan asteroid

A Dictionary of Astronomy | 1997 | Copyright

Trojan asteroid A member of one of two groups of asteroids, at a mean distance of 5.2 AU from the Sun, which share the orbit of Jupiter. They lie clustered around the leading (L₄) and following (L₅) Lagrangian points, 60 ° ahead of and behind Jupiter. Perturbations by other planets cause the Trojans to oscillate along the orbit of Jupiter about 45–80 ° from the planet, taking 150–200 years per cycle. The first Trojan to be discovered was Achilles in 1906. Over 2000 Trojan asteroids are now known, 55 % in the leading (L₄) group. In 1990 the first Martian Trojan, (5261) Eureka, was discovered in the L₅ region of Mars's orbit, and in 2001 the first Neptunian Trojan (2001 QR₃₂₂) was discovered at Neptune's leading Lagrangian point.

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Trojan asteroids

The Columbia Encyclopedia, 6th ed. | 2011 | Copyright

Trojan asteroidsasteroids 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 .

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Free newspaper and magazine articles

	WISE mission finds first Trojan asteroid sharing Earth's orbit. News Wire article from: Philippines News Agency; 7/28/2011
	Earth's first Trojan asteroid discovered. News Wire article from: Philippines News Agency; 7/28/2011
	By Jupiter, the asteroids are coming. Newspaper article from: Daily Mail (London); 1/2/1997