Trojan (astronomy)

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Trojan asteroids of Jupiter (coloured green) in front of and behind Jupiter along its orbital path. Also shown is the main asteroid belt between the orbits of Mars and Jupiter (white), and the Hilda family of asteroids (brown)

In astronomy, the adjective '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.^[1] 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^[2].
• Six Neptune trojans^[3] are known, but they are expected to outnumber the Jupiter trojans by an order of magnitude.

[edit] References

1. ^ Robert J. Whiteley and David J. Tholen, "A CCD Search for Lagrangian Asteroids of the Earth–Sun System", Icarus 136:1, November 1998:154-167
2. ^ "List of Martian Trojans". http://cfa-www.harvard.edu/iau/lists/MarsTrojans.html. Retrieved on 2007-08-31. 
3. ^ "List of Neptune Trojans". http://cfa-www.harvard.edu/iau/lists/NeptuneTrojans.html. Retrieved on 2007-08-31. 

[edit] See also

• Hilda family of asteroids
• Lagrangian point
• List of Mars Trojan asteroids
• List of objects at Lagrangian points
• Trojan moon
• Trojan planet

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