The
Jupiter Trojans are a large group of objects that share the orbit of the planet
Jupiter around the
Sun. Relative to Jupiter, each Trojan
librates around one of the planet's two
Lagrangian points of stability,
L4 and
L5, that respectively lie 60° ahead of and behind the planet in its orbit. Trojan asteroids are distributed in two elongated, curved regions around these Lagrangian points with an average
semi-major axis of about 5.2 AU. The first Trojan,
588 Achilles, was discovered in 1906 by the German astronomer
Max Wolf. A total of 2,909 Jupiter Trojans have been found as of January 2009
. The name "Trojans" derives from the fact that, by convention, they each are named after a mythological figure from the
Trojan War. The total number of Jupiter Trojans larger than 1 km is believed to be about
1 million, approximately equal to the number of asteroids larger than 1 km in the
main asteroid belt. Like main belt asteroids, Trojans form
families. Jupiter Trojans are dark bodies with reddish, featureless
spectra. No firm evidence of the presence of
water,
organic matter or other chemical compounds has been obtained. The Trojans' densities (as measured by studying
binaries or rotational lightcurves) vary from 0.8 to 2.5 g·cm
−3. Trojans are thought to have been captured into their orbits during the early stages of the
formation and evolution of the Solar System or slightly later, during the
migration of giant planets.
