The Jupiter Trojans, commonly called Trojans or Trojan
asteroids, 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 discovered, 588 Achilles, was spotted in 1906 by the
German astronomer Max Wolf. A total of 5,253 Jupiter Trojans
have been found as of March 2012[update]. The term "Trojan"
derives from the fact that, by convention, they are each named
after a mythological figure from the Trojan War. The total
number of Jupiter Trojans larger than 1 km in diameter is
believed to be about 1 million, approximately equal to the
number of asteroids larger than 1 km in the asteroid belt. Like
main-belt asteroids, Trojans form families.