Trojan asteroids

Although the vast majority of asteroids (minor planets and rocky debris) in the Solar System orbit the Sun in a belt between Mars and Jupiter, there are many that do not. In particular, there are about 6,000 that can be found in the same orbit as Jupiter, either 60 degrees “ahead of ” or “behind” the giant planet.

These areas are known as “Lagrangian points”, their significance being that this is where the gravitational influences of the Sun and Jupiter cancel each other out. The asteroids can therefore have stable orbits.

These have been named “Trojans” because the larger asteroids have been given names derived from the names of warriors in the Homeric Trojan wars. The two groups are either “Greeks” or “Trojans”, but these objects, locked in their orbits as they are, are fated never to meet in combat.

The name Trojan asteroid has been given to objects that are similarly placed in orbits ahead of or behind other major planets. Mars, Uranus and Neptune are all known to have Trojans, and in 2011 one was discovered in Earth’s orbit, this having the somewhat unromantic name of 2010 TK.

© John Welford