Trojan Asteroids | Universe Today

Written by Jerry Coffey

Trojan asteroids are a very large group of asteroids that share an orbit with Jupiter. Each of the Trojans liberates around one of two of the Lagrangian points L4 or L5 which are 60° ahead of and behind the planet. The first Trojan was discovered in 1906. There are now 2,909 known Trojan asteroids. Some of the Trojan asteroids are composed of ice and dirt, rather than rock, making it possible that they are captured comets. Each of the Trojans are named for a hero from the Trojan War.

The total number of Trojan asteroids larger than 1 km is believed to be about 1 million. That is just about the same number of asteroids that are believed to be in the main belt. Trojans are thought to have been captured into their orbits during the early stages of the Solar System's formation or slightly later. The total mass of the Trojans is estimated at 0.0001 of the mass of Earth or one-fifth of the mass of the main asteroid belt. The largest of the Trojan asteroids is 624 Hektor with a radius of 102 km. It is thought that the smallest of the Trojans are simply what remains from the collisions of larger Trojans.

Jupiter is no longer the only planet with Trojan asteroids trailing or leading in its orbit. Neptune is known to have 4 Trojans. The four are leading Neptune, so that should put them on the Lagrangian point of L4. Evidence suggests that as telescopes become more powerful, more Trojans will be found around Neptune and possibly planets further from the Sun. One of the new Trojans has a much more steeply inclined orbit than the others. This helps to suggest that there are many more such Trojans, each of them having a complex and dynamic orbit with in the belt. "The discovery of the one tilted Neptune Trojan implies that there may be many more far from the solar system plane than near the plane, and that the Trojans are really a 'cloud' or 'swarm' of objects co-orbiting with Neptune." according to Chadwick Trujillo of the Gemini Observatory.

Our current technology can not tell us everything that we want to know about the universe, but we are rapidly advancing. In the year 2000 there were only 237 Trojan asteroids known, by 2003 there were 1,600 and by 2009 there were 2,909. The rate of discovery tells us that we have only begun to scratch the surface of our knowledge about Trojans. The discovery of more Trojans around other planets just reinforces that idea.

There is a great deal of research on the internet about Trojan asteroids, but some of the best is here on Universe Today. Astronomy Cast has a good episode on Lagrangian Points.

Filed under: Astronomy

Tags: Lagrangian points, trojan asteroids