Earth’s First Trojan Asteroid Discovered by NASA’s WISE

A “Trojan” asteroid has been discovered sharing Earth’s solar orbit by astronomers studying observations taken by NASA’s Wide-field Infrared Survey Explorer (WISE) mission.

Earth's first Trojan asteroid

Trojans are asteroids that are gravitationally bound to a planet, but are not moons, because they do not orbit the planet. Instead they orbit one of the two stable points in front of or behind the planet, called Lagrangian points (L4 and L5 to be precise).

In our solar system, Trojans are fairly common. Some share orbits with Neptune, Mars and Jupiter. Two of Saturn’s moons also share orbits with Trojans.

It has been predicted by scientists that the Earth should have Trojans, but they have been difficult to find because they are quite small and appear near the sun from Earth’s point of view, the sun’s glare making it very difficult to detect them.

The discovery was made by a team lead by Martin Connors of Athabasca University in Canada and was based on the NEOWISE (the Near Earth Object portion of the WISE mission) scans of the entire sky in infrared light from January 2010 to February 2011.

The asteroid is called 2010 TK7 and is roughly 300 meters in diameter. Its orbit around the Lagrange point is very unusual as shown in the video below. On average it is about 80 million kilometers from Earth, but it is predicted that it sometimes comes as close as 24 million kilometers.

There is no risk of such asteroids crashing into the Earth in the foreseeable future since their orbits, although often unusual, are relatively stable. So unless their orbit gets perturbed by another object, they will remain orbiting the Lagrange point for millions of years or more.

Since Earth Trojans are so hard to spot, it’s quite possible that there are a lot more of them. They would be a perfect location to visit and maybe even colonize beyond the Earth-Moon system, before moving on to Mars and beyond.

Image credit: NASA/JPL-Caltech/UCLA
Movie credit: Paul Wiegert, University of Western Ontario, Canada