Trojan asteroid discovered in Earth orbit

Astronomers have discovered the first Trojan asteroid sharing Earth's orbit around the Sun, ABC reported.

Trojans are asteroids locked in stable orbits by a gravitational balancing act between a planet and the Sun. They have previously been discovered accompanying Neptune, Jupiter and Mars.

Scientists led by Dr Martin Connors from Athabasca University in Canada suspected they may also be in stable positions orbiting with the Earth.

But Connors says finding an 'Earth-bound' Trojan is difficult because its location can only be seen from Earth in daylight.

"When you look out towards Jupiter you've got no real problems picking up its Trojans because they're in the night sky for us most of the time", says Connors.

"But for our own Trojans, they're kind of near to the Sun, so they're the sort of thing you'll only see for an hour or so in the evening and in the morning, that's your only opportunity to look for them."

"That's why none have been found before."

Connors says the launch of NASA's Wide-field Infrared Survey Explorer spacecraft (WISE) in 2009 changed all that.

"WISE looked at the infrared light coming from all over the sky and was particularly good at detecting asteroids, finding about 150,000 of them, including 500 which come near the Earth."

By examining the orbits of these objects in the WISE data, Connors and colleagues identified a small asteroid called 2010 TK7 as a probable Earth Trojan. The researchers then used ground-based telescopes to confirm the sighting, calculating that it's been in a stable orbit with Earth for more than 10,000 years.

Their finding appears today in the journal Nature.