Astronomers discovered Earth's first Trojan asteroid dubbed "2010 TK7" rotating the sun in earth's orbit. It is 300 meters wide and about 48 million miles from Earth.

Professor Paul Wiegert and a team led by Martin Connors of Athabasca University in Alberta spotted it with NASA's WISE satellite. The asteroid was confirmed in April although it was discovered last year. The brightness of the sun and the daytime sky prevented astronomers from discovering it before.

Professor Paul Wiegert of the University of Western Ontario told The Toronto Star, "The interesting thing is that it is synchronized with the Earth."

The asteroid is "like a dog on a leash", and it is safe as it "never gets particularly close to the Earth, but it doesn't wander too far away. There is a distinct gravitational link."

The Trojan asteroids, named because of the complicated "tango" they perform with planets, were proposed in 1772 and discovered near Jupiter in 1906, this one is the first for Earth.

"We do expect to find more of them," Wiegert said.

And since this particular asteroid never wanders too far, a probe could be sent out which would tell scientists which rare metals are inside the rock.

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Asteroid Earth