Asteroid Stalks Earth in Weird Horseshoe-Shaped Orbit

A newfound asteroid has been discovered to be trailing Earth on an oddball course: an orbit that looks a lot like a horseshoe.The space rock, called asteroid 2010 SO16, has been following Earth as our planet orbits the sun for at least 250,000 years and is up to 1,312 feet 400 meters wide, scientists said. It was initially spotted by NASA's WISE infrared space observatory. [Photos of asteroid 2010 SO16 and its orbit]"Its average distance from the sun is identical to that of the Earth, but what really impressed me at the time was how Earth-like its orbit was," said Apostolos Christou, an astronomer at the Armagh Observatory in the United Kingdom, who led the study that pinned down the asteroid's orbit. Christou and study co-author David Asher found that asteroid 2010 SO16 takes about 175 years to travel from one end of its orbit to another before doubling back. In diagrams, the asteroid's orbit resembles a giant letter "C" with the Earth ticked between the endpoints. [Photos: Asteroids in Deep Space]Currently, the asteroid is at a point in its orbit that brings it near the horseshoe's tip that trails the Earth. But despite its apparent attachment to Earth's orbit, the asteroid poses no risk of smacking our planet."This asteroid is terraphobic," Christou said. "It keeps well away from the Earth. So well, in fact, that it has likely been in this orbit for several hundred thousand years, never coming closer to our planet than 50 times the distance to the moon." The average distance between the Earth and the moon is about 238,000 miles 382,900 kilometers.

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