A robotic NASA explorer uncovered evidence of a "Trojan asteroid" flying in the same orbit around the sun as Earth, but the space rock is no threat to the planet, officials said.
Trojans are asteroids that fly in the same orbits as planets. Since they constantly lead or follow, they can never collide with the planet they share an orbit with.
In this case, instruments aboard NASA's Wide-field Infrared Survey Explorer scanned the entire sky with infrared instruments during a 13-month period that began in January 2010. Astronomers studying the observations discovered the first known Trojan following Earth. Neptune, Mars and Jupiter have Trojans. So do two of Saturn's moons.
Asteroid 2010 TK7 is about 1,000 feet in diameter. It's now flying about 50 million miles ahead of Earth, and it is not expected to come closer to Earth than 15 million miles in the next 100 years.
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NASA's WISE spacecraft was launched aboard a United Launch Alliance Delta II rocket in December 2009 from Vandenberg Air Force Base in California.