俄罗斯发生陨石爆炸事故 500多人受伤
The meteor explosion over Russia that injured more than 500 people and damaged hundreds of buildings was not caused by an asteroid zooming close by the Earth today (Feb.15), a NASA scientist says.
俄罗斯近日（2月15日）发生的陨石爆炸已造成超过500人受伤，毁坏了数百座建筑。美国宇航局一位科学家表示，这次陨石爆炸并不是由小行星撞击地球引起的。
The trail of a falling object is seen above the Urals city of Chelyabinsk February 15, 2013, in this picture.
NASA asteroid（小行星） expert Don Yeomans, head of the agency's Near-Earth Object Program Office, told SPACE.com that the object which exploded over a thinly inhabited stretch of eastern Europe today was most likely an exploding fireball known as a bolide（火流星）.
More than 500 people were injured, mostly by glass cuts when windows shattered during the blast, according to the Russian Emergency Ministry.
"If the reports of ground damage can be verified, it might suggest an object whose original size was several meters in extent before entering the atmosphere, fragmenting and exploding due to the unequal pressure on the leading side vs the trailing side (it pancaked and exploded)," Yeomans told SPACE.com in an email. "It is far too early to provide estimates of the energy released or provide a reliable estimate of the original size."
Yeoman stressed that the bolide event was likely not associated at all with the incoming asteroid 2012 DA14, which will fly within 17,200 miles (27,000 kilometers) of Earth when it passes safely by our planet today.
"The asteroid will travel south to north," Yeomans said. "The bolide trail was not south to north and the separation in time between the fireball and 2012 DA14 close approach is significant."
Asteroid 2012 DA14 is 150 feet (45 meters) wide — about half the size of a football field — and will make its closest approach to Earth at 2:24 p.m. EST (1924 GMT) when it passes over Indonesia. It will be about 5,000 miles (8,046 kilometers) closer to Earth than the communications satellites circling the planet in geosynchronous orbits（同步轨道）.
NASA scientists and professional and amateur astronomers around the world have been tracking asteroid 2012 DA14 since it was first discovered by a team of amateurs in February 2012. Not only does the asteroid pose no threat to Earth during today's flyby, but it will not hit Earth for the foreseeable future, NASA scientists have said.