CNN Europe CNN Asia Languages Spanish Portuguese German Italian Korean Arabic Japanese On CNN TV Transcripts Headline News CNN International ... Special Reports SERVICES Video E-Mail Services CNNtoGO SEARCH Web CNN.com Threat of killer asteroids downgraded Hits that could destroy cities predicted every 1,000 years By Richard Stenger
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RELATED Nature University of Western Ontario University of Arizona (CNN) Space boulders big enough to wipe out a major city slam into the Earth about once every 1,000 years, much less frequently than previously thought, scientists said Wednesday. The revised calculations come from an unprecedented examination of years of data from U.S. Defense Department satellites that scour the ground for nuclear explosions. Previous ground-based observations had suggested that asteroids or comets of comparable size pound the planet once every two or three centuries. "This new method of obtaining information redefines our range of knowledge about how and when asteroids may hit the Earth," said University of Western Ontario astronomer Peter Brown, lead author of a report in the November 21 edition of the journal Nature. During the past 8.5 years, the military orbiters spotted almost 300 light bursts high in the atmosphere caused by the explosions of meteors between one and 10 meters (3.3 and 33 feet) in diameter. | |
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