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ncoming Asteroid Under Close Watch
Irene Klotz, Discovery News
URLﾘﾝｸ(dsc.discovery.com)
April 13, 2009 -- Exactly 20 weeks from today, an asteroid about the size of a 25-story
building will come closer to Earth than the networks of communications satellites orbiting
the planet. The chance of an impact are extremely remote -- only about 1 in 45,000 --
but the asteroid, named Apophis, will be back. Analysis of the asteroid's orbit show it will
return to Earth seven years later. （中略） The telescope array, funded by the Air Force
Research Laboratories, combines small mirrors with massive digital cameras to image
the entire sky several times a month. Pan-STARRS supplements ongoing NASA-funded
efforts to survey 90 percent of near-Earth objects bigger than 140 meters, or 459 feet.
"As things get bigger, the amount of devastation goes up dramatically," Kaiser said, but
so too does the length of time between occurrences. A half-mile diameter object
impacting Earth likely would cause a global catastrophe, but these events happen every
couple of million years or so, Kaiser said. （以下略）