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Space Rocks Highlight Dangers(九年级阅读)  

2013-02-27 21:29:21|  分类: 九年级阅读 |  标签: |举报 |字号 订阅

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       近期接连发生的两起天文事件使天外飞“险”成为关注焦点。

       The explosion of a meteor overRussia and an asteroid makinga close encounter with Earth have led scientists to call for more attention to the dangers existing in outer space.
  The meteor exploded early February 15 over Russia’s Chelyabinsk(车里雅宾斯克) region,shattering thousands of windows and injuring 1,200 people.The meteor struck 16 hours before the asteroid,known as 2012 DA14, passed harmlessly within 17,150 miles of Earth. That was the closest pass in a century of a space rock that size.
  “After today, a lot of people will be paying attention,” said Rusty Schweickart, a former NASA astronaut. He helped establish the planet-protecting B612 Foundation and has been warning NASA for years to put more muscle and money into a heightened asteroid alert system.
  Earth is constantly threatened by meteors. But many,if not most of them,are simply too small to detect from afar with the tools now available to astronomers.
  The meteor that exploded over Russia was estimated to be20 times more powerful than the atomic bomb dropped on Hiroshima(广岛)during World War II.And yet no one saw it coming; it was about the size of a bus.As for DA14, astronomers did not even discover it until a year ago. That would have been too late for pre-emptive(先发制人的) action, if it had been on a collision course with Earth.
  Scientists believe there are anywhere from500,000to one million “near-Earth”asteroids comparable in size to DA14 or bigger out there.But less than one percent have actually been spotted.
  A 100- to 130-foot asteroid exploded over Siberia(西伯利亚) in 1908 and flattened 825 square miles of forest, while the rock that is believed to have wiped out the dinosaurs 65 million years ago was a monster 6 miles across.
  All this points up the need for more money for tracking of near-Earth objects, according to Schweickart.
  NASA scientist Bill Cooke said the space agency takes asteroid threats seriously and has poured money into looking for ways to better spot them. Annual spending on asteroid-detection at the space agency has gone from$4million a few years ago to $20 million now.

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