英语听力：探索发现 科学新发现：我们的大气层-22

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  Meteorites³ will have iron in them, and it's ? So not only  will magneticbe attract to it, but also metal detector will be able to pick it up. Every year, over eighteen thousand meteorites lock onto collision course with the earth.

  When meteorites encounter our atmosphere, they are travelling at the speed that they acquire moving through the vacuum  space. And typically, they are travelling at many thousands of miles per hour. 

  As they head down to earth, they cut through the outer reaches of our atmosphere. But once the meteorite² enter the mesosphere, the air starts pushing back.

   We can't see the air around us. We can only feel it on really windy days like this. But a meteorite encountering our atmosphere definitely feels the air and that is because it's travelling so quickly. When it encounters our atmosphere, the air in front of the meteorite can not get out of the way in time. It's almost like the meteorite hitting a solid wall like a block of concrete.

  As the air in front of the meteorite compresses, it also heats up to more than three thousand degrees Fahrenheit⁴. Eventually it bursts into flame, lighting⁵ up the sky. When you saw a falling meteorite or a shooting star, it's actually the protective shield of air that you see burning, not the meteorite itself.

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