.阅读理解

　　(2015·江西两所名校联考)

　　A camera, a glove, a hand tool, even a toothbrush ... they are all up there, above the clouds, going around and around the Earth. There are also thousands of pieces of metal and plastic. Some of them are only about the size of a fingernail. Many are much larger. Scientists consider all these objects to be space_junk,_and they are a problem.

　　Since people first launched rockets into space in the 1950s, we have been leaving behind all sorts of things. Much of the space junk is made up of little pieces of things that were once bigger objects, until they struck each other and broke apart. Sometimes larger pieces survive the extreme heat through the atmosphere and hit the ground or the ocean at great speeds.

　　But space junk falling on housetops is not the biggest worry. Scientists are concerned about the Kessler syndrome. It is named after the American scientist who first thought of the idea in 1978. Imagine what happens when an empty rocket strikes another while orbiting the Earth. Two big things become many smaller things, They then hit other things. The pieces get smaller and smaller until they form a cloud of junk that blocks the path of future space vehicles.

　　Marco Castronuovo, an Italian Space Agency researcher, suggested launching a satellite into space that would get very close to some of the larger pieces of space junk. The satellite would connect a small rocket to the useless object. When the rocket explodes, it pushes the junk into a lower and slower orbit, nearer the Earth. After a time, the junk burns up in the atmosphere.

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