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SPACE JUNK
The twinkling stars on a clear night may took free of human pollution, but according to NASA, there are over half a million pieces of space junk orbiting our planet. This is 1) ........................ up of manmade rubbish from past space missions. It circles the Earth at speeds of 2) ............ to 17,500 mph and poses a real threat to satellites, spacecraft and space stations. NASA estimates that there are more than 20,000 items bigger 3) .................. a tennis ball flying around. Sometimes pieces of space junk fall to Earth. Don't worry too much, though, as the probability of 4) ............ hitting is extremely small.