There is lots of junk （垃圾） in space. Some of it is from rockets. In 1996, a rocket broke into about 300,000 small pieces. So far, scientists have found over 10,000 man —made pieces flying around in space. Only 6%~7% of them are satellites and space probes （探测器）. Astronauts also lose small things while working in space. In 1965, during the first American spacewalk, astronaut Edward White lost a glove. For a month, the glove stayed in space, travelling at a speed of 28,000 kilometers per hour. It became the most dangerous piece of clothing for the earth in history it flew away.
Things move very fast in space. If they hit （碰撞） one another, it can be dangerous. A little piece of paint from a satellite once made a hole in a spacecraft window. Last year two US spacecrafts dropped some bolts （螺栓）, and scientists on the earth worried a lot. Luckily the bolts floated （漂浮） away into space. They could not hit the spacecraft.
