But there are also other hazards from space. Thousands of nuts, bolts ,and other debris from space missions form an orbiting garbage dump. Some of these bits and pieces fall back into Earth's atmosphere and behave just like any other meteor ,lighting up the sky like "falling star". According to nasa ,there must be over 100,000 objects with a diameter of one to ten centimeters floating around space. The number of fragment less than one centimeter could be in the millions. The u.s. space Command is aware of the threat of an orbital impact during space missions and monitors this junk constantly . The agency estimates that there might be more than 3,000 satellites orbiting Eart . In February 2008,for example ,the United States blew up a satellite that contained toxic fiel. It was exploded over the pacific ocean so that it could not fall and harm humans. some scientists speculate that one day there might be orbiting "garbage collector" machines to pick up the debris.