Space may be incomprehensibly vast, but Earth’s environs are crowded with junk. Spent rockets, derelict spacecraft, satellite fragments and loose hardware now form a cloud of debris that poses a threat to orbiting satellites and astronauts. Sky watchers have catalogued more than 16,000 objects larger than about 10 centimeters, most of them in low Earth orbit, at altitudes of 200 to 2,000 kilometers.

And the junk is self-sustaining. If humankind were to cease all spacefaring activities, the hardware we have already cast off would continue to collide and fragment into bits for centuries. Maintaining current launch rates would make the problem even worse. The number of space objects has shot up in the past five years because of China’s 2007 test of an antisatellite weapon and the 2009 crash between Russian and U.S. satellites. Governments are contemplating cleanup measures but have yet to devise a workable solution.

Credit: Jan Willem Tulp, Sources: Ting Wang Stanford University (2012 debris data); J.C. Liou NASA Orbital Debris Program Office (future projections)