"They ran into each other. Nothing has the right of way
up there. We don't have an air traffic controller in space. There
is no universal way of knowing what's coming in your
direction."
Source: Nicholas Johnson, the chief scientist
for orbital debris at NASA's Johnson Space Center in Houston. On
Tuesday, a defunct Russian military satellite collided with an
active Iridium communication satellite in orbit, about 490 miles
above northern Siberia... in what is believed to be the first
documented case of an accidental satellite collision.