Kelly Young in New Scientist:
In January 2005, the US Space Surveillance Network saw a 31-year-old US Thor rocket body collide in space with part of the third stage of the Chinese CZ-4 rocket that exploded in March 2000. At least three pieces broke off the Thor rocket stage, adding to the growing collection of space junk orbiting Earth.
Now, NASA researchers have calculated that such occurrences will only increase. Even without launching any additional spacecraft, the number of new fragments created by collisions will exceed the number falling back to Earth and burning up by 2055.
And reaching that tipping point by 2055 is a best case scenario…
This is of concern to space-faring countries because even a centimetre-sized speck of debris, speeding along at thousands of kilometres per hour, could damage an operational satellite.