Observable Objects in Orbit - 1989

Source for the following: European Space Agency

ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany, tracks space litter. It estimates that over 23,000 objects larger than 10 centimetres have been launched from Earth. Of these, about 7500 are still orbiting - only a very small proportion of them (6%) is operational. Half of all the objects are inoperable satellites, spent rocket stages, or other large space litter; the remaining 44% is debris from explosions and accidents in space. To make things worse, there are an estimated 70,000 to 120,000 fragments smaller than 1 centimetre and the amount of space debris increases by about 5% every year. Tiny fragments, such as paint flecks, moving at very high velocities of around 6 kilometres per second can create problems for the spacecraft and for astronaut. One way to lower the threat is to remove satellites from orbit at the end of their working lives. If we force satellites down through the Earth's atmosphere, they burn up. However, this is more complicated if the satellite is so large that parts of it are liable to survive reentry and strike the ground. This is the case for some Earth observation satellites, for example, which are very big and heavy. When removing a (dead) satellite from orbit is too difficult, it is simply left in orbit. - Publication Date: 26 September 2002

According to an article at SPACE.com solar activity can influence how much orbital debris reenters the atmosphere and burns up. "There was a clear decrease in the population [of orbital debris] around 1990 during a period of high solar activity. 'Unfortunately, the last solar max did not produce a similar result,' [Nicholas Johnson, Program Manager and Chief Scientist of the NASA Orbital Debris Program Office] said."

The following plot contains more recent information on orbital debris categorized by object type.