A common misconception of space is illustrated by the Star Wars movie: an explosion occurs and the screen is filled with debris, but a moment later it clears. The debris is gone without a trace. In fact, debris and charged particles injected into near-Earth space are trapped by Earth's gravity and by the geomagnetic field, and they become hazards to spacecraft until they are removed by interaction with Earth's upper atmosphere.

Eventually debris particles will collide with enough air molecules to slow them down, go into decaying orbits, and reenter the atmosphere. When the sun flares up in its eleven year cycle, it heats the upper atmosphere and makes it expand so that debris and spacecraft in lower orbits are subjected to increased drag. But the higher the original orbit, the less air there is to collide with. Above about 800 km, the atmosphere is so thin that the lifetime of orbital debris may be many decades. Above 1000km, debris may orbit for centuries.

Imagine near-Earth space as the hillsides of a steep valley. A lake lies at the bottom, washing debris off only the lowest part of the hillsides regularly. The lake is our atmosphere. Not only is near-Earth space filling with debris, the atmosphere itself is polluted with stratospheric chlorine from every launch using solid rocket fuel, which also dumps tons of particles into the atmosphere and near-Earth space.

Space is the most fragile environment that exists because it has the least ability to repair itself.