Ok, but why a field of "debris" at 800 Km? I wasn't aware of that many satellites and upper stages in that orbit. Seems like there would be a lot in geostationary or at ~400 Km(or whatever the ISS median is).
Low earth orbit is actually very heavily used. We fly lots of earth observation satellites in polar orbits in that altitude range: earth resources, weather, spy, etc. The Russians also put a lot of stuff there, and because their satellites tended to have short service lives, they replaced them frequently. Besides the usual weather and spy satellites they flew nuclear-powered radars to follow US Navy warships. Radars are subject to the 1/r
4 law so you want them in as low an orbit as possible -- and that means short-lived. But after a few of their reactors came down in places like Canada and Australia, the Russians began to separate the nuclear reactors at end of life so they could be moved to higher "disposal" orbits while the main part of the spacecraft decayed.
Problem is, these reactors were cooled by NaK (sodium-potassium alloy, a liquid metal at room temperature) and it often leaked out. So one important category of debris at certain altitudes and inclinations are these droplets of NaK. It has a very low vapor pressure so they won't evaporate any time soon.
