> Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in space – principally in Earth orbit – which no longer serve a useful function. These include derelict spacecraft (nonfunctional spacecraft and abandoned launch vehicle stages), mission-related debris, and particularly-numerous in-Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft.
> The higher the altitude, the longer the orbital debris will typically remain in Earth orbit. Debris left in orbits below 600 km normally fall back to Earth within several years. At altitudes of 800 km, the time for orbital decay is often measured in centuries. Above 1,000 km, orbital debris will normally continue circling the Earth for a thousand years or more.
Struck by other smaller but high energy debris, faulty batteries that are still receiving charge from unshunted solar arrays, similar mechanical failures from attitude control systems, unused propellant leaks or ruptures. There are a lot of things that can go wrong which is why we have the 25 year rule now.
Or another angle -- what percentage of satellite EOL events is "breaking up into a debris field" (vs "burning up in the atmosphere")?