I was speculating that geostationary satellites could be around possibly for billions of years (i.e. much beyond the point where plate tectonics would have erased all traces of human civilization on Earth) and might make interesting artifacts for future aliens to find. But I'm realizing I'm on very shaky ground for all sorts or reasons. I hadn't appreciated that these satellites are in an unstable equilibrium radially. With a slight decrease in radius, atmospheric drag and tidal effects cause radius to reduce further, and vice-versa for an increase in radius - albeit very very slowly. I understand there are various gravitational disturbances (Sun and Moon) that cause the orbits to move a few degrees off off the equatorial plane and also that the Earth is slightly flattened which causes orbits to slowly precess. And finally the Earth is gravitionally lumpy and satellites tend to drift to one of two stable longitudes. I guess my first question is: are these local points of longitudinal stability sufficient to lock the orbital period and overcome the unstable radial equilibrium?