Physics Issues?

Im trying to figure out how to set up physics on a planetary basis, ie I have the First Person Controller the world/terrain is a Sphere when the FPC moves around the Sphere how do I stop it from falling off.

Ideally I would like the Sphere to have some sort of real world gravitational/mass thing going on as there will be a number of them within the scene which I would like the FPC to move about on and between.

Go easy please I have a Maya background not a gaming /scripting one

Cheers