Originally posted by Carl
the planets are not models, they are pictures. they are not being rendered in real time by game's engine. bump mapping wouldn't make any sense, an it would in fact make them look more like disks than spheres, and there is no point to bump maps since they can be made bumpy or smooth to begin with, since they are, after all, pictures.
yeah, as Bob says, this is not true, bump can work on a 2D map ( coz after all, it's a 2D effect applied to a 2D texture, think about it

), and you can kind of simulate a sphere with bump maps.
Tho, after being wrong you're right (

) the effect can be rendered directly on the planet image, so there's little point using that.
Bump is interesting only on moving objects, coz it's processed using lighting data. if the light source around it doesn't move, bump is useless, having the relief directly drawn is better ( that's the case on a background image ).