[Suicide Junkie]

"Effects added to the planet" is stormcloud like things as I understand it. You'd have to make them small and numerous in order to have them wrap around and follow the surface of the planet.
You don't want to use a large sprite, since they always face the camera, and that would look quite wrong when the effect reaches the edge of the model (part sticking into the planet, part sticking out into space, instead of lying on the surface.

As a completely separate idea, planets could be made as a single sprite with a very long and complex animation sequence.