These are the same planet sprites I allready uploaded (http://opengameart.org/content/15-planet-sprites, http://opengameart.org/content/16-planet-sprites, http://opengameart.org/content/17-planet-sprites), but without shadows and atmosphere. Some normal textures are included as well. I haven't found the source files for few of the graphics and I left out few other of them as they look bad IMO.

You should either add shadows using a new layer or use shaders with 2D lighting to add shadows and atmosphere (what I have done), I haven't made specular maps though.