you could have chosen some higher resolution textures for the planets, you also (next time) might want to smooth out the edges of your planets a little better.
anyways its still pretty nice just needs a few touch ups.
ps. these people below me crying over it being "Photomanipulation" i disagree on the basis of it being completely created from scratch. he has not gotten a previously made photo, placed a filter upon it and then posted it here. he has used photoshop, used an array of tools, effects, and techniques to create this.