Damn, that is really well done dude. Only thing I would suggest is adding some signs of civilization on the night side of the planet: http://spaceflight1.nasa.gov/gallery/images/station/crew-25/hires/iss025e009840.jpg
@Davidperyman: Looks great for a first time sculpt! If you really want to increase your knowledge of anatomy I'd suggest picking up Raphael Gressetti's gumroad tutorial. Imo it's one of the best values for your buck. Latest WIP on my civil war stuffs: