The stars and space look amazing, only thing i see that could be improved are the big really bright white spots. Kinda kills it imo.
Now the planet. There's one thing I see in almost EVERY planet photoshop work, and it's the crappy outer glow. Idk for you guys, but it looks really lame to me :\. It pretty much kills the entire thing. Here's the first and only planet I ever made.
http://ph0xy.deviantart.com/art/Green-I ... e-89389478
The outer glow is still kinda too bright, but better than a normal glow. Also, maybe add a little contrast to the planet, and make it less of a perfect circle.
Still, overall is really good. The stars really blew my mind ;D