Hey i was wondering how you also did your planets. I am so thankful for your help on the ships thanks again for that. here are some i have made http://imgur.com/a/Rkljx
The planet sprites are done by making a 3D planet in Blender, then adding at atmosphere in Gimp using the planet shape in Blender. It's a lot more complicated process than the 2D ships. The smaller planet sprites are just spheres with procedural textures.Glad I could help you with making ships, looks like you've came up with your own style, nice.
I like a lot your works, its amazing!! congrats!