Nice work! Your barren and ice planets look like they could have been lifted right out of EVE Online, actually.

As I consider these a bit more, the highlights look strange to me. It looks a bit like the planets are made out of plastic. I don't think a planet's atmosphere should probably have a specular component. Maybe if you set your highlight to overlay it would simply brighten up what's underneath instead of diffusing.

Also, the edges of your fire planet's thermosphere got cropped on the edges. It looks particularly strange on the left side, where you apparently rotated something after the crop occurred.