Well I can't give the link directly to it: its on deviantart.. and my school has blocked that :)
so goto torrobinson.deviantart.co m and goto the most recent thing in my "gallery"
The BIG planet was composed mainly of a some grunge brushes (the texture) and bits and pieces from some textures of Mars, Venus, and some mud ( :) )
The small planet is pretty featureless because I think I used like 2 brushes... or something.
And the thing below them (I don't know what it is... a nebula?) is using a technique with clouds.... obviously.. so.. yeah