On his Flickr account, he tells you the exact method of creating these. If you decide to make some Wee Planets of your own, I'd love you to send them to me or post them somewhere I can find them. I would make some of my own, but I just don't think I could pull it off. Who knows, maybe I will one day. And you can bet your bottom dollar I'll make a blog post about it!
Anyways, here are a few of my favorites from his work, which you can see by clicking the links in the first paragraph. What do you think? Are you as jealous as I am?
A special thanks to Chestees for the find.