Been thinking of doing something like this for a while. The landscape is a composite of 3 renders and the spacescape is entirely photoshop. A picture of a wall of chipped paint and a cloud-map were used to create the planets. Other effects were done by brushing and a bit of photomanipulation.
Software: Vue 5 Infinite / Photoshop CS2
Original Resolution: 1440 x 2160
Used brushes by *midnightstouch
Update: Wallpaper version can be found here: [link]
(no way I could resize it to fit everything, so its only the space part)