How to make an asteroid (space debris) in Paint.NET
Using Shape 3D and Liquify plugins and some more other effect.
Notice that these are just the basics on how to create the texture and shaping the stone.
You can view also Part1 and 2 for a different texture:
http://www.youtube.com/watch?v=YtVjYhgvioA
http://www.youtube.com/watch?v=1jDCF8pRcik