So now we know what really happened... A rat with a net full of asteroids.
@ Max: I was hesitant to post more WIPs as I did this over quite a brief period of time and didn't want to spam the forum. Because I had to work quickly a lot of the time there was no 'buildup' to speak of; I went from raw sketch to almost complete mountains in one go, for example. If you'd like I could post a layer-by-layer view? Here's the original sketch I started off with.