I would do the craters by making donut-shaped fondant rings and sticking them on the cake before you cover it with fondant. Then just press the fondant into the hollow centers of the donut shapes to make the crater effect.
For the brown, you could replace part of the powdered sugar with cocoa powder as long as you don't mind it being chocolate flavor. Otherwise, lots of brown gel color
Here's an example of the wilton silver dust over gray fondant: http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1363036
If you paint it on with vodka, it's not as glittery as if you brush it on dry. For that cake I did both, painted it and then after it had dried, brushed more dust over it for sparkle.