Thanks!
I've seen that file before, and it makes no sense to me, especially considering the error messages I get. Like I said, I need something simple, and the node structure is something I can't wrap my head around in that file.
Surely there must be some (relatively) easy way!
I'm thinking of creating a displacement map from scratch if no one can provide a better answer.
@Kadri: I get 31 warning messages from your file. Apart from that, I see no ridges, and can't zoom in properly to see the planet in the background, which I'm assuming is the one with the ridges.