How to add a semi cloudy volumetric atmosphere

[xxdanbrowne]

So I'm playing around with a space scene I made (Stargate fan scene)... I got the color map of the planet and the cloud map down. I think it looks pretty good. Only thing is the atmosphere mesh on top of which is layered the cloud map isn't volumetric. So you can see the clouds wrap round the planet. I wonder how to make the atmosphere mesh layer look like it has some depth to it?

[xxdanbrowne]

Maybe looking at it from the wrong angle:
falloff node!