very nice!
And here is the tutorial. 
Impressive job on Europa!
Thanks for the tutorial.
I would consider diffuse roughness ~1 (oren nayar, although I haven’t seen much reference photos, but I certainly would for our moon), use the point light to simulate reflected light from Jupiter, and rather have a tiny sun lamp for the actual sun. Also, I’m not sure I would do stars that way since a shallower field of view would render the stars as blobs rather than continue to be points. If blobs are desired, the size should be kept constant (not sure how to do that). In extreme closeups the UV sphere would probably also cause pinching at the poles, so I don’t see a point in using UV sphere when spherical texture projection is being used anyway - why not go with a round sphere?
Heh. I have done the same thing:
I do not have a lot of knowledge about these specifications in making CG planets. If you can write exactly what I should change, I can make a better tutorial for my next planet.
Ignore oren nayar for now, I’ve been experimenting lately and I can’t get good results with tiny crescents (backlit). Disney shader O-N combined with sheen does it way better (imho). O-N basically means a flatter shading model that doesn’t go much darker towards the rim; when looking at a full moon, it’s hard to tell if it’s a 3D sphere or a 2D disk (if you didn’t know what shape it had). Round cube can be found under add mesh if you enable the addon. Easier to shade and probably to paint on, but a proper UV sphere or proper nurbs sphere would have been preferred. O-N is enabled by cranking up the roughness value of the diffuse shader (works for face on, not so much for crescents, compared to the real deal anyway, imo :)).
