A friend of mine (who is a friend of yours I think) linked me to this as I'm into Mucha art, and well.. I live in Japan and like all sorts of things here but recently had a mini Sailor Moon obsession. This is really beautiful and kind of inspiring! 8D
(You asked for critique, so) Can I ask how you did this? It looks like each of the girls faces are made from the same basic shape. I'm not criticizing that, though! I like the way the texture makes it look antique.
I would suggest putting something in the background circle of each girl. Something showing what their planets are like a symbol of their planet in the corner, or the elements they use in the background. Like for example perhaps a big wave and/or bubbles behind Mercury, and like snow or something behind Moon, leaves or a tree branch behind Jupiter, flames behind Mars, and stars or sun beams behind Venus or something like that. not taking up the whole dial but just like placed in some kind of artistically balanced way.