Either go for a complete cartoony look or a realistic one. You've kind of gone inbetween, your planet looks real ( well it doesn't.. but .... ya get me ) . Work on the texture for that, it's too blurry, the planet's too big, and the colour has nothing to do with the lightsource. DON'T post art if you know what's wrong with it already, change it. THen post it. That's just stupid :P
I'd try a cartoony one.. or spend around a week working on a Decent peice