seriously nice tho. you make all them planets and moons from scratch? would love to hear about how
I actually composited the background out of free stock images, then unified the palette with gradient maps, color, and overlay layers. I then painted over that to try and unify everything more. I also have a few "stock" planets I've created I use as starting points. I have a couple that I've used forever from way back when Greg Martin first posted his tutorials.
One handy tip I picked up from Kelsey Shannon is that the Smart Blur
filter is a great way to simplify a photography and make it more painterly so that it doesn't appear too photorealistic in comparison.