Here's how to quickly create a planet.
Make a new document and make sure it is square. Then, set your foreground color to #000000 and your background color to #CDCDCD. Render some clouds:
Now pull up your image variations and move the slider to one slot before fine, then click more blue once, then more cyan twice. You should get this:
Okay, this step is optional, so you can skip this if you want. Add a lens flare near a corner, 105mm prime:
Then use polar coordinates, rectangular to polar:
Now, take out your blur tool and blur along the line from the polar coordinates to remove it. Then grab your elliptical marquee tool and hold down alt+shift. Then click in the center and pull out until you've selected the entire sphere.
Inverse the selection and press delete and deselect. Now add a hue/saturation layer and use these settings:
The add a brightness/contrast layer and use these settings:
Add an outer glow using these settings:
Done! Here's my final product, use it if you want, but you should make your own.
Here's an example of what I made with this tutorial:
God took seven days, well, we took seven minutes!