8. Create your gradient. You will see how your planet changes. Experiment with different gradients, different colors.
Save your gradient for future.
9. My result is here.
10. Gradient Map is active (!); Ctrl+Click on planet's layer, inverse selection; Delete.
11. Copy your planet and move layer "planet copy" above Gradient map. Move your planet in other part of your pic, just to make it visible.
12. Merge Gradient Map and Planet.
13. Experiment with another Gradient Maps too. Here You can see my 3 planets: 1st is original, 2d and 3d after my work with Gradient Maps. Of course, you can Flip horizontal them.
14. It's time to make our background. Unlock background; set your background/foreground colors dark blue and ... more dark blue ( i used: #02072C and #000211). Filter--->Render--->Clouds. Repeat it around 7 times (Ctrl+F).
15. Place your planets as you need, Transform them (Edit-->Transform--> Free Transform).
More Tutorials: 
