Planet Color Studies

I'm continuing to work on optimal control for rockets. Practical Methods for Optimal Control and Estimation Using Nonlinear Programming looks like a very good book on the subject. I just got a copy, but I found a PDF of it online somewhere that convinced me it was worthwhile.

In the meantime here are a couple of color studies for 2D planets:





Which of the following two options would be better?

• Always show planet in cross-section
• Have a foreground layer that fades away when the player is underground

A foreground cap could add to the exploration aspect of the game by hiding underground tunnels. On the other hand I'd have to draw a spherical planet on it or something, which would be tricky to do well.