Oh sorry, I'm messed up here with the light thing.  I see you are using a distant light (good choice).  It won't matter where you move that light, what will matter is how it's pointed.  So here's my suggestion for that.

Add a behavior to the distant light to point at the planet.  Then when you move it, it will change the direction that it's pointed and then it will do what I have implied in the previous post which is to change the direction the light is coming from.

If you don't know, distant lights work as thought they're at infinity and shine in the direction they are pointed.  Their position in the scene is irrelevant given that they operate as thought they are from infinity.  So that might be part of the issue about how your lighting is or isn't working.  It also means that if you want the soft shadows to truly work, you need to set the size of the light source big.

Sorry about leaving out that tidbit.  Let me know if that helps.

-Kix