This is no painting. This'd be a painting if everything in this picture was actually painted, that is why you call it a painting. As soon as you use photos (mind that, not as references) it's a manipulation.
Well, this doesn't change that this is awesome, a wrong category doesn't make a bad picture Me likes tbh.
Actually the real moons are barely visible. But I say: WTF. It's a painting not a NASA photo. Very well done. The ground and rocks are the same colour as in the pics taken by Opportunity. The city looks awesome. Yep, a great novel is a good place to find great inspiration.