Nicely done, although one aspect of the image screams "help" at me.
That would be the lighting. In any system, the local sun is the main source of light (in most cases). Thusly, all lit regions of planets, asteroids, whatever celestial bodies point towards it. You've made a fundamental compositional error by aiming the planet lighting in opposite direction. The light sides of the planet should face the sun, unless there's more light sources of a similar strength to take into account.
If you could fix up that, then it's all gravy. Otherwise, it's just nice. Planets are well textured although slightly pixelly, starfield is alright, I can't say the ship appeals too much, or adds compositionally, though. The cloud transition is a little weird too, it suggests that you can see through the clouds (best to have low cloud cover). Terrain I think could do with some work, also the surface map, a little too simplistic and again, pixelly.
This IS great...first I love that BLUE nad your way to make the lay out...hmm...I´m a photographer, so this interest is because of THIS IS INTEREST. Great - and have a nice weekend. BTW for a long time my first FAV on this category