It looks good.
Although as an obsessive-compulsive realism fanatic I must state few minor qualms:
-The background has too big stars and there are some places where you clearly just have wiped everything out. No biggie. It's still quite good.
-The atmospheric glow on the dark side of the planet is slightly too strong to my tastes. It creates an impression of an impossibly thick atmosphere on the planet.
And, despite the fact that your lens flare is exellently subtle and fits the picture rather well, I would generally not want to see it half as often as it is used.
In situations where you want to emphasize the fact that "this is a picture taken by a camera", lens flares are more than appropriate (if used subtly, like you have). But, in situations when you want to create an impression of actually looking at the object, lens flare == evil. Human eyes don't show lens flares, and I always turn them off in computer games when I'm playing them.
But as I said, this is good looking...
