The blues in this are very vibrant and eye-catching. It's what attracted me to this piece.
I like this composition, but a couple things seem a tad off.
That planet has an eclipse thing going on. The glow around the contour of the planet should be equal on both sides of the star. The planet looks like it is lit more from the bottom, but there are no other stars under it to lend to that idea, thus it looks like it's pasted onto a star background.
The asteroids also lack depth. They look like they are all on the same plane, none of them recede into the background, none of them come out further from the others. I suggest trying an atmospheric fog look, which is to lighten the overall color of the object to make it recede. I also agree with the person who suggested to tint them blue. At least give them a blue light source.