I feel you have a strong piece; its well put together, looks good in high res. My main concern with it though is the sky. Right across the center you have some very noticable banding which just draws my eyes to it. I also am not crazy about the clouds, their level of detail makes them looks a bit simplistic compared to the rest of the subject matter.
While we're on the clouds they also seem to curve quite a bit. Like if you were to flip the image vertically you would have the clouds forming a circle, which just doesn't happen. Lastly (and this is not a big deal) if the light source is the bright white thing in the center, then the light should come across the planet on the left from the side, not over the top.
The strongest point of the image are the explosions coming from the planets. they are a good contrast to the bluish-greenish hue. The planets themselves are very detailed which is always nice to look at. Over all, it looks very good.