The planet in the background looks fantastic; very smooth. As mentioned, though, the foreground is comparatively messy. The shading on the lower right corner of the space station seems pretty lazy, and a lot of it could benefit from AA, as mentioned.
That background is very smooth, good job! It looks like a painting. -nodnod-
The foreground could use some cleaning on the outer edge, especially near the lower right corner. The blue glassy curved bit is a little jagged, and could use some AA. The center/bottom moon and the ship could also benefit from this.
I think it is really well done, but with just a few more minor tweaks it could be even better.
really neat! reminds me a little of the first scene in space quest II 
Thats just fantastic, Great work my friend.