There's a strange little cap on the pole of the moon... something gone wrong there?
Yeah, didn't notice that before I posted it. Must have happened in post. Been back and re-rendered that area and it's not there. I did some masking for the lens flare/blur and must have introduced it there.
Been back and composited the test render with the original and dealt with it.
The starfield is one from here http://forums.planetside.co.uk/index.php?topic=4391.msg46100
I did do a bit more trickery though...
I rendered another complete copy of the background without any planets or objects and left out the space dust in the background clip. This gives an exact duplicate of the stars that can be adjusted in levels, etc in Photoshop and composited over the render. In this way you can do subtle tinting and flaring on a star by star basis by simply painting over the star on it's own layer.
It makes the stars really pop, I think.