That is a really nice image with really good detail. I would for a start in GIMP select and feather around the planet then invert the selection. Then i would make adjustments to levels to get rid of the blue around. Contrast could do it.
I would then as much as possible use Registax and wavelets to attempt getting more detail. Possibly enlarge the image with Interpolation although I am experimenting with another feature in Registax for enlarging.
I wouldn't change the planet colouring as it usually doesn't provide a good match at the end. The colour you already have is very good, the blue tinge I believe could be viewing conditions that registax seems to leave behind, but it could also be camera white balance too.
What the hell I am still learning as well
. Brilliant job.
