Nice one, mate
Hope you don't mind, but I did a quick repro in Photoshop CS3...just to bring the image up a little and see what's there.
Just a little levels adjustment, some colour channel tweaking, and a little high pass sharpening.
I checked an astro program and can vouch that's a moon shadow at the right limb... which I think is Europa's shadow.
You've also captured Ganymede in your image.
And of course, the Great Red Spot.
Well done!