I'm no expert in planetary imaging but I think the ring around the limb is probably due to 2 effects: planet rotation; and or alignment of frames.
The planet rotates ~ 10hrs, very fast for such a large planet, thus the data between the 1st and last frame differ and the processing cannot compensate for this. The only way to negate this effect is to take smaller number.
Successive frame alignment is difficult as the image dances around with currents in the ota and atmosphere. You can tell good nights and a cool ota as the image sits nice and steady in the sensor. Indeed there is a lot of planetary imagers who seeek good locations, like on a small'ish island to obtain best atmospherics.
Your image is real good though don't get me wrong it's a credit and well done.
pretty much Mike covers all these (and more) bases in
his how to article.