It's not only shrinking it also gets higher.
And Jupiters (and again my memory play tricks with me) Jupiter and some of its moons have the same we have here on earth. A things which makes it possible to watch polarlight
The satellite Juno's investing of Jupiter have shown disturbance of this electric magnetic thing.
https://www.skyatnightmagazine.com/s...vered-jupiter/
Markus