Nice! All the more reason to figure out how to shield Mars with a magnetic field...
Have you considered the sheer amount of energy in a planetary magnetic field? Currently something like 3x10
16 joules. Which is about 10 megatons per second. Magnetic fields aren't strong, but they are expansive. If we could generate those sorts of energy, it would be easy to remove the Jovian atmosphere & expose the rocky (diamond?) core beneath.
Ganymede probably has the same mechanism producing a magnetic field as Earth - an electrically conductive outer core in circulation over a solid inner core. Except it would be salty water and rock for Ganymede, not liquid iron & solid (super-compressed) iron as with Earth. Decaying radioactive heat is Earth's power source, gravitational squeezing by Jupiter in Ganymede's.
(Counterpoint - Io has a magnetic field also. But it's coupled with and generated by Jupiter's magnetic field directly. Not safe for children, folks!)