DIX Planetary Science Seminar

Ganymede is the only known moon with an active dynamo today. For decades, many studies interpreted Ganymede's dynamo as arising from convection in a metal core that formed billions of years ago. However, Ganymede likely accreted too cold to form with a metal core, which confounds interpretations of Ganymede's magnetic field as a constraint on the moon's broader history. Here we re-evaluate the thermal evolution of Ganymede's rock-metal interior from a cold start. Our models suggest that metallic core formation at Ganymede may be ongoing—a process not yet observed elsewhere. If Ganymede has an Fe-FeS core with sub-eutectic composition, then gradual mantle warming may expel dense Fe melt onto the growing protocore and stir liquid metal, sustaining dynamo action for billions of years. Brief comparisons will be made regarding Callisto, Europa, and our Moon.