Ganymede: a moon the size of a planet with its own magnetic field

Ganymede, Jupiter’s largest moon, is about the same diameter as Mercury but far less massive, thanks to its rock-and-ice composition; it likely harbors more water than Earth’s surface, has a layered interior with an iron-rich core and a conductive ocean, and uniquely generates its own magnetic field, creating a small magnetosphere within Jupiter’s. The moon’s complex geology, thin atmosphere, and tidal interactions mean it is a world in its own right, not just a simple satellite, and the upcoming JUICE mission aims to orbit Ganymede in 2034 to study its ice shell, ocean, and dynamo.