Jupiter's moon Ganymede is the largest planetary satellite in the solar system. It's also one of the most intriguing: Ganymede is the only moon with its own magnetic field, it is the most differentiated of all moons, and it likely possesses a subsurface ocean of liquid water. It was studied by the early Jupiter flybys made by the Pioneer and Voyager spacecraft, but our understanding today rests largely on observations made by NASA's Galileo orbiter from 1995 to 2003.
source https://phys.org/news/2021-01-juno-ice-northern-ganymede.html
