One of the first New images of Ganymede from the June 7, 2021 Juno flyby.
Image Cedit: NASA/JPL-Caltech/SwRI/MSSS.

Jupiter’s largest moon is Ganymede. It was discovered in 1610 by Galileo. Ganymede is larger than the planet Mercury and it is the only moon that has a magnetic field like the Earth’s. It is also one of the moons thought to have a subsurface ocean that is estimated to be about 60 miles thick.