Ganymede (moon) - Wikipedia, the free encyclopedia // &quot;Ganymede (Jupiter III) is the largest moon of Jupiter and in the Solar System, and the only moon known to have a magnetic field...[it has] an internal ocean that may contain more water than all of Earth&#x27;s oceans combined... [Named] for the mythological Ganymede, cupbearer of the Greek gods and Zeus&#x27;s lover.&quot;