Ganymede's hidden ocean exceeds Earth's

Ganymede possesses a vast salty underground ocean whose quantity of water exceeds that of all of Earth's oceans combined. This immense liquid expanse is nestled at extreme depths reaching approximately 800 km down to the rocky floor. The NASA Galileo probe in the 1990s and then the Hubble Space Telescope in March 2015 successively confirmed the presence of this water by studying its influence on the magnetic field and the auroras.