Scientists say there may be an ocean lurking below on the biggest moon in the solar system.
The Jupiter moon Ganymede is one of a growing number of moons that are thought to have water underground.
Ganymede's ocean is believed to be much deeper than oceans on Earth - about 96 kilometres thick and sandwiched between an icy crust and rocky mantle.
The latest evidence comes from the Hubble Space Telescope, which observed the moon's magnetic field to get a glimpse of its interior.
Scientists have long suspected there was an ocean beneath Ganymede and they say Hubble provides the most convincing evidence yet.
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The European Space Agency wants to launch a mission in 2022 to explore Jupiter and three of its moons including Ganymede.
