Ganymede’s hidden ocean

Quick facts

• Discovered by Galileo Galilei in 1610, one of Jupiter’s four large “Galilean” moons.
• About 5,268 km across, the biggest moon in the solar system.
• The only moon known to have its own magnetic field.
• Evidence for an underground ocean came from the Hubble Space Telescope in 2015: Ganymede’s aurorae rock less than expected, which is best explained by a salty, electrically conducting ocean beneath the ice.
• Estimates put the ocean roughly 100 km deep under a shell of ice perhaps 150 km thick, which could mean more water than all of Earth’s oceans combined.

Missions on the way

ESA’s JUICE (JUpiter ICy moons Explorer) launched in 2023 and is due to reach Jupiter in the early 2030s, then orbit Ganymede itself, the first spacecraft to orbit a moon other than our own. NASA’s Europa Clipper, launched in 2024, studies Ganymede’s neighbour Europa, another icy moon with an ocean.

Could anything live there?

Nobody knows. Life as we know it needs liquid water, energy and the right chemistry. Ganymede has the water, but its ocean may be sandwiched between layers of ice, which could limit the chemistry from the rocky floor. It remains one of the places scientists most want to explore.

The game’s alien ocean

In Fish of Ganymede the ocean is dark, deep and full of life that makes its own light. Its fish borrow ideas from Earth’s own deep sea (see the real deep-sea fish behind them) and their bodies are grown from genomes you can breed. You can dive in right now, free.