The largest moon in the Solar System is bigger than Mercury and hides an ocean beneath its icy surface

Ganymede, Jupiter's largest moon, is larger than Mercury and is the largest moon in the Solar System.

Ganymede is believed to harbor a subsurface saltwater ocean beneath an icy crust about 150 kilometers thick, potentially containing more water than all of Earth's oceans.

Ganymede is the only moon known to generate its own magnetic field.

Ganymede has a layered interior with an iron core and rocky mantle, making it planet-like.

Ganymede was discovered by Galileo Galilei in 1610; observations from the Hubble Space Telescope indicate the presence of its hidden ocean.