Ganymede is Jupiter’s largest moon and the biggest moon in the entire solar system, even surpassing the planet Mercury in size. With a diameter of approximately 5,260 kilometers, Ganymede is larger than Mercury. It is the only known moon with its own magnetic field, which creates auroras at its poles. Ganymede also has a thin atmosphere containing oxygen, ozone, and hydrogen. Strong evidence suggests a deep subsurface ocean of salt water beneath its icy crust, potentially containing more water than all of Earth’s oceans combined. Its surface features a mix of old, dark, heavily cratered regions and younger, brighter terrain marked by intricate grooves, indicating a complex geological history likely involving tectonic activity. Internally, Ganymede is believed to have a dense metallic core, a silicate mantle, and a thick outer shell of ice and water.