Ganymede is the largest moon of Jupiter and in the Solar System, and the only moon with its own magnetic field. Ganymede is composed of equal parts rock and ice and is larger than Mercury but smaller than Saturn’s moon Titan. It has a diameter of 5262 km, making it just slightly smaller than Mercury. Its surface gravity is 1/6 that of Earth’s.
Ganymede was discovered in 1610 by Galileo Galilei. It is named after Ganymedes, cupbearer to the gods in Greek mythology.
The composition of Ganymede’s interior is not well known, but it is thought to have a rocky core surrounded by an icy mantle. The surface of Ganymede consists mostly of water ice, with only a small amount of silicate rocks. There are two types of terrain on Ganymede: dark regions (terra) and lighter regions (regio). The dark regions are heavily cratered and are thought to be older than the lighter regions. The lighter regions are smoother and may be younger or have been resurfaced by geological activity.
There are several theories about the formation of Ganymede’s surface features. One theory suggests that the dark regions were formed by impacts from space debris, while the lighter regions were formed by volcanic activity or geysers erupting through cracks in the surface ice. Another theory suggests that all of Ganymede’s surface features were created by impacts from space debris.