Ganymede

Ganymede is the largest moon of Jupiter and the largest moon in the Solar System, with a diameter of 5,268 km (3,273 miles). It is the only moon known to have a magnetic field, and it is larger than the planet Mercury, though it is only about half as massive. Named after the mythological cupbearer of the Greek gods, Ganymede (גניימדה in Hebrew, 甘尼米德 in Chinese, and Ganymède in French) is one of the four Galilean moons discovered by Galileo Galilei in 1610. It is composed primarily of silicate rock and water ice, and it has a surface that is a mix of two types of terrain: bright regions with ridges and grooves and darker, older areas with more impact craters. Ganymede is also the only moon known to have a substantial atmosphere, composed mostly of oxygen. Its magnetic field suggests that it may have a liquid iron core, and it is believed to have a subsurface ocean of saltwater, making it a target of interest in the search for extraterrestrial life.