title: Ganymede (moon)
text: Ganymede[p]  is the largest of over 66 moons of the planet Jupiter. It is also the largest moon in the Solar System. Ganymede is larger in diameter than the planet Mercury, but has only about half of its mass. Ganymede is much less dense. Ganymede is part of a group called the Galilean Satellites. These also include Io, Europa and Callisto.
  
  Galileo Galilei discovered this moon in 1610. Simon Marius suggested the name "Ganymede" soon after. In Greek mythology, Ganymede was Zeus' cup-bearer. This name and the names of the other Galilean satellites were not favoured for a long time, and were not put into common use until the mid-20th century. Instead, it is simply referred to by its Roman numeral designation (a system that was introduced by Galileo) as  or as the "third satellite of Jupiter".  Ganymede is the only Galilean moon of Jupiter named after a male figure.
  
  Structure 
  Ganymede is composed of roughly equal amounts of silicate rock and water ice. Its body has an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth's oceans together. Its surface has dark regions, with impact craters dated to four billion years ago. This covers about a third of the satellite. Lighter regions, crosscut by grooves and ridges and only slightly less ancient, cover the rest. The cause of the light terrain's disrupted geology is not fully known, but was likely the result of tectonic activity caused by tidal heating.
  
  Notes 
  [p] ^ The name "Ganymede" is said as /Gan-ee-Meed/.
  
  References
  
  Other websites 
  Ganymede 
  
  Jupiter's moons