This picture above is a picture of Ganymede's interior.

  Ganymede is Jupiter's largest moon and was discovered by Simon Marius and Galileo Galilei in the year 1610.  It is the largest moon in our solar system as well as Jupiter's largest moon. It has a diameter 5,262 kilometer's or 3,280 miles.  Like all of Jupiter's moons and satellites Ganymede's surface is mostly   composed of ice.  The core of Ganymede is metallic and takes up half of it's diameter.  Ganymede is named after a Greek god who was a prince whom Jupiter took to be his cupbearer.