Ganymede

Ganymede, Jupiter's largest moon, is the largest object in the Solar System without a substantial atmosphere. It has a substantial magnetic field, likely generated by convection within its core, and orbits Jupiter in roughly seven days. The moon is composed of silicate rock and water, with a fully differentiated body and an iron-rich core. Ganymede's surface features two main types of terrain, lighter regions with extensive grooves and ridges, and darker regions with impact craters. Its discovery is credited to Simon Marius and Galileo Galilei in 1610, who also suggested the name Ganymede after the mythological Trojan prince. Several spacecraft have explored Ganymede, including Pioneer 10, Voyager 1 and 2, and Galileo, which discovered its underground ocean and magnetic field. The European Space Agency's Jupiter Icy Moons Explorer (JUICE) is planned to enter orbit around Ganymede in the future.learn more on wikipedia