Ganymede, a satellite of Jupiter, is the largest and most massive of the Solar System's moons. The ninth-largest object of the Solar System, it is the largest without a substantial atmosphere. It has a diameter of 5, km, making it 26% larger. Ganymede, a satellite of Jupiter (Jupiter III), is the largest and most massive of the Solar System's moons. The ninth-largest object (including the Sun) of. Jupiter's moon Ganymede ("GAN uh meed") is the largest moon in our solar system and the only moon with its own magnetic field. The magnetic field causes. The surface of Ganymede, the largest moon in the solar system, is composed of half water ice and half rock. This satellite of Jupiter is unique for its long. Ganymede, largest of Jupiter's satellites and of all the satellites in the solar system. One of the Galilean moons, it was discovered by the Italian. The American space agency's Juno probe has returned some close-in views of Ganymede - one of Jupiter's four Galilean moons and the largest. NASA has detected water vapor for the very first time in the atmosphere of Ganymede — not only Jupiter's largest moon, but the largest moon. Jupiter's moon Ganymede is the largest moon — and the ninth-largest object — in the Solar System. It may hold more water than all of Earth's. Scientists have discovered for the first time traces of water vapor in the atmosphere of Ganymede, Jupiter's largest moon. The US National. With a mean radius of ± kilometers (the equivalent of Earths), Ganymede is the largest moon in the solar system and is even.