Ganymede (moon) has an ionosphere associated with its atmosphere is unresolved. Ganymede's discovery is credited to Galileo Galilei, who was the first to observe it on January 7, 1610. The satellite's name was soon suggested by astronomer Simon Marius, after the mythological Ganymede, cupbearer of the Greek gods, kidnapped by Zeus for the purpose. Beginning with "Pioneer 10", several spacecraft have explored Ganymede. The Voyager probes, "Voyager 1" and "Voyager 2", refined measurements of its size, while "Galileo" discovered its underground ocean and magnetic field. The next planned mission to the Jovian system is the European Space Agency's Jupiter Icy Moon Explorer
Stability of the Solar System that keeps the far side of the Moon away from the Earth. Mercury is in a 3:2 spin–orbit resonance. The planets' orbits are chaotic over longer timescales, such that the whole Solar System possesses a Lyapunov time in the range of 2–230 million years. In all cases this means that the position of a planet along its orbit ultimately becomes impossible to predict with any certainty (so, for example, the timing of winter and summer become uncertain), but in some cases the orbits themselves may change dramatically. Such chaos manifests most strongly as changes in eccentricity, with some planets' orbits