Voyager 1 took the first photo of Jupiter and its largest moon Ganymede from over 25 million miles away, showing the Great Red Spot. Jupiter has the largest planets in the solar system, along with at least 63 moons including the Galilean moons - Io, Europa, Ganymede and Callisto. Jupiter is mostly hydrogen and helium gas and has a massive Great Red Spot storm that is over 300 years old.