Jupiter is the largest planet in the solar system, with a diameter of 85,788 miles. It is named after the Roman king of gods and has a colorful appearance with white, orange, brown, yellow and red clouds made of poisonous gases like hydrogen and helium. Jupiter has over 60 moons, including the four largest - Europa, Callisto, Io, and Ganymede. Spacecraft that have flown by Jupiter include Pioneer 10, Voyager 1 and 2, Ulysses, and Galileo.