Jupiter from Io. Artwork of the gas giant planet Jupiter and its cloud bands, seen from Io through the haze of a volcanic eruption. Io, the third largest of the moons of Jupiter, is one of the closest (422,000 kilometres). The powerful gravity of Jupiter and tidal forces from the other moons, create huge tides on Io, powering its volcanoes. These can eject sulphur over 100 kilometres into space. There are hundreds of active volcanoes on Io, making it the most geologically active body in the solar system. Jupiter, the largest planet in the solar system, has an equatorial diameter of 142,984 kilometres. Three of the four Galilean moons (Io is the fourth) are shown here, two at upper right and one at lower left.