Surface of Io. Coloured infrared image of the Tvashtar Catena volcanic region on the surface of Io, one of Jupiter's moons. The image was taken by NASA's Galileo Orbiter spacecraft. It shows molten rock (two small white dots, far left) exposed at the moon's surface, and a cooling lava flow (orange and yellow, below molten rock), both produced by a volcanic eruption. The flow is over 60 kilometres long. Io is the most volcanically- active world in the solar system, with at least 80 active volcanoes. Galileo has recorded temperatures in the Tvashtar Catena region of over 1038 degrees Celsius. The Galileo Orbiter was launched in 1989 to study Jupiter and its moons.