At 2,200C, the rocks on Io's surface are hotter than any rock has been on the Earth's surface for billions of years.

Jupiter tries to push it away but Io resists. The result is a tremendous build-up of energy in Io's interior.

Close-up on a volcano

It makes Io the most volcanically active world in the solar system.

In many ways Io's volcanoes are unlike those on Earth. They eject a lot of yellow and orange sulphur compounds that give Io what astronomers call a 'pizza-like' appearance.

To reach such high temperatures Io's lava is based on magnesium-rich silicates which melt at a much higher temperature than sulphur compounds.

Scientists have found 12 hotspots on Io, which is about the same size as our moon.

The images were taken by the Galileo spacecraft which has been in orbit around Jupiter since December 1995.