Io is the most volcanic world in the Solar System and scientists think they now have a better idea of why that is.
The moon of Jupiter erupts about 100 times more lava on to its surface each year than does Earth.
A re-assessment of data from Nasa's Galileo probe suggests all this activity is being fed from a giant magma ocean under Io's crust.
Researchers tell Science magazine that this blisteringly hot reservoir is probably some 50km (30 miles) thick.
Full Story from the BBC