Why is Io called the ‘pizza moon’?

Io is one of Jupiter’s moons. It is a very colourful moon and this has earned it the name, ‘pizza moon’. It is also rather unusual as it has active volcanoes on it. These pour out liquid sulphur which has a rich yellow-orange colour, making Io very colourful. It was in 1979 that the Voyager I probe discovered Io’s volcanoes when it flew past Jupiter.