Io

The most volcanic world in the Solar System

Io is Jupiter's yellow-and-red moon that looks like a pizza! It has more than 400 volcanoes, and they erupt all the time. Fountains of lava shoot 300 km high — 30 times higher than Earth's tallest mountain. Jupiter pulls on Io so hard that its insides stay hot all the time.

Io (radius 1,822 km, slightly bigger than the Moon) is the innermost Galilean moon of Jupiter, orbiting every 1.77 days. The pull of Jupiter and of neighbouring moons (Europa, Ganymede) flexes Io's surface by up to 100 m a day — this friction melts its interior (tidal heating). The result: 400+ active volcanoes, sulphur plains (yellow, red and white tones) and eruption plumes up to 500 km high. The volcano Loki gives off more heat than all of Earth's volcanoes combined. Io has no water and almost no craters — its surface is constantly renewed. Jupiter's magnetic field strips a tonne of material from Io every second.

Fun facts

• Io is the driest body in the Solar System — not a single drop of water.
• Io's volcanoes are so big they can be seen through telescopes from Earth.
• Io is one of the 4 moons Galileo discovered in 1610 — proof that Earth is not the centre of the universe.