Jupiter pulls so hard on Io that the moon’s solid ground rises and falls by as much as 100 metres every orbit — a tide in rock the height of a 30-storey building, and the repeated flexing powers the most volcanically active world in the Solar System

Jupiter pulls so hard on Io that the moon’s solid ground rises and falls by as much as 100 metres every orbit — a tide in rock the height of a 30-storey building, and the repeated flexing powers the most volcanically active world in the Solar System

Io looks like a solid moon, but it never holds a completely fixed shape. During each 42.5-hour trip around Jupiter, the giant planet’s changing tidal force can raise and lower Io’s ground by as much as about 100 metres. That is roughly the height of a 30-storey building. It is a tide in rock, not an ocean, and about 500 times the vertical motion of Earth’s solid-ground tide. An imaginary observer standing on Io would be carried through a slow ri…