Jupiter now has only four large moons, but in the early days of the solar system it may have had 20 or more (Image: JPL / NASA)

THE four giant “Galilean” moons orbiting Jupiter are the last survivors of at least five generations of moons that once circled the gas giant.

“All the other moons – and there could have been 20 or more – were devoured by the planet in the early days of the solar system,” says Robin Canup of the Southwest Research Institute in Boulder, Colorado.

The four Galilean moons have played a key role in the history of …