Bright Baby Jupiter Could Have Baked Its Moons

A new study suggests that a young Jupiter could have irradiated its four largest moons with light so intense that it vaporized water and stripped them of volatiles. This could explain why the Galilean moons have the compositions they do, from the hellacious volcano-world Io, closest to Jupiter, to ice-crusted Europa, then giant moon Ganymede, to the most distant, the crater-scarred Callisto. The findings offer a plausible explanation for the strange compositional differences between the four Galilean moons, which are thought to have formed from the same cloud of dust circling Jupiter.