Jupiter has four large moons – Io, Europa, Ganymede and Callisto – with diameters of more than 3000 kilometres. However, as of April 2023, we know it is also home to 91 additional small satellites.

More pocked with craters than any other object in our solar system, Jupiter's outermost and second-biggest Galilean moon, Callisto, appears geologically unremarkable. In the 1990s, however ...