The two largest planets in our solar system, Jupiter and Saturn, also have the largest satellite systems, or the most moons. At present, Jupiter's reported moon count stands at more than 100 moons, and along with its many rings, Saturn has more than 280 reported moons. Not all these moons are equal, however. Jupiter's moon family has four large members, including the largest moon in the solar system, Ganymede, while Saturn's family is dominated by one large moon, Titan, the solar system's second largest.

Specifically, Jupiter’s strong magnetic field caused the formation of a magnetospheric cavity in the circumplanetary disk around the young gas giant, which likely captured the moons Io, Europa, and Ganymede. In contrast, the young Saturn’s magnetic field was too weak to form a cavity, so the migrating moons cannot survive in the disk.