* Ganymede is the largest moon in our solar system. Its larger mass means it has a stronger gravitational pull than Callisto.

* Ganymede is closer to Jupiter than Callisto. Gravity decreases with distance, so the closer an object is to Jupiter, the stronger the gravitational force between them.

While both Ganymede and Callisto are large moons, Ganymede's combination of greater mass and closer proximity to Jupiter results in a stronger gravitational force between it and the planet.