Complex sentence: In the outer Solar System the impacts onto Jupiter's moons are sufficient to trigger Ganymede's differentiation but not Callisto's, but the impacts of icy planetesimals onto Saturn's inner moons are excessive, resulting in the vaporization of their ice.
Split into simpler sentences: In the outer Solar System the impacts onto Jupiter's moons are sufficient to trigger Ganymede's differentiation but not Callisto's. The impacts of icy planetesimals onto Saturn's inner moons are excessive, howver, resulting in the vaporization of their ice.