Some Solar System moons are quite well know, others are less so. Nonetheless, the orbits of these moons can help us determine the masses of their planets. One of Saturn's moons, Pandora, has an orbital period of 0.629 days and a semi-major axis of 141,700 kilometers. One of Uranus' moons, Belinda, has a very similar orbital period of 0.624 days, but its semi-major axis is only 75,260 kilometers. Based on this data, which planet must be more massive? How does the data make this clear?