Kentucky Governor's Cup Practice Test

The key idea here is comparing the sizes of Pluto’s moons. Charon is the largest moon, with a diameter of about 1,200 kilometers, roughly half the size of Pluto itself. Its substantial size also means it carries a large share of the system’s mass, which is why the Pluto–Charon pair is often described as a binary, with the barycenter outside Pluto. The other moons—Nix, Hydra, and Styx—are significantly smaller, so none matches Charon in size. So, Charon is the largest moon of Pluto.