The following information was kindly contributed by Russell Odell. Pluto is the black sheep of the solar system. Astronomers ignore it. It is the only planet in the solar system that lacked the importance of being visited by a space probe. Charon is about half the size of the planet.
Moons are always much smaller than the planet they orbit.
As an example, our moon is about one fourth the size of our earth. The moons of Jupiter, Saturn and Neptune are much smaller than their respective planets. Some speak of Pluto and Charon as odd ball satellites of Neptune that somehow, broke loose from Neptune's gravitational domain. It took many years of intense research to find Pluto. It began in earnest when the astronomer Percival Lowell who built, at his own expense, an observatory, because he was obsessed he could find life on the planet Mars.