Artist's concept of the Earth, Pluto, Charon, and Earth's moon to scale. - stock illustration

Artist's concept of the Earth, Pluto, Charon, and Earth's moon to scale (from left to right). Pluto has a diameter that is less than a fifth of the Earth's and is smaller than Earth's moon. Pluto's moon Charon is over half the size of Pluto itself, leading astronomers to originally classify the Pluto09/14/2009Charon system as a double planet. They are also considered binary planets because the smaller Charon doesn't actually orbit around Pluto, rather Pluto and Charon orbit a common gravitational center (the barycenter) located above Pluto's surface.