Charon
Charon is a moon of Pluto, and it’s little compared to other solar system moons, but large compared to its parent body, which was once considered the smallest planet in the solar system. Together, the two bodies form the only known double planetary system, in which the same sides of Pluto and Charon always face one another. (For comparison, an observer on Earth always sees one side of the Moon, but on the Moon you’d see all sides of Earth as it rotates).
Charon is a relatively recently discovered solar system moon, discovered by a United States Naval Observatory astronomer in 1978.
