Discovered 40 years ago today, Charon, the largest of Pluto's five moons, fueled the dwarf planet’s evolution from a telescopic dot into an actual planetary system – and a source of many discoveries yet to come: https://go.nasa.gov/2K0qb9D | NASA - National Aeronautics and Space Administration

Animation of the Pluto-Charon system Pluto and its moon Charon are tidal locked. This means that the two bodies always face each other with the same side. As a result, Pluto "sees" only one side of Charon, and vice versa, Charon always shows Pluto the same side. Unlike most planetary systems, the barycenter of the Pluto-Charon system is located approximately 960 km from the surface of Pluto. This is due to the fact that Charon is relatively large compared to Pluto, its mass is about 12% of Pluto