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Charon is the largest moon of Pluto and was discovered in 1978, forty-eight years after Pluto was discovered. The satellite was discovered by the astronomer James W. Christy, a scientist at the U.S. Naval Observatory, who noticed a bulge on a photo of Pluto. It turns out that pictures of Charon had been taken for 13 years before it was actually discovered. Until then, it was believed that Pluto was bigger than it is because Charon blended in with Pluto.
Charon is small relative to other celestial bodies. However, at 4.58 x 106 km2, it is only a little bit less than two and a half times the square footage of Alaska, which is by far the largest state in America. So far, scientists have not been able to calculate the satellite’s density or mass accurately. From what they have been able to gather, scientists believe that its density and composition could be similar to that of Rhea, one of Saturn’s moons. On average, Charon and Pluto are 19,570 kilometers apart.
Like many other satellites, Charon received a name that related to its planet’s name. Charon is the name of the ferryman of the dead in Greek mythology. Pluto is the Roman equivalent of the Greek god of the underworld, Hades. As with many other celestial bodies, there is also a dual reason for the name chosen. Charlene is the name of James Christy’s wife, and her nickname is “Char,” which is somewhat close to Charon.
Charon is somewhat of a puzzle when it comes to classification. Throughout this article, it has been referred to as a moon or satellite; however, neither Pluto nor Charon actually orbits the other. Instead, the planets are locked in a synchronous orbit, which means they always have the same side facing each other. Because of this situation, some astronomers say that Charon should not actually be considered Pluto’s satellite. Since the reclassification of Pluto into a dwarf planet, which happened in 2006, they want Charon to be classified as a dual dwarf planet with Pluto. So far though, Charon has not been added to the International Astronomical Union’s (IAU) list of recognized dwarf planets.
Some scientists have suggested that Charon was formed by an asteroid or other celestial body slamming in to Pluto – the same way the Earth’s Moon was created. Another theory is that the objects were separate and collided before beginning to orbit each other.
Do not forget to tune in to Astronomy Cast’s episode on Pluto and the icy Solar System.