Charon is the largest satellite of the five known satellites of the dwarf planet Pluto; it is more than half Pluto’s size. Even though Pluto was discovered in 1930, Charon was first discovered in 1978 by American astronomer James Christy. Christy first suggested the name, Charon, after his wife Charlene’s nickname, Char, and to the song Sails of Charon by the German rock band Scorpions.
His colleagues suggested “Persephone’’ after the daughter of Zeus and Demeter, who was kidnapped by Pluto and made queen of the underworld. Nevertheless, Christy preferred the name Charon, especially for its reference to the Greek mythological figure Charon, the ferryman of the dead, whose myth is related to the god of the underworld Hades, the earlier name of which was Pluto, which represented the planet of the dead. The name was officially announced by the International Astronomical Union in 1986.
Seeing Pluto and Charon through telescopes is such a spectacular view, it is like two skaters clasping hands. Although they have been together for billions of years, in the same orbit, they are totally different, as the Hubble Space Telescope photographed them in 1994. Pluto is covered with bright and dark features, while Charon is dull grey in color with a darker red patch, which we now know is not due to iron, but to tholins*.
Pluto has a significant atmosphere, which Charon does not have. Exotic ices like frozen nitrogen, methane and carbon monoxide have been found on Pluto’s surface; while Charon’s surface is made of frozen water and ammonia compounds. The interior of Pluto is mostly rock, but Charon contains equal amounts of rock and water ice.
Among the five moons of Pluto, Charon is so big that, with Pluto, the pair is considered a binary planet system. When NASA’s New Horizons space probe made its historical flyby of the system in 2015, it captured a wealth of data about the amazing moon. The moon orbits its planet every 6.4 Earth days, the same amount of time it takes Pluto to rotate once. Both are tidally locked, with one face permanently turned toward the other.
The Pluto–Charon system is considered the only binary planet in the solar system. At 1,200 kilometers in diameter, Charon is about half as wide as Pluto; the center of mass of the two bodies lies outside the surface of the dwarf planet. Pluto is also considered the closest example we have in terms of the dynamics of how planets form around binary star systems, as Scott Kenyon, a theoretical astrophysicist said.
It is believed that the pair formed at the same time, when two objects collided. Unlike most of the planets and moons orbiting the Sun, the Pluto–Charon moon system is tipped on its side, and Pluto has a retrograde orbit compared to other worlds, both suggestive of a violent beginning. The proto-Pluto and proto-Charon were likely quite different, leading to two different types of worlds. The remaining debris likely formed the other four smaller moons of Pluto.
The south pole of Charon entered polar night in 1989, and will not see sunlight again until 2107. New Horizons was able to study some of the nighttime landscape, as it was slightly illuminated by light from Pluto. The moonlight of Charon also helped scientists study Pluto once the spacecraft left the daytime side.
*Tholins: A broad class of complex organic molecules that are typically formed when ultraviolet light strikes simple organic molecules, such as methane or ethane.
References
nasa.gov
space.com