Charon is the largest moon or ‘satellite’ of the former planet Pluto (discovered in 1930) which was classed as our solar system’s ninth planet until 2006; Charon is also the 22nd largest body in the solar system. There has been debate in the scientific community about whether, in fact Charon is actually a moon or if Pluto and Charon are a double planet system. Charon has a diameter just over half that of Pluto making it a sizable companion. It is a widely held belief that it was formed by a giant collision with Pluto much like our own moon was formed by a collision with Earth.
Charon was discovered on June 22, 1978 by the astronomer James Christywhile he was studying highly magnified images of Pluto on photographic plates. Christy noticed that a minor elongation appeared every so often, other previously taken plates were then examined to see if the same anomaly appeared and indeed the bulge was confirmed on plates dating back to April 29, 1965. Since then Charon and Pluto have been studied in far greater detail, in 2005 there was a discovery of two other , smaller natural satellites of Pluto (Hydra and Nix) and although no missions have been sent yet, the ‘New Horizons’ mission is scheduled to visit Charon and Pluto in the year 2015.
What about the geological make up of Charon? The surface of seems to be dominated by water ice, and there also appears to be no atmosphere, it is a largely icy body and is thought to contain less rock by proportion than Pluto itself. In 2007, studies by the Gemini Observatory showed patches of ammonia hydrates and water crystals on the surface suggesting the presence of active ‘cryo-geysers’ which are fed by volcanoes that erupt substances like water, ammonia and methane, instead of molten rock like volcanoes here on Earth. The interior make up of Charon obviously cannot be confirmed, but some scientists think it is a differentiated body like Pluto with a rocky core and an icy mantle while others believe it is of uniform composition throughout.
When it was discovered, Christy suggested the name Charon as a scientific version of his wife Charlene’s nickname, ‘Char’, however Charon is also the name of the mythological ferryman of the dead, closely linked with the god Hades with whom the Romans associated with their god Pluto so the name was an obvious match. Officially the name was adopted in late 1985.