PLUTO'S MOONS

One thing that every planet needs is companionship! Dwarf Planet Pluto, many many millions of miles away from the Sun, would be a tiny lonely world if it wasn't for the three moons it has orbiting it, keeping it company as it makes its long journey around the Sun. First there is Charon. Despite Pluto being discovered in 1930, it took another 48 years until Charon was found. James Christy found the moon on 22nd June 1978. The name Charon was chosen because in Greek mythology, Charon was the ferryman of the dead (linking in with Pluto being the God of the Underworld). In mythology, Charon is pronounced "Karon" but James Christy pronounced it with a softer "Sh" sound, meaning that his moon is pronounced "Sharon"! The reason he chose this pronunciation of the name is because of his wife's name, Charlene, who was nicknamed "Char". 

In comparison with Pluto, Charon is quite a large moon, measuring 1,212 km in diameter (Pluto's diameter is 2,280 km). Most moons are many times smaller than the body they orbit. Charon also orbits closely to Pluto, only 19,640 kilometres away from the planet. Only Mars has a moon which orbits its planet even closer (Phobos at 9,270 kilometres). Compare that to Earth's moon which orbits Earth at a distance of 384,400 km. Unlike other moons, Charon and Pluto appear to orbit around each other, as if there is an invisible axis in between the two objects. They take only six days to complete an orbit around this axis. Because of the sizes of Pluto and Charon, their closeness to each other, and they way they orbit, some astronomers believe them to be a double Dwarf Planets.  

Also keeping Pluto company are two much smaller moons. The discovery of Hydra and Nix was announced in October 2005. Hydra orbits Pluto at a distance of 65,000 km, taking about 38 days to complete an orbit. Nix orbits at a distance of about 42,000 km, taking almost 25 days to complete an orbit. The sizes of the two moons are not yet known, although they are expected to be no smaller than 44 km in diameter and no larger than 130 km, with Nix thought to be the smaller of the pair. In Greek mythology, Hydra is a monster who guards the waters of Pluto's underworld. Nix is the Greek goddess of darkness and night and the mother of Charon. So, they seem like quite a normal family! 

Pluto and its moons may think they are alone in their quiet corner of the Solar System, but a visitor is on its way! The New Horizons space probe was launched in January 2006. It is due to reach Pluto in 2015. It will complete fly by missions of Pluto, Charon, Hydra and Nix, sending back images and data about these mysterious worlds.