What are Dwarf Planets?
Pluto
Ceres
Eris
Pluto's Moons
The Rise and Fall of Pluto
Naming Pluto
Facts about Dwarf Planets
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 four moons it has orbiting it, keeping it company as it makes its long journey around the
Sun.
Pluto's four moons are Charon, Hydra, Nix and another moon which doesn't yet
have a name.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 the way they orbit, some astronomers believe them to be a double Dwarf Planets.
Also keeping Pluto company are three 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's fourth moon, announced in July 2011 (it was first observed in June 2011), doesn't yet have a name, and is currently referred to as P4 or S/2011 (134350) 1 or S/2011 P 1. Hopefully somebody will come up with a name for it shortly! Its diameter is thought to be between 13 to 34 kilometres (8 to 21 miles). It orbits Pluto from a distance of about 59,000 kilometres (37,000 miles) and takes about 32 days to complete an orbit.
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.
