Pluto's Moons: Charon, Hydra, Nix, Kerberos and Styx

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 five moons it has orbiting it, keeping it company as it makes its long journey around the Sun. Pluto's five moons are Charon, Hydra, Nix, Kerberos and Styx.

In comparison with Pluto, Charon is quite a large moon, measuring 1,207 km in diameter (Pluto's diameter is 2,370 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 four 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, is Kerberos. It was discovered in 2011, while its fifth moon, Styx, was discovered in 2012.

Pluto and its moons may think they are alone in their quiet corner of the Solar System, but a visitor paid them a visit in 2015. The New Horizons space probe was launched in January 2006. It reached Pluto in 2015, flying by and sending back images and data about Pluto and its moons.