Pluto and Charon

Pluto and Charon

© NOT

It also lends its name to a class of objects known as plutoids, which are dwarf planets that circle the Sun beyond the orbit of Neptune.

Its largest moon, Charon, is almost as big as it is, as you can see from the picture. However, Pluto also has two smaller moons called Hydra and Nix. Its orbit is quite eccentric, which means that it is stretched out and not circular. Until very recently, this meant that Neptune was actually further from the Sun.

It has never been visited by a space-probe, so we know very little about it, but this will change in 2015 with the arrival of NASA's New Horizons probe.

Pluto was discovered in 1930 by Clyde Tombaugh, and until 2006 was considered to be the ninth planet.

Charon and Pluto have very strong tidal effects on each other. Because of this, Charon has a day exactly as long as the time it takes to orbit around Pluto. This means that the same side always faces Pluto, just like our own Moon.

However, because Pluto and Charon are nearly the same size, Plutos' day has also been changed so that the same side of it always faces Charon. Imagine the Moon always being in the same place in the sky over us!