Artwork of the dwarf planet Pluto and its system of moons. Pluto is a dwarf planet on the inner edge of the Kuiper belt - a region of icy debris surrounding the Sun. Its largest and innermost moon, Charon, has been known about since 1977. In 2005, astronomers discovered two additional moons, much smaller than Charon, called Nix and Hydra. A fourth moon, Kerberos, was found in 2011. Then in 2012, Styx brought the total number of known satellites to five. This image shows Pluto (centre) with these five known satellites. From the centre outwards they are Charon, Styx, Nix, Kerberos and Hydra. Pluto and Charon are shown to scale relative to each other and to the sizes of their orbits. The other moons are shown much larger than their comparative sizes, for clarity.