Pluto and its moons. Illustration of the dwarf planet Pluto (upper right, orange) and its largest moon Charon (grey, upper left), with two smaller moons. One of the smaller moons (Hydra) dominates the foreground of this image. The other one (Nix) is seen near Pluto. Nix and Hydra were discovered in June 2005. Nix is around 42 kilometres long, and Hydra is around 55 kilometres long. Charon has a radius of around 1200 kilometres. Pluto's diameter is around 2370 kilometres.