Beyond Neptune is a disc shaped area called the Kuiper belt named after the astronomer Gerard Kuiper. The dwarf planets Pluto and Eris lie in this far distant region of the Solar System.
From the 1930s, when it was classified, until 2006 Pluto was thought to be the ninth and smallest planet in the Solar System. But in 2005 Eris, which is 27% bigger than Pluto, was discovered deep inside the Kuiper Belt. In 2006 The International Astronomical Union decided that a new classification was needed and Pluto, Eris and the asteroid Ceres became the first dwarf planets. Haumea and Makemake are also now classified as dwarf planets.
In 2015 the New Horizons spacecraft, launched in 2008, became the first to visit Pluto and the Kuiper Belt.