Sept 13th 2006 Pluto relegated to dwarf planet.
On the 13th September 2006 the planet Pluto was relegated by the International Astronomical Union to the status of a dwarf planet.
Pluto was discovered by Clyde Tombaugh in America in 1930 and became the solar system`s 9th planet. However astronomers suspected that Pluto which was a long way from the Sun and was also very small There doubts right from the beginning as to whether it was a planet or large asteroid.
In 2005 the trans neptunium object now known as Eris was discovered, it was slightly larger than Pluto. Astronomers had to decide whether to classify Eris as a planet or dwarf planet.
They decided on the latter, because they assumed many more objects the size of Eris would be discovered in the future and we could very easily end up with a solar system containing many dozens of planets.
On this basis because Eris was larger, Pluto was re classified as a dwarf planet.