Pluto
Later, in the early 21st century, the scattered disc object Eris and other objects like Pluto were discovered. Eris was initially believed to be 27% larger than Pluto, but was later found to be slightly smaller. On August 24, 2006, the International Astronomical Union (IAU) gave a definition to the word "planet" for the first time. By this definition, Pluto was not a planet anymore. It became a "dwarf planet" along with Eris and Ceres. After this, Pluto was put on the list of minor planets and was downgraded in 2006 by astronomer Michael E Brown. It was given the number 134340. Some scientists still think that Pluto should be classified as a planet.