[Shasown]

Originally Posted by joeysteele

I wasn't happy when they demoted Pluto, who suddenly makes that decision after all these decades and centuries.

In the late 20th and early 21st century, many objects similar to Pluto were discovered in the outer Solar System, minor planet Chiron in 1976 disc object Eris in 2005, which is a lot larger than Pluto.

In 2006, the International Astronomical Union (IAU) defined what it means to be a "planet" within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category "dwarf planet" along with Eris Chiron and Ceres.

After the reclassification, Pluto was added to the list of minor planets and given the number 134340

Saying that there are some groups of astronomers, physicists etc who still regard Pluto as a major planet.