What did the International Astronomical Union (IAU) decide about Pluto in 2006?

In 2006, the International Astronomical Union (IAU) introduced a formal definition of what constitutes a planet. As a result of this new classification, Pluto was reclassified as a dwarf planet. The decision was based on three criteria established by the IAU: a celestial body must orbit the Sun, be spherical due to its own gravity, and have "cleared the neighborhood" around its orbit. Although Pluto meets the first two criteria, it does not fulfill the third, as it shares its orbital zone with other objects of similar size in the Kuiper Belt. This significant change in classification reflects ongoing advancements in our understanding of celestial bodies and their characteristics.