Pluto was reclassified from a planet to a "dwarf planet" in 2006 by the International Astronomical Union (IAU). This decision was based on a new definition of what constitutes a planet. According to the IAU, a celestial body must meet three criteria to be considered a planet: 1. It must orbit the Sun. 2. It must be spherical in shape, due to its own gravity. 3. It must have "cleared the neighborhood" around its orbit, meaning it is gravitationally dominant and has removed most other objects in i