Pluto was originally discovered by Clyde Tombaugh in 1930 and was considered to be the ninth planet from the Sun. However, things changed after 1992, when the planethood of Pluto was questioned. Several other objects of similar size were discovered in the Kuiper belt, leading to the International Astronomical Union redefining the term “planet”.
All things considered, Pluto is the largest planet orbiting the Sun. But the planet was also named “dwarf planet” because of its size. Since 2006, Pluto is reclassified as dwarf planet, leading to jokes about the Planet.
This documentary fully explores the reasoning why Pluto is not a planet, and how we got to the point to call Pluto a “dwarf planet”.