10 Fun Facts About Pluto's Journey From Planet to Beloved Dwarf Planet

5. The 2006 IAU Decision: Redefining Planethood

In 2006, the International Astronomical Union (IAU) convened to address the growing need for a clear and precise definition of what constitutes a planet. This meeting was prompted by the discovery of several large KBOs, including Eris, which was similar in size to Pluto. The IAU recognized that the traditional definition of a planet was no longer sufficient to encompass the diversity of celestial bodies in the solar system. After much debate, the IAU established three criteria for defining a planet: it must orbit the sun, be spherical in shape due to its own gravity, and have cleared its orbital path of other debris. Pluto met the first two criteria but failed to meet the third, as its orbit overlaps with other objects in the Kuiper Belt. As a result, Pluto was reclassified as a "dwarf planet," a decision that sparked controversy and debate among scientists and the public. The IAU's decision was a reflection of the evolving nature of science and the need to adapt our understanding as new information becomes available. While the reclassification was initially met with resistance, it ultimately provided a more accurate framework for understanding the diverse array of celestial bodies in our solar system.