Pluto demoted to dwarf planet 20 years ago today

On August 24, 2006, the International Astronomical Union (IAU) made a decision that would change the classification of Pluto for good. Previously, Pluto had been considered a major planet, the farthest world from the sun in our solar system. However, as technology advanced and astronomers discovered more small bodies in the outer solar system, they began to question Pluto's status.

The IAU formed a Planet Definition Committee to establish a clear definition for what constitutes a planet. They considered various options, including size and mass limits. One possibility was to include Pluto as a planet, which would also elevate Eris and Ceres to planet status. Another option was to define a planet without specific logic, but this seemed less scientific.

Ultimately, the committee defined a planet as a celestial body that orbits the sun, has enough mass for its self-gravity to shape it into a round form, and has cleared its orbit of other debris. Pluto fails this definition because it hasn't cleared its orbit of other objects. Therefore, Pluto was reclassified as a dwarf planet.

The public and some astronomers resisted the decision, calling it a demotion of Pluto. The term "Plutoed," meaning to demote or devalue, entered the global lexicon. However, as time passed, most people accepted the reclassification, which now includes a new category for celestial objects like Pluto: dwarf planets.

Today, there are approximately 10 nearly certain dwarf planets, 27 highly likely ones, 68 probable ones, 130 possible ones, and 741 that might be dwarf planets. The discovery of hundreds more undiscovered dwarf planets in the Kuiper Belt suggests that there may be up to 10,000 in that region of the outer solar system.