Here's a simplified timeline:
* 1930: Clyde Tombaugh discovers Pluto and it's hailed as the ninth planet in our solar system.
* Early 2000s: Astronomers begin discovering objects in the Kuiper Belt, a region beyond Neptune, that are comparable in size to Pluto. This raises questions about Pluto's planet status.
* 2005: Eris, a Kuiper Belt object larger than Pluto, is discovered. This further fuels debate about Pluto's status.
* 2006: The International Astronomical Union (IAU) defines a planet as a celestial body that:
* Orbits the Sun.
* Has enough mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
* Has cleared the neighborhood around its orbit.
* Pluto fails to meet the third criterion: Pluto shares its orbital space with other objects in the Kuiper Belt.
* August 24, 2006: The IAU votes to reclassify Pluto as a "dwarf planet" along with Eris, Ceres, and Makemake.
Therefore, Pluto was reclassified as a dwarf planet because it didn't meet the newly defined criteria for a full-fledged planet, particularly the requirement to have cleared its orbital neighborhood.
This decision sparked controversy, but it ultimately led to a more scientific and accurate understanding of the diverse objects in our solar system.
