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How did Pluto’s discovery and later Kuiper belt discoveries lead to its reclassification?

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asteroid Ida and its satellite, Dactyl — Small body Asteroid Ida and its satellite, Dactyl, photographed by the Galileo spacecraft on August 28, 1993, from a distance of about 10,870 km (6,750 miles). Ida is about 56 km (35 miles) long and shows the irregular shape and impact craters characteristic of many asteroids. The Galileo image revealed that Ida is accompanied by a tiny companion about 1.5 km (1 mile) wide, the first proof that some asteroids have natural satellites.

Pluto was discovered in 1930 as an isolated entity, leading astronomers to initially classify it as the ninth planet. However, the subsequent discovery of the Kuiper belt in the 1990s fundamentally changed this understanding.1234

As astronomers began identifying numerous Kuiper belt objects (KBOs), it became clear that Pluto was not a unique, isolated body but rather one of the largest members of a vast population of icy debris beyond Neptune. The discovery of objects like Eris—which is similar in size to or larger than Pluto—forced the scientific community to either expand the definition of a planet to include many similar bodies or reclassify Pluto.524

In 2006, the International Astronomical Union (IAU) established a formal definition for a planet, requiring it to be massive enough to clear its orbital "neighborhood" of other objects. Because Pluto shares its region with other KBOs, it was reclassified as a dwarf planet. This decision reflects a more rigorous, scientific approach to categorizing the diverse components of our solar system.56