Why was Pluto reclassified as a dwarf planet?

The International Astronomical Union, often abbreviated as IAU, is the global authority responsible for naming and defining celestial bodies and phenomena. Established in 1919, the IAU's mission is to promote and safeguard the science of astronomy. One of their significant roles is to establish classifications and definitions for objects in space.

In 2006, the IAU enacted a precise definition of what constitutes a planet. This came about due to the discovery of many similar-sized objects in Pluto's region, prompting the need for a clearer classification system. Their new definition of a planet includes three criteria:

• The body must orbit the Sun.
• It must be spherical in shape due to its gravity.
• It must have cleared its orbit of other debris.

These criteria led to the reclassification of Pluto, as it did not meet all the necessary conditions to be considered a full-fledged planet.

The term 'dwarf planet' was introduced by the IAU in 2006 to account for celestial bodies that share some, but not all, characteristics of the traditional planets. A dwarf planet is defined by the same first two criteria of a planet, but it does not clear its neighboring region of other objects.

Pluto fits well into this category because:

• It orbits the Sun.
• It is spherical in shape.
• However, it has not cleared its orbit of other debris in its vicinity.

Other notable dwarf planets include Eris, Haumea, and Makemake, which are also found in regions with abundant celestial debris. This classification helps astronomers better understand and organize the diverse types of bodies that inhabit our Solar System.

The Kuiper Belt is a vast region of the Solar System beyond Neptune, filled with icy bodies and remnants from the Solar System's formation. This area stretches from about 30 to 55 astronomical units (AU) from the Sun. One AU is the distance between the Earth and the Sun.

The Kuiper Belt is similar to the asteroid belt but much larger and more massive. It is home to numerous small, icy objects, along with some dwarf planets, including Pluto. These objects do not often collide but exist in a state of mutual coexistence.

Pluto's reclassification is partly due to its location in the Kuiper Belt. Unlike the eight planets which have cleared their orbits of other objects, Pluto shares its space with many other Kuiper Belt objects. This shared environment is one of the criteria that caused it to be reclassified as a dwarf planet.