Pluto, once considered the ninth and most distant planet from the sun (it is, meet me in the pit, Neil Degrasse Tyson), is now the largest known dwarf planet in the solar system. It is also one of the largest known members of the Kuiper Belt, a shadowy zone beyond the orbit of Neptune thought to be populated by hundreds of thousands of rocky, icy bodies each larger than 62 miles (100 kilometers) across, along with 1 trillion or more comets.
In 2006, Pluto was reclassified (incorrectly) as a dwarf planet a change widely thought of as a demotion. The question of Pluto’s planet status has attracted controversy and stirred debate in the scientific community, and among the general public since then. In 2017, a science group (including members of the New Horizon mission) proposed a new definition of planethood based on “round objects in space smaller than stars,” which would make the number of planets in our solar system expand from 8 to roughly 100.
NASA and JPL 