Plutoids

Plutoids are celestial bodies in the Solar System that orbit the Sun beyond Neptune and are massive enough for their own gravity to pull them into a nearly round shape. They are a distinct category of dwarf planet. The International Astronomical Union (IAU) established this definition in 2008. For a dwarf planet to be classified as a plutoid, it must meet two main criteria: it must orbit the Sun at a distance greater than Neptune's orbit, and it must be in hydrostatic equilibrium, meaning it has achieved a round or nearly round shape.

Currently, the known plutoids include Pluto, Eris, Makemake, and Haumea. Pluto, formerly considered the ninth planet, was reclassified as a dwarf planet in 2006, and because it orbits beyond Neptune, it also fits the definition of a plutoid. Eris, located in the scattered disc, is even more massive than Pluto. Makemake and Haumea are also located in the Kuiper Belt, a region of icy bodies beyond Neptune.

The discovery of these objects has significantly expanded our understanding of the outer Solar System. Plutoids are thought to be remnants from the formation of the Solar System, composed primarily of ice and rock. Their existence, particularly Eris, played a key role in the IAU's decision to revise the definition of a planet. The study of plutoids continues to provide insights into the conditions and processes that occurred in the early Solar System and the ongoing evolution of planetary bodies. Future discoveries are expected to identify more objects that meet the criteria for being classified as plutoids.