Contrary to what Jerry Smith says in Rick and Morty, Pluto is not a planet. But why did Pluto lose this designation in 2006? The International Astronomical Union has 3 main criteria to determine what is a planet and what is not. These three criteria are: having an orbit around the sun, having sufficient mass to maintain a hydrostatic equilibrium (creating a round shape), and clearing out the space around its orbit. The main reason why Pluto is now considered a dwarf planet is because Pluto only meets two of the three criteria. While Pluto does orbit around the sun, and has enough mass to assume a spherical shape, it has not cleared out the space around its orbit. To clear out space around a planet, it must become gravitationally dominant. When a planet becomes gravitationally dominant in an area of space, it means that there are no other objects of comparable mass in the area other than a planet’s satellites. In Pluto’s case, there are objects in the Kuiper belt within Pluto’s vicinity called plutinos that are also comparable in mass. Because of the discovery of these plutinos, Pluto was downgraded to the status of dwarf planet.
Picture Source: Business Insider