Pluto was discovered in 1930 and although it is smaller than the Earth’s moon, it has 5 moons – Charon, Styx, Nix, Kerberos and Hydra. In 2006 Pluto was downgraded to a dwarf planet. This goes against what we were taught in school that Pluto is the ninth planet in our solar system.
The International Astronomical Union adapted three criteria a celestial body must meet to be classified as a planet:
- A planet must orbit a star
- A planet must have sufficient mass to create a nearly round shape
- A planet must be big enough that its gravity clears away any objects of similar size near its orbit
I do not have an issue with calling Pluto a dwarf planet, but in my opinion, it should be included as the ninth planet because it has moons orbiting it. Mercury and Venus do not have moons, but they are still classified as planets because they meet the three criteria. Pluto meets these three criteria also and should be the ninth planet.