Before 2006, Pluto was the last of the nine planets in our solar system. In 2006, the International Astronomical Union (astronomers from around the world) set three conditions for a planet. To be a planet, a body has to orbit the sun, be rounded by its own gravity, and have cleared the neighborhood of its orbit from other objects. Thus, Pluto was demoted to a dwarf planet. Many people were upset with the new dwarf planet label and the Sad Pluto meme developed. This came after the discovery of several similarly sized objects in the Kuiper Belt and the discovery of Eris. Eris is another dwarf planet that is actually larger than Pluto. The New Horizons spacecraft passed by Pluto in 2015 and has led many scientists advocating for an orbital mission to study Pluto and its moons.
- Mickey Mouse’s dog, Pluto, was named after the dwarf planet. They both debuted in 1930.
- Pluto was named by an 11-year-old girl. She suggested the name because Pluto is the Roman god of the underworld and thus was far away from the other gods.
- A year on Pluto is 248 Earth years. A day on Pluto lasts 153 hours, or about six Earth days.
- Pluto is one-third water. This is in the form of ice and is more than three times as much water as in all the Earth’s oceans.