Many people know Pluto as one of the many Dwarf Planets in our solar system. But did you know it was once a planet? 16 years ago on August 24th, the International Astronomical Union (IAU) downgraded Pluto’s status to a Dwarf Planet, making August 24th Pluto Demoted Day.
Pluto is located on the very edge of our solar system in the Kuiper Belt. This region is located beyond Neptune and contains, in addition to Pluto, many icy objects. Pluto is the largest Dwarf Planet in our solar system but is significantly smaller than other planets. It’s even smaller than the moon.
Originally, Pluto was named the ninth planet in our solar system after its discovery in 1930. However, after more intense observations and research, scientists realized it was smaller than they thought. In addition, after the discovery of Christy, Pluto’s largest moon, scientists found that Pluto’s mass was much lighter than they assumed. Years following Pluto’s discovery, other bodies were found in the solar system that was close to, or even larger, than Pluto. These discoveries led the IAU to develop a “definition” of a planet in 2006. They defined a full sized planet as something that:
- Is in orbit around the sun.
- It has enough mass to have a round, or nearly round shape.
- Has “cleared the neighborhood” on its orbit (this means the body must be gravitationally dominant in its orbit and there are no other objects nearby that are comparable in size).
Pluto, however, only reaches numbers 1 & 2 of the criteria. Because there are still a large number of space rocks and objects in its orbit path, it has not “cleared the neighborhood.” Since Pluto’s demotion, science communities around the world recognize this historic day for Pluto.
Sources:
https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/overview/
https://www.washingtonpost.com/lifestyle/kidspost/pluto-not-a-planet/2021/08/23/ae8fd57c-fbb8-11eb-8a67-f14cd1d28e47_story.html
https://www.loc.gov/everyday-mysteries/astronomy/item/why-is-pluto-no-longer-a-planet/#:~:text=The%20International%20Astronomical%20Union%20
https://usm.maine.edu/planet/pluto-planet-again
