Pluto: Planet or Dwarf?
Why Was Pluto Demoted?
When I was growing up, we were taught that there were 9 planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Pluto, we were taught, was discovered in the 1930s. When I was going to school, Pluto was thought to have no moons, later they found a moon and named it Charon (after the "ferryman" in mythology who ferried the dead to Hades). Since then, Nix and Hydra and two other moons have been discovered. So how is it that something substantial enough to have at least 5 moons was demoted to a "dwarf planet"?
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So What's the Issue?
So, as a good fan of the planet Pluto, I went to find out what the issue was. Why were they demoting my favorite little planet?
Well, apparently the scientists who work on these sorts of things (Astronomers) found some planetary type bodies in our Solar System. One of the planetary objects they found was named Eris. Eris, strangely enough, is larger than Pluto. But is that enough to change Pluto's status?
Why was Pluto demoted? Why didn't they promote Eris? Ceres, another planetary body, is now also considered a Dwarf Planet, but Ceres is a bit smaller than Pluto and Eris. When I was in school, I recall Ceres being considered an Asteroid. Asteroids are sometimes irregularly shaped, so perhaps that is why Ceres was promoted to a Dwarf Planet.
So where do we stand with planetary bodies? What constitutes a planet and what constitutes a Dwarf Planet? And, by the way, what constitutes an Asteroid? While many of the Asteroids are in the Asteroid Belt between Mars and Jupiter, there are some that are not.
Because space is so vast and there are so few objects within that vastness, I highly doubt that we are done finding planetary bodies or categorizing them. Like living organisms on the earth, planets and planetary bodies change over time; they change their position in the sky, they change their sizes and compositions, they change their place vis-a-vis the sun. We will continue learning about the solar system; we will continue to learn about the entire universe.
The Planets as I Learned Them
While I know Pluto is no longer a planet, this is how I learned it.