What Happened to Pluto?
I suspect that everyone who was in elementary school before 2006 was forced to memorize the acronym My Very Educated Mother Just Served Us Nine Pizzas, which represented the planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune Pluto.
In 2006, it felt like they pulled the rug out from under us when they decided Pluto was no longer a planet. Who are “they”? Why did they take Pluto away from us? Was Pluto every really a planet? What did my very educated mother serve nine of???
The last question is easy: it turns out, she just made nachos instead.
For more than 100 years, scientists have been speculating about the 9th large round object from the Sun. It was officially “discovered” by scientists in 1930, although I suspect it has been around for longer than that.
You see, back then, the definition of “planet” was something that moved differently than the stars. The stars generally move very slowly and predictably, because they are so far away. Planets, since they are much, much closer, move more quickly as viewed from Earth.
However, as technology has improved over the last 100 years, scientists have identified more objects that fit that definition. In fact, hundreds of objects in and around our Solar System could fit that definition. In order to avoid a slippery slope of classifying hundreds of planets, 424 scientists in the International Astronomical Union met in Prague in 2006 to discuss the definition of a planet.
The IAU decided on a definition that would reclassify Pluto and many other large objects, such as the asteroid Ceres, as dwarf planets.
According to the IAU, a planet is a round object that has “cleared the neighborhood around its orbit”. In other words, a planet has to be big enough that any smaller objects nearby are pulled into orbit, like Earth has done with its moon. Unfortunately, Pluto didn’t make the cut because it is part of a “a sea of other objects that occupy the same region of space”. Bummer.
While Pluto was technically a planet for over 75 years, it has now been reclassified. Although Pluto itself hasn’t changed, it is now destined to be a dwarf planet forever, or until scientists decide to change some more definitions.
Interestingly, the definition change was seen as controversial to many scientists, because less than 5% of the world’s astronomers were present to vote in Prague on that fateful day in 2006. It was definitely seen as controversial to many of the world’s proponents of My Very Educated Mother[‘s]…Nine Pizzas.
Source:
https://www.space.com/2791-pluto-demoted-longer-planet-highly-controversial-definition.html