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This should be pretty obvious for long-time Sailor Moon fans and indeed for anyone who was born before the 2000s. Pluto was considered a planet for over 70 years and there are several reasons for why that was. First off even though Pluto is very distant Pluto is still very bright. This is in part due to Charon, Pluto's very large moon. It was because of this that for a long time Pluto was considered to be a Mercury-sized or even a Mars-sized planet. However with recent scientific tools we've discovered that Pluto is much smaller than Mercury and this was something that lead to its demotion. The other thing that lead to Pluto's demotion was the discovery of Eris that demanded a definition for 'Planet' be made. Sailor Moon of course was created n 1992 long before many modern day celestial objects were discovered.
Believe it or not there have been many debates through out human history as what constituted a 'Planet'. For example the Galilieian moons (Jupiter's 4 largest moons) were considered planets at one time, along with Ceres which in modern day is the only dwarf planet that orbits the sun in the Asteroid Belt between Mars and Jupiter. We finally got a solid definition of what made a planet in 2006 for the first time in human history. To put it simply Pluto didn't make the cut. A planet is an object that a) orbits the sun, b) is round in shape, and c) is gravitationally dominant.
Let's look at that above definition and see how Pluto holds up. Pluto definitely orbits the sun directly, there's no doubt about that as it doesn't orbit any other type of body besides the sun. Pluto is wonderfully round in shape, the Hubble Space Telescope tells us that much even with our rather limited pictures. However where Pluto hits a snag is the gravitationally dominant part. Pluto is simply not large enough to pick up, clear, or capture the rest of the objects that orbit around the same area Pluto does. To put it as simply as I can, Pluto's orbit is cluttered with lots of stuff that the gravitationally dominant planets don't have to deal with. The main 8 planets simply have more control over their orbits then Pluto and Pluto's fellow dwarf planets.
As we've discovered more and more celestial objects over time we've learned something rather shocking. Pluto isn't alone! In fact our solar system is home to MANY Pluto-like objects! Eris, Pluto, Haumea, Makemake and Ceres are currently recognized officially by the International Astronomy Union (IAU) as dwarf planets. However there are hundreds - if not thousands - of unofficial and mostly undiscovered and unexplored dwarf planets right in our solar back yard. Examples of yet-unofficial dwarf planets include Sedna, Quaour, and Orcus. Due to the large amount of these objects the IAU decided it would be better to group all those Pluto-like objects together in one group to their own instead of grouping them in with the 8 main planets. This decision was obviously controversial and rustled many jimmies.
So you get why Pluto isn't a planet, even if you don't agree with it. So as a Sailor Moon fan, what does this mean? Does this change anything for Sailor Pluto? Nope. When most people think of Sailor Moon they think of the anime and they think of the main Sailor Senshi that guard the planets of our solar system. That's all fine and good, however when you turn instead to the Sailor Moon manga and think of Sailor Senshi that come from our solar system you find 4 curious new sailors that never made it into the anime. I'm talking about Sailor Ceres, Sailor Pallas, Sailor Juno and Sailor Vesta. Now Sailor Ceres I've already mentioned before, Ceres is a dwarf planet along with Pluto. Yeah that's right, we had 2 dwarf planet sailor senshi all along! Pallas, Juno, and Vesta are all objects that are much smaller than Pluto and are already canon senshi, long before the definition of a planet was made. To put it simply there are MANY different Sailor Senshi in Sailor Moon canon besides just planetary ones. So calm down, breathe, it'll be alright. I'm sure Pluto isn't leaving the hearts and minds of your fellow Moonies anytime soon.
Why is Pluto a Sailor Senshi?
This should be pretty obvious for long-time Sailor Moon fans and indeed for anyone who was born before the 2000s. Pluto was considered a planet for over 70 years and there are several reasons for why that was. First off even though Pluto is very distant Pluto is still very bright. This is in part due to Charon, Pluto's very large moon. It was because of this that for a long time Pluto was considered to be a Mercury-sized or even a Mars-sized planet. However with recent scientific tools we've discovered that Pluto is much smaller than Mercury and this was something that lead to its demotion. The other thing that lead to Pluto's demotion was the discovery of Eris that demanded a definition for 'Planet' be made. Sailor Moon of course was created n 1992 long before many modern day celestial objects were discovered.
So what is a planet then?
Believe it or not there have been many debates through out human history as what constituted a 'Planet'. For example the Galilieian moons (Jupiter's 4 largest moons) were considered planets at one time, along with Ceres which in modern day is the only dwarf planet that orbits the sun in the Asteroid Belt between Mars and Jupiter. We finally got a solid definition of what made a planet in 2006 for the first time in human history. To put it simply Pluto didn't make the cut. A planet is an object that a) orbits the sun, b) is round in shape, and c) is gravitationally dominant.
So why isn't PLUTO a planet!?!
Let's look at that above definition and see how Pluto holds up. Pluto definitely orbits the sun directly, there's no doubt about that as it doesn't orbit any other type of body besides the sun. Pluto is wonderfully round in shape, the Hubble Space Telescope tells us that much even with our rather limited pictures. However where Pluto hits a snag is the gravitationally dominant part. Pluto is simply not large enough to pick up, clear, or capture the rest of the objects that orbit around the same area Pluto does. To put it as simply as I can, Pluto's orbit is cluttered with lots of stuff that the gravitationally dominant planets don't have to deal with. The main 8 planets simply have more control over their orbits then Pluto and Pluto's fellow dwarf planets.
So what's the 'dwarf planet' stuff about?
As we've discovered more and more celestial objects over time we've learned something rather shocking. Pluto isn't alone! In fact our solar system is home to MANY Pluto-like objects! Eris, Pluto, Haumea, Makemake and Ceres are currently recognized officially by the International Astronomy Union (IAU) as dwarf planets. However there are hundreds - if not thousands - of unofficial and mostly undiscovered and unexplored dwarf planets right in our solar back yard. Examples of yet-unofficial dwarf planets include Sedna, Quaour, and Orcus. Due to the large amount of these objects the IAU decided it would be better to group all those Pluto-like objects together in one group to their own instead of grouping them in with the 8 main planets. This decision was obviously controversial and rustled many jimmies.
Why should Pluto STILL be a Sailor Senshi?
So you get why Pluto isn't a planet, even if you don't agree with it. So as a Sailor Moon fan, what does this mean? Does this change anything for Sailor Pluto? Nope. When most people think of Sailor Moon they think of the anime and they think of the main Sailor Senshi that guard the planets of our solar system. That's all fine and good, however when you turn instead to the Sailor Moon manga and think of Sailor Senshi that come from our solar system you find 4 curious new sailors that never made it into the anime. I'm talking about Sailor Ceres, Sailor Pallas, Sailor Juno and Sailor Vesta. Now Sailor Ceres I've already mentioned before, Ceres is a dwarf planet along with Pluto. Yeah that's right, we had 2 dwarf planet sailor senshi all along! Pallas, Juno, and Vesta are all objects that are much smaller than Pluto and are already canon senshi, long before the definition of a planet was made. To put it simply there are MANY different Sailor Senshi in Sailor Moon canon besides just planetary ones. So calm down, breathe, it'll be alright. I'm sure Pluto isn't leaving the hearts and minds of your fellow Moonies anytime soon.
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