Why Pluto is not considered a planet.
Friday, 14 Mar 2025
Exclusive insights, data, and analysis for financial market experts.
Search
Have an existing account?
Sign In
Why would Pluto want to be a planet when he could be the king of the Kuiper Belt!!
It’s not a planet because it hasn’t cleaned its room.
248 years to orbit the sun? So the last time Pluto was in the same position relative to the sun it was 1776, the year the declaration of independence was signed. That’s wild.
The real reason Pluto is not a planet anymore is because we found bunch of more planetoids in the asteroid belt.
The question was “where do we draw the line”.
The easiest line was to not include Pluto.
If you think Pluto is a planet you will then need to consider if these are also planets:
Eris: https://en.wikipedia.org/wiki/Eris_(dwarf_planet)
Makemake: https://en.wikipedia.org/wiki/Makemake
Haumea: https://en.wikipedia.org/wiki/Haumea
Quaoar https://en.wikipedia.org/wiki/Quaoar
Orcus https://en.wikipedia.org/wiki/Orcus_(dwarf_planet)
Gonggong https://en.wikipedia.org/wiki/Gonggong_(dwarf_planet)
Sedna https://en.wikipedia.org/wiki/Sedna_(dwarf_planet)
Salacia https://en.wikipedia.org/wiki/120347_Salacia
(and few other potential dwarf planets)
IIRC, it also fails #1 because unlike the Earth/moon system where both bodies orbit a barycenter that’s always located within earths body, Pluto/charon orbit a barycenter outside of either body. I can’t remember if this played a factor in its demotion from planet as well, as all moons orbit a barycenter that’s within the body of the parent object.
I grew up in the 80s, and they taught us in elementary school that while Pluto was the 9th planet at the time, its status as a planet was in question and might someday change. Maybe that’s why I happily accepted the redesignation in 2006 based on the new information we had around dwarf planets.
Never thought I’d see people of science clinging to the old ways, but here we are.
This is like so many arguments about what counts as pizza. It’s not actually a debate about anything other than the definitions of words.
Ergo Neptune is also “not a planet”!
These are the criteria they came up with *after* they decided objects like Pluto shouldn’t be considered planets, but the reason they decided to change the rules to this is that they they discovered more “plutos”. It turned out pluto isn’t unique and there are many objects of that size floating around the outer solar system. If Pluto is a planet then suddenly the solar system has >15 “planets”, nobody even knows how many planets there are anymore, and a bunch of the “planets” we do know are pretty crap. This wasn’t an attractive situation to stick with, so they started working on these new rules that would exclude Pluto type objects.
Singular it’s “Criterion”.
So, Neptune is in Pluto’s way but Pluto not in Neptune’s?
The world started going downward spiral, back when Pluto got his planetary status revoked… You don’t play the Lord of the Underworld like that, without consequences, just sayin’
The worst part about demoting Pluto is that we used to be on the search for “Planet X”, and now we are looking for “Planet Nine” which sounds way less cool.
The criteria came as a result of wanting to limit the number of planets. Not because they are fundamentally different objects. I’d prefer if we classified everything a planet that has enough gravity to be round. Then we can still add subcategories for if they orbit a sun, another planet, have a cleared orbit or are rogue planets. Some of jupiters moons are larger than merkur. It feels stupid to have them in a lesser category.
Imagine wanting to limit the amount of animal species there are so that elementary school kids can learn all the animals there are. Animals that don’t dominate their ecosystem are now considered dwarf animals for this reason.
It all feels so absurdly arbitrary.
I do find it amazing that Pluto is still considered the biggest dwarf planet even though it’s smaller than the moon. Though ironically despite being the biggest it’s not the massive and that is what lead them to redefine the planets as well.
If Pluto crosses Neptune’s orbit, then Neptune hasn’t cleared it out. So…why is Neptune a planet?
Maybe we can send some rockets up there to push Pluto closer to Neptune so they collide. Then Pluto definitely won’t be a planet – or anything – anymore.
It absolutely does not cross Neptune’s orbit.
[link](https://www.astronomy.com/science/how-close-does-plutos-orbit-come-to-neptune/)
It’s also not the biggest Kuiper Belt object, that’s Eris. It IS the largest Trans-Nelptunian Object
Edit: I’m wrong. Eris is the most massive, Pluto is slightly larger by volume though
Despite what most people think, there are even several scientists that think that changing the definition of planet and Pluto’s status is pretty dumb.
Because… why? Why does it need to not be a planet? Some argue that Pluto’s size should ‘obviously’ make it not a planet. But so what that it’s small? [Even Neil DeGrasse Tyson thinks this is a bad argument](https://youtu.be/1P9cNhvA8yU?feature=shared).
The ‘it goes into Neptune’s orbit’ argument also begs the question, why does that matter? Why do planets need to be restricted into their own orbits?
Then there’s the fear that ‘there’ll be too many planets for kids to remember!!!’ Who cares? Should we limit the periodic table, amount of stars, types of penguins, etc to make it easier to remember? Science doesn’t limit its definitions because there’s too many of them.
Then there’s the definition itself. This is just a mess. For the 1st point, why does it specifically need to orbit the sun? That literally excludes exoplanets and rogue planets from being actual planets. The 2nd one is a bit vague for scientific terms, especially for geophysicists but I’d say is fine for the sake of argument. The 3rd one I don’t even think is correct [since the official IAU definition](https://www.iau.org/static/archives/releases/doc/iau0603.doc#:~:text=The%20IAU%20members%20gathered%20at,and%20(c)%20has%20cleared%20the) doesn’t mention ‘of similar size,’ so I think it’s an attempt for people to try to fix the obvious problem that Earth and Jupiter for example, almost constantly have asteroids and stuff in their orbits.
Again the problem is with that is why does it actually matter? And why do they call Pluto a dwarf planet when it isn’t even supposed to be a planet?
It seems the IAU has a pretty bad time at knowing how words and definitions work. It’s so bad they put planet in dwarf planet but also claiming dwarf planets aren’t planets.
Fortunately there’s a much better and rigorous definition called the [Geophysical definition](https://en.wikipedia.org/wiki/Geophysical_definition_of_planet) that we should use instead.
This definition is really really stupid.
Firstly, it actually says *Sun*, not star. Exoplanets are not planets by the IAU definition. There are only 8 planets in the entire universe.
Secondly, if updated modelled of the evolution of the solar system (which, fyi, include planets migrating around a fair bit) reveals that Earth’s orbit was in fact cleared by, idk, Jupiter, then Earth would not be a planet. The fact that Earth is big enough that it *could* have cleared it’s orbit had there been anything left to clear is irrelevant.
Thirdly, if there was a star orbiting the Sun that met these definitions, it would be a planet, because there’s no rule against that.
Fourth, binary planets are conceptually impossible by this definition.
I don’t care Pluto lost it’s status. I do care about this shitty set of rules. What the IAU did was decide the Solar System had 8 planets, and write a definition that counted those 8 and only those 8. What didn’t didn’t do was try any hypotheticals. The moment you subject this definition to anything other than our Solar System as it was understood in the summer of 2006 it falls flat on it’s stupid face.
Does not sweep it’s orbit clear
Sorry to be that guy, but ‘criteria’ is being used as a singular thing, but it’s the plural of ‘criterion’. You have one criterion or multiple criteria.
Almost everyone who insists that it is still a planet, is doing it purely out of emotion. No amoung of logic will change their minds, because their reasoning isn’t based on logic.
Justice for Pluto!
Nuke all the asteroids in its orbit.
If Pluto was a planet we would have to recognize Eris, which is larger than Pluto, as a planet as well.
It’s a planet to me, damnit
If Pluto is a planet then we’d have 14 since you need to include all the other dwarf planets hitting the same criteria, but you don’t see these people campaigning for Eris (which is bigger) or Ceres.
So what would happen if Pluto and Neptune actually hit each other?
Kpop group BTS wrote [a song from the POV of Pluto](https://genius.com/Genius-english-translations-bts-134340-english-translation-lyrics) after it had its planet status stripped and it’s really sad. I have a gold “name” necklace with “134340” on it. I realize it’s a bit weird to anthropomorphize a space rock, but it really resonates with me.
Pluto is, however, the official state planet of Arizona.
Bring back Pluto!