Pluto Isn't Even A Planet?! What?!

[Bartmanhomer]

Wait, are you just learning this? This was news back in like 2007.

I heard people are debating about it. I should ask why Pluto isn't a planet in the theread. No I haven't to answer your question.

[hamishspence]

Ceres is estimated to account for 1/3 the mass of the entire Asteroid Belt. It is highly doubtful that Pluto accounts for anything like 1/3 of the mass of the Kuiper Belt.

[LibraryOgre]

Indeed. Especially considering the Earth itself is not tidally locked to the Moon.

The same applies to most satellites - except the Pluto-Charon system - that's the only one where the primary is locked to the secondary and vice versa.

Isn't their barycenter also outside of Pluto by a bit?

(And does anyone remember... I thought the Sol-Jupiter barycenter was outside the sun)

[Magic_Hat]

Can I be classified as a planet? Like if Pluto is out is there an opening? Do I have to be elected?

This is Magic_Hat and I support this ad:

Are you tired of the same old boring, do nothing heavenly bodies? Are you tired of planets with only two or even one moon? I'm Magic_Hat and I believe in change. Elect me as a planet and I'll create over a dozen moon position.

[Peelee]

Isn't their barycenter also outside of Pluto by a bit?

(And does anyone remember... I thought the Sol-Jupiter barycenter was outside the sun)

I thought it was and double-checked. The Sun-Jupiter barycenter is indeed outside the Sun. Welp, time to classify Jupiter as a super planet!

Can I be classified as a planet? Like if Pluto is out is there an opening? Do I have to be elected?

Sure, I'll give you an interview right now. Question one, have you ever shot a gun in the office do you orbit the sun?

[Fyraltari]

The Moon being tidally locked to Earth and the gravitational center being within the Earth both sound like good reasons for the Moon to not be a planet, though.


There are living people who are older than Pluto's designation as a planet. Dinosaurs were discovered more than a hundred years before Pluto, and yet when scientists said "hey apparently they had feathers" it had less pushback than "we're not calling Pluto a planet anymore." You can talk about "historical weight" all you want, but in reality there's barely any historical weight behind it. That argument is basically little more than "it was a planet all my life" in fancier clothes. And that's ignoring how "it used to be that way" is an inherently poor argument to begin with.

While I agree with you, dinosaurs havign feathers is not up for debate, that's a hard fact. Pluto being a planet or not is a problem of definitions which are purely human constructs. You can't pushback against facts and call yourself a scientist but you can pushback against a decision by the scientific community.

Maybe a better parallel would be the decision to change the definition of the kilogram from "the mass of that one slab of platinium in Sèvres" to err... whatever operation you use a Kibble scale for.

[Peelee]

While I agree with you, dinosaurs havign feathers is not up for debate, that's a hard fact. Pluto being a planet or not is a problem of definitions which are purely human constructs. You can't pushback against facts and call yourself a scientist but you can pushback against a decision by the scientific community.

Yeah, I realized as I was writing it that it wasn't the best analogy, but I couldn't come up with anything else at the time so I went with it.

[Magic_Hat]

Sure, I'll give you an interview right now. Question one, have you ever shot a gun in the office do you orbit the sun?

The practice of a planet orbiting a star is outdated! The oppression of hydrogen atoms being smashed into helium must stop! If elected I will look into possible other nuclear fusion thermal-light producing energy sources.

[Peelee]

The practice of a planet orbiting a star is outdated! The oppression of hydrogen atoms being smashed into helium must stop! If elected I will look into possible other nuclear fusion thermal-light producing energy sources.

Do you agree or disagree with the following statement: All atoms are hydrogen if you take away enough protons.

Explain your answer.

[factotum]

Question one, have you ever shot a gun in the office do you orbit the sun?

Arguably, we all do...we just happen to be standing on the surface of the Earth while co-orbiting the Sun with it.

[Magic_Hat]

Do you agree or disagree with the following statement: All atoms are hydrogen if you take away enough protons.

Explain your answer.

I support the trans-atomic rights. All matter may have started out as hydrogen atoms, but if they identify as a different element I support their right to acquire more protons. The discrimination of trans-atoms must end. I also support same atom molecular marriage. If two elements that are the same wish to enter a union I support their rights.

[Lvl 2 Expert]

I thought it was and double-checked. The Sun-Jupiter barycenter is indeed outside the Sun. Welp, time to classify Jupiter as a super planet!

It's roughly 13 times too light to classify as a brown dwarf, but we could call it a grey dwarf and define the pair as a double star.

It would be a rather unorthodox pairing for having other planets orbit the primary not far outside of the secondary's orbit.

On the plus side, this would give our system a lot of new dwarf planets as Jupiter's moons are upgraded, possibly even a planet or two to compensate for the loss of Jupiter, depending on the exact orbital calculus.

Do you agree or disagree with the following statement: All atoms are hydrogen if you take away enough protons.

You'd be left with rather exotic isotopes.

Do you figure with could stuff in so many neutrons that the electron hits them and crashes? What would take take, an atomic mass of a few billion mu?

[Morty]

I've never seen what the big deal is with Pluto being a planet. Scientific definitions change when they need to. Or when one idea prevails over another for some reason. Either way it's nothing to take personally.

[Peelee]

Arguably, we all do...we just happen to be standing on the surface of the Earth while co-orbiting the Sun with it.

That's like saying technically the moon or its the sun, it just does it while also orbiting the earth.

[Manga Shoggoth]

I've never seen what the big deal is with Pluto being a planet. Scientific definitions change when they need to. Or when one idea prevails over another for some reason. Either way it's nothing to take personally.

It's not as if words don't change their meaning over time, or are used differently by different groups. I mean, how many people use velocity as a synonym for speed?

It's just that with velocity the precise scientific term was watered down in popular culture, and most people didn't notice or care, while here the loose definition of planet is being tightened up a little and everyone noticed and some people got in a tizzy.

Do you agree or disagree with the following statement: All atoms are hydrogen if you take away enough protons.

Did you get a charge out of asking this question?

[LibraryOgre]

Do you agree or disagree with the following statement: All atoms are hydrogen if you take away enough protons.

Explain your answer.

Did you get a charge out of asking this question?

Why do you have to be so negative?

[halfeye]

I've never seen what the big deal is with Pluto being a planet. Scientific definitions change when they need to. Or when one idea prevails over another for some reason. Either way it's nothing to take personally.

I don't have a problem with Pluto not being a planet, it was a bit of a surprise, but I got over it.

The problem is the silly definition they used to do it. That would make Jupiter a minor planet if it was orbiting far enough out, and that is not even close to sensible.

[georgie_leech]

I don't have a problem with Pluto not being a planet, it was a bit of a surprise, but I got over it.

The problem is the silly definition they used to do it. That would make Jupiter a minor planet if it was orbiting far enough out, and that is not even close to sensible.

I mean, yeah? If Jupiter was out in the Kuiper Belt and the Kuiper Belt was still a thing, Jupiter wouldn't have cleared its orbit enough to be a planet. Assuming that Jupiter wouldn't have been massive enough to actually clear out its orbit anyway. Seems to me that orbital mechanics being as complex as they are, you couldn't just shift Jupiter elsewhere in the Solar system without it having at least local effects.

[LibraryOgre]

I mean, yeah? If Jupiter was out in the Kuiper Belt and the Kuiper Belt was still a thing, Jupiter wouldn't have cleared its orbit enough to be a planet. Assuming that Jupiter wouldn't have been massive enough to actually clear out its orbit anyway. Seems to me that orbital mechanics being as complex as they are, you couldn't just shift Jupiter elsewhere in the Solar system without it having at least local effects.

As I understand it, a Kuiper Jupiter, with no corresponding Outer Solar System Jupiter, would've likely heavily screwed over Earth. The process of clearing its orbit would've flung comets all over the place, without the OSS Jupiter there to catch them and keep them from going further.

Jupiter is the solar system's goalie. Earth is a small child that has wandered into the goal box, whose head would be crushed by incoming comets and asteroids.

[halfeye]

I mean, yeah? If Jupiter was out in the Kuiper Belt and the Kuiper Belt was still a thing, Jupiter wouldn't have cleared its orbit enough to be a planet. Assuming that Jupiter wouldn't have been massive enough to actually clear out its orbit anyway. Seems to me that orbital mechanics being as complex as they are, you couldn't just shift Jupiter elsewhere in the Solar system without it having at least local effects.

I believe Pluto is in the Kuiper belt? Jupiter would need to be further out than Pluto currently is to fail to clear its orbit.

As I understand it, a Kuiper Jupiter, with no corresponding Outer Solar System Jupiter, would've likely heavily screwed over Earth. The process of clearing its orbit would've flung comets all over the place, without the OSS Jupiter there to catch them and keep them from going further.

Jupiter is the solar system's goalie. Earth is a small child that has wandered into the goal box, whose head would be crushed by incoming comets and asteroids.

I suspect that's not exactly right, a lot of stuff does miss Jupiter, the extra-solar visitors for two. However, I'm not proposing moving Jupiter, just pointing out that if it was orbiting the sun at four or five times Pluto's orbital radius, by this definition of minor planet it would be one. Which I suggest makes this definition absurd.

[Peelee]

I'm not proposing moving Jupiter, just pointing out that if it was orbiting the sun at four or five times Pluto's orbital radius, by this definition of minor planet it would be one.

...so? Is Jupiter, or any other planet that is no longer a planet because it's that far out, that far out? By the IAU definition, if I curled into a ball and teleported halfway between Mercury and Venus, I would count as a planet. That doesn't make the definition absurd, that makes my hypothetical absurd.

[hamishspence]

For Jupiter to be considered to have "failed to clear its orbit" there would need to be multiple comparable objects in that zone.

The existence of the Trojans, doesn't mean that Jupiter has failed to clear its orbit - the job done is good enough.

Supposing the hypothetical Neptune-sized planet in the Kuiper belt

https://en.wikipedia.org/wiki/Planet_Nine

turns out to actually exist - it would be considered a planet rather than a minor planet - because it's by far the biggest thing Out There.

[weckar]

Indeed. Especially considering the Earth itself is not tidally locked to the Moon.

Yasaywhat? Ever seen the moonless-Earth orbital model?

[hamishspence]

Yasaywhat? Ever seen the moonless-Earth orbital model?

I mean that the earth takes 1 day to rotate, and the moon takes 28 days to orbit. If the Earth was tidally locked to the Moon, then, like the Moon, it would keep the same face turned to its partner at all times.

Pluto-Charon is exactly this. Moon tidally locked to planet, and planet tidally locked to moon.

Similarly, all four Galilean moons are tidally locked to Jupiter - but Jupiter is not tidally locked to them.

[Fat Rooster]

Best way of expressing gravitationally dominant I have found is "does this belong on a map for navigation?". All the 'proper' planets cannot be ignored if you are plotting trajectories over medium to long timescales. The distance to the sun has an impact on this, which is why Mercury can be considered a planet when the same object further out could not be. An object at a similar distance will in a reasonable timescale have an encounter with Mercury close enough to radically alter it's orbit. Further out this would not be the case, as there is so much more room and things happen so much slower.

We can track the trajectories of almost all trans neptunian objects just fine while ignoring Pluto, so it does not need to be marked on our map. That means it is not a Planet.

In contrast, something else seems to be 'herding' things out there, throwing them into weird orbits. An object that is doing that does belong on our map, which is why we refer to it as Planet 9, even though we haven't actually found it. It has recently been suggested that it might be a black hole, and then we run into the question of whether that would count as a planet, as it seems to fit the definition!

[Lord Torath]

As I understand it, a Kuiper Jupiter, with no corresponding Outer Solar System Jupiter, would've likely heavily screwed over Earth. The process of clearing its orbit would've flung comets all over the place, without the OSS Jupiter there to catch them and keep them from going further.

Jupiter is the solar system's goalie. Earth is a small child that has wandered into the goal box, whose head would be crushed by incoming comets and asteroids.

It depends on who you ask. I've seen several articles suggesting that Jupiter sends just as many asteroids/comets into the inner solar system as it sends outward.

And as Fat Rooster says, we haven't yet found Planet 9. It's hypothetical until we do.

[jayem]

...so? Is Jupiter, or any other planet that is no longer a planet because it's that far out, that far out? By the IAU definition, if I curled into a ball and teleported halfway between Mercury and Venus, I would count as a planet. That doesn't make the definition absurd, that makes my hypothetical absurd.

It's a hypothetical that I think needs a sensible answer.
We're seeing enough other Solar systems that it's going to become relevant.

An answer of "No, and we're perfectly fine with that because ..." which Fat Rooster's argument nearly does (enough for me to believe the actual people responsible have an argument), is however perfectly valid.
Anything size based is going to run into issues with including Moons or excluding Star-orbiting objects (Mercury). So I think long term, size, composition and orbit will have to be dealt with separately.

[Peelee]

Frankly, I think the surface gravity would be an excellent metric. It would certainly disqualify Planet Peelee.

[weckar]

I mean that the earth takes 1 day to rotate, and the moon takes 28 days to orbit. If the Earth was tidally locked to the Moon, then, like the Moon, it would keep the same face turned to its partner at all times.

Pluto-Charon is exactly this. Moon tidally locked to planet, and planet tidally locked to moon.

Similarly, all four Galilean moons are tidally locked to Jupiter - but Jupiter is not tidally locked to them.

My apologies, I confused tidal lock with OPD. It is generally more accurate to say that as a binary system Earth and Moon have cleared their orbit, after all.

[hamishspence]

I get the impression that even if the Moon wasn't there, the Earth is still big enough to qualify as dominating its zone, and the clearing-out process would still have taken place.

So, the Earth on its own would have qualified as a planet - it doesn't need the Moon to do its job.