Is Pluto a planet? (Pluto discussion thread, if there isn't already one)

[Royalswissarmyknife]

and Wyoming doesn't exist this is obviously a fake image

[lajoswinkler]

Decisively NO.

I remember back in the middle of 90s when my geography teacher said including Pluto among the planets has been a mistake and that soon we'll have enough data to finally remove it from the set. Dumb pride was pretty much the only reason we were clinging to the idea of it being a planet. Italy did not squeal when Ceres was demoted, but you can't hear the end of it from USA even today about Pluto. It got tiresome after five minutes and it's super annoying in 2023.

Planets, satellites, dwarf planets, comets, asteroids, are all planetary bodies - they don't do fusion and are thus set apart from stellar bodies which include stars as the most famous members. Classification is elegant and has to exist to make order in the chaos around us. The only thing I dislike here is the name dwarf planet which semantically implies a subset of planets and they stand as a separate category. Planetoid would be a way better name.

The idea pushed by some American planetary geologists (you know who I'm talking about... those annoying folks in the New Horizons team who keep lying "wE hAd AbSoLuTeLy No IdEa pLuTo wiLL LoOk LiKe tHaT" despite our data on Triton and cryogeology models; Jim Green and Alan Stern, I'm looking at you!) to call all rounded things planets is just ridiculous and stems from the desperate need to remain part of the team that was first to visit a specific planet. 

There is no sound and scientific reason to twist the classification like that. It would be an insult to the astronomical community. I don't hate Pluto, I love it, but this whole thing is so forced and ridiculous.

[Bej Kerman]

If Pluto is a planet, all the other millions of similarly sized bodies in the Kuiper belt are planets. If it just has to be solid and orbit the Sun, then J002E3, a spent S-IVB stage, is a planet.

[kerbiloid]

https://en.wikipedia.org/wiki/Titius–Bode_law

m	k	T–B rule distance (AU)	Planet	Semimajor axis (AU)	Deviation from prediction1
−∞	0	0.4	Mercury	0.39	−3.23%
0	1	0.7	Venus	0.72	+3.33%
1	2	1.0	Earth	1.00	0.00%
2	4	1.6	Mars	1.52	−4.77%
3	8	2.8	Ceres2	2.77	−1.16%
4	16	5.2	Jupiter	5.20	+0.05%
5	32	10.0	Saturn	9.58	−4.42%
6	64	19.6	Uranus	19.22	−1.95%
–	–	–	Neptune	30.07	–
7	128	38.8	Pluto2	39.48	+1.02%

Pluto is a Neptune placeholder, it's not a planet itself.

***

Later the enormous gravity of Pluto will pull Neptune to its legal orbit.

[RCgothic]

I don't really care whether Pluto is it isn't a planet, but I think the logic by which Pluto has been declared *not a planet* is unsound. Earth transposed to Pluto's orbit wouldn't have "cleared its neighborhood" because it would still be in the neighborhood of Neptune. A definition that depends on location is a bad definition.

[Jacke]

Pluto isn't a planet for the same reasons Ceres isn't a planet.  Both were in a band of orbits where they were the first and near largest object discovered.  But eventually many more similar and smaller objects were discovered in similar orbits.  If they are planets, then there are thousands of planets.  They are in the same class as Jupiter and Earth.  Thus the new definition of planet.  It makes the class of objects called planets useful.

[RCgothic]

I don't see the problem with having thousands of planets if there are thousands of gravitationally rounded objects.

But even if a distinction must be drawn, draw it with a criteria that wouldn't exclude the things that are called planets if their orbits were slightly different. Degree of roundedness. Stratification of core. Something intrinsic to the body and not its arbitrary position in space.

Pluto would be a planet swapped with Mercury. Earth wouldn't be if transplanted to Pluto's orbit. It's the criterion I object to more than the categorisation.

[NFUN]

3 hours ago, RCgothic said:

I don't really care whether Pluto is it isn't a planet, but I think the logic by which Pluto has been declared *not a planet* is unsound. Earth transposed to Pluto's orbit wouldn't have "cleared its neighborhood" because it would still be in the neighborhood of Neptune. A definition that depends on location is a bad definition.

The Moon, Ganymede, Titan, Europa, Callisto, Io, Enceladus, etc are planets?

[kerbiloid]

If place Jupiter into Oort cloud (if the latter exists), it wouldn't clean its orbit, because the orbital period would be comparable to the Solar System lifespan, and relative speeds are in meters per second.

Ergo, when Jupiter is where it is, it's a planet.

If put it farther, it stops being a planet.

[Davi SDF]

Isn't "clean orbit" used to mean that "said object's mass is over 50% or so larger than anything else that crosses or follows said orbit?" 

 

If that's the case, then yes, Earth if placed in Pluto's orbit will be a dwarf planet (thanks to Neptune).  But if Pluto was placed in Earth's orbit (without the Moon in it, of course), then it could probably be a planet. I dunno about you, but that seems about right to me. 

 

So, no, Pluto isn't a planet, but it is a dwarf planet. I don't see why it should be anything else. 

[lajoswinkler]

16 hours ago, RCgothic said:

Earth transposed to Pluto's orbit wouldn't have "cleared its neighborhood" because it would still be in the neighborhood of Neptune.

But it's not. And that's where the story ends.

[kerbiloid]

12 hours ago, Davi SDF said:

Earth if placed in Pluto's orbit will be a dwarf planet (thanks to Neptune). 

It would be cleaned by Neptune very soon, because the orbit is short.
So, a billion years later nobody would even know about the former Earth.

But if put Jupiter and Saturn on the same Oort-high orbit, they will unlikely ever affect each other, because every orbit will take many million years.
So, both Jup and Sat won't be legal planets.

[razark]

Planet?  There's no planet around here.

 

[kerbiloid]

This explains why Charon is so big.

[ProtoJeb21]

I feel like the term "dwarf planet" needs retooling. Pretty much any spherical object in the Kuiper Belt can be counted as a dwarf planet - gravitationally rounded bodies that haven't fully cleared their orbits - but the truth probably isn't that simple. A 2019 paper (Grundy et al. 2019) on a ~600 km KBO whose name I won't even attempt to try and spell concluded that some KBOs below 900-1000 km in diameter may not be fully differentiated and exhibit internal porosity. If that's the case, then the largest dwarf planets like Pluto, Eris, pre-impact Haumea, Makemake, Quaoar, and Gonggong are massive enough to both collapse into a sphere and have differentiated interiors, while many sub-900 km dwarf planets/KBOs may be rounded but undifferentiated. This may finally be a lower size limit on what can be considered planets and I think should be incorporated into the definitions of planets and dwarf planets. 

I'd argue that internal differentiation is a more important classification criteria than orbital clearing, not just because the definition of latter is vague and arbitrarily excludes pretty much every major planet (asteroids cross their orbits so technically they violate that criteria), but because it isn't really about the properties of the object itself. Rather, it's based on the object in comparison with its surroundings. Internal differentiation is a key characteristic of an object's structure and formation, is easy to understand, and can set a hard lower limit for planets or dwarf planets. I think the best options are to set a dividing line at 900-1000 km, and either make all the dwarf planets above that into major planets, or demote all the dwarf planet candidates below that into their own new category of KBO/SSSO.

As for Pluto, I think there's decent justification for upgrading back to a planet. Even with my suggested internal differentiation criteria, whether Pluto would officially get upgraded to a planet or not depends if the IAU ever does anything about the orbital clearing criteria.

Edited February 26, 2023 by ProtoJeb21

[kerbiloid]

Btw.
The Pluto orbit is highly eccentric and intersects the Neptunian one.

That means that Neptune hadn't cleared its orbit at least from Pluto, and thus Neptune is not a planet.

[tomf]

Neptune and Pluto have a 3:2 orbit resonance so can never colide so you can argue that they don't share an orbit.

But the real reason is because Neptune is 8000 times more massive than the most massive thing that crosses is orbit.

[NFUN]

45 minutes ago, tomf said:

Neptune and Pluto have a 3:2 orbit resonance so can never colide so you can argue that they don't share an orbit.

But the real reason is because Neptune is 8000 times more massive than the most massive thing that crosses is orbit.

kerbiloid knows and has heard all of this before but he has honed his disingenuity to an art form

[kerbiloid]

8 hours ago, tomf said:

Neptune and Pluto have a 3:2 orbit resonance so can never colide so you can argue that they don't share an orbit.

Earth was also thinking so, before something big hit the fan, after drifting from the Lagrange point where it was in 1:1 resonance.

No resonance can be stable forever, and also to become resonant, their orbits originally had to be not resonant.

Sooner or later either rounding error or Sun expansion (and mass loss) will bring Pluto a little cloer to Neptune, and there will be no resonance between them, only fear and loathing.

8 hours ago, tomf said:

But the real reason is because Neptune is 8000 times more massive than the most massive thing that crosses is orbit.

The "clear orbit" criterion has no concrete limit value.

7 hours ago, NFUN said:

kerbiloid knows and has heard all of this before but he has honed his disingenuity to an art form

He's just looking at the Moon above.

Some time ago it was floating at Lagrange point, which is even more hardcore resonant due to the Sun gravity.

Edited March 4, 2023 by kerbiloid

[Jacke]

2 hours ago, kerbiloid said:

Earth was also thinking so, before something big hit the fan, after drifting from the Lagrange point where it was in 1:1 resonance.

Earth does have a resonance.  With Venus.  At inferior conjunction, the same side of Venus faces the Earth.  Explain that one.

 

2 hours ago, kerbiloid said:

No resonance can be stable forever, and also to become resonant, their orbits originally had to be not resonant.

Yes a resonance can be effectively stable for a very long time under the right conditions.  It's like the Lagrande points L₄ and L₅, which, if the ratio of the two masses of the larger objects, M1/M2, is greater than 24.96, are stable for masses much much smaller than both.  Because if a small mass at those points moves away from them, the effective perturbing gravitation pushes them back towards the point.

 

2 hours ago, kerbiloid said:

Sooner or later either rounding error or Sun expansion (and mass loss) will bring Pluto a little cloer to Neptune, and there will be no resonance between them, only fear and loathing.

The Sun won't lose significant mass before it evolves into a Red Giant, perhaps not even that much then.  And Red Giant expansion won't happen for a long time.  Right now, there's only the usual Main Sequence Brightening, which proceeds slowly without much radius change.

Pluto and Neptune are more than just in a 3:2 resonance.  Because of the eccentricity and relative inclination of Pluto's orbit, the two orbits aren't even close.  And the perturbing effects of Jupiter and Saturn aren't enough to change that.

 

2 hours ago, kerbiloid said:

The "clear orbit" criterion has no concrete limit value.

It's the end of a process that is rather obvious once at the end.  There are 8 planets who have cleared their orbits.  Pluto, like Ceres, is just the largest of a whole class of smaller bodies of similar size to themselves in similar orbits.  They have not cleared their orbits.  Because they are large enough to form into a sphere, they are minor planets.

 

2 hours ago, kerbiloid said:

He's just looking at the Moon above.

I don't think you're referring to @NFUN.   Are you referring to yourself in the 3rd person?  Really?

 

2 hours ago, kerbiloid said:

Some time ago it was floating at Lagrange point, which is even more hardcore resonant due to the Sun gravity.

Are you talking about Theia?  That's not the Moon.  And Earth's Lagrande points L₄ and L₅ aren't as stable for a "small mass" there starts to approach the mass of the Earth.  For example, in Saturn's moon system, Dione's co-orbital moon at its L₅ point, Polydeuces, is about 1/10⁸ the mass of Dione and it wanders up to 32° from the L₅ point.   Theia would have been more relatively massive than that, about 1/10 the mass of the Earth, and especially with perturbations from Venus and Jupiter would have wandered farther.

Definitions have to be useful.  The current definition for 'plant' is useful.  Pluto isn't a planet.

"Ting!"  Your time for an argument has expired.  Good day!

[kerbiloid]

2 minutes ago, Jacke said:

Earth does have a resonance.  With Venus.  At inferior conjunction, the same side of Venus faces the Earth.  Explain that one.

Why have to explain it in this context?
The Venusian orbit doesn't cross the terrestrial one, while the Proto-Moon / Teia was occupying exactly same orbit, just with 60° offset.

5 minutes ago, Jacke said:

Yes a resonance can be effectively stable for a very long time under the right conditions. 

Then what is "to clear the orbit"?
Let'em all keep orbiting in happy resonance with each other, as they can do it for ages, and consider them all as "planets".

10 minutes ago, Jacke said:

Pluto and Neptune are more than just in a 3:2 resonance.  Because of the eccentricity and relative inclination of Pluto's orbit, the two orbits aren't even close.  And the perturbing effects of Jupiter and Saturn aren't enough to change that.

https://en.wikipedia.org/wiki/Stability_of_the_Solar_System#Neptune–Pluto_resonance

They say, the Neptune-Pluto resonant system is short-term stable, but is not predictable in long-term case.

As the Neptune-Pluto orbits are ~35 AU, and the Earth-(Proto-Moon/Teia) are 1 AU,  thus their orbital paths are 35:1 and their orbital speeds are sqrt(1):sqrt(35) ~= 1:6, so the number of their revolutions is ~200:1 per same time interval.

This means that the same number of close approaches which Neptune-Pluto had for last 4 000  mln years, the Earth-(Proto-Moon/Teia) had faced in their first 20 mln years.

This makes to think that the N-P system is no more stable that the Earth-Proto-Moon was, just is moving slower.

Briefly: the N-P system is more stable in sense of absolute time, but not in sense of orbital revolution count.
Thus, Neptune can't be considered as "having cleared its orbit".

21 minutes ago, Jacke said:

There are 8 planets who have cleared their orbits.  Pluto, like Ceres, is just the largest of a whole class of smaller bodies of similar size to themselves in similar orbits. 

I don't say that Pluto is. I say, that Neptune isn't.

Thus, according to the IAU definition, now we have not 8 but 7 planes, while both Pluto and Neptune are dwarf planets.

22 minutes ago, Jacke said:

Are you referring to yourself in the 3rd person?  Really?

I refer to myself in the 3rd person to continue the @NFUN's phrase from the pov of a 3rd party observer.

24 minutes ago, Jacke said:

Are you talking about Theia?  That's not the Moon. 

I'm talking about the Moon mother body, which some refer to as "Teia".
(Though I find this naming disgusting and morally rotten, as a totally unfair emotional manipulation in form of personification of the object of study, to make others treat it as emotionally familiar and take the authors' theory by default.
The older term "Proto-Moon" is much more neutral and fine, but not everybody understands what's that).

30 minutes ago, Jacke said:

And Earth's Lagrande points L₄ and L₅ aren't as stable for a "small mass" there starts to approach the mass of the Earth.  For example, in Saturn's moon system, Dione's co-orbital moon at its L₅ point, Polydeuces, is about 1/10⁸ the mass of Dione and it wanders up to 32° from the L₅ point.   Theia would have been more relatively massive than that, about 1/10 the mass of the Earth, and especially with perturbations from Venus and Jupiter would have wandered farther.

I mean that the Proto-Moon (which ihad presumably formed at some of Lagrange points) was occupying a resonant orbit, and then approached too close. Thus, a currently existing resonance doesn't mean that the orbit is "cleared", whatever IAU means by this word, as they didn't bother to explain.

[callmecapy]

imo pluto is a planet

[kerbiloid]

"I swear, it is!"

[Superpluto126]

Yes, In my own opinion it absolutely is. There are plenty of Asteroids in Earths Orbit, I don't think any planet besides Mercury has cleared their orbit fully. Its also not up to humans to decide if one object is better than another beyond classification for Moons and Asteroids. Moreover, the commonly known Dwarf Planets have clearly Special Atributes.

 

Also Barring what I just said about Humans not needing to get involved, this is a Much better idea for Planets and Dwarf Planets.

On 2/25/2023 at 9:33 PM, ProtoJeb21 said:

I feel like the term "dwarf planet" needs retooling. Pretty much any spherical object in the Kuiper Belt can be counted as a dwarf planet - gravitationally rounded bodies that haven't fully cleared their orbits - but the truth probably isn't that simple. A 2019 paper (Grundy et al. 2019) on a ~600 km KBO whose name I won't even attempt to try and spell concluded that some KBOs below 900-1000 km in diameter may not be fully differentiated and exhibit internal porosity. If that's the case, then the largest dwarf planets like Pluto, Eris, pre-impact Haumea, Makemake, Quaoar, and Gonggong are massive enough to both collapse into a sphere and have differentiated interiors, while many sub-900 km dwarf planets/KBOs may be rounded but undifferentiated. This may finally be a lower size limit on what can be considered planets and I think should be incorporated into the definitions of planets and dwarf planets. 

I'd argue that internal differentiation is a more important classification criteria than orbital clearing, not just because the definition of latter is vague and arbitrarily excludes pretty much every major planet (asteroids cross their orbits so technically they violate that criteria), but because it isn't really about the properties of the object itself. Rather, it's based on the object in comparison with its surroundings. Internal differentiation is a key characteristic of an object's structure and formation, is easy to understand, and can set a hard lower limit for planets or dwarf planets. I think the best options are to set a dividing line at 900-1000 km, and either make all the dwarf planets above that into major planets, or demote all the dwarf planet candidates below that into their own new category of KBO/SSSO.

As for Pluto, I think there's decent justification for upgrading back to a planet. Even with my suggested internal differentiation criteria, whether Pluto would officially get upgraded to a planet or not depends if the IAU ever does anything about the orbital clearing criteria.

something like this, potentially?

[NFUN]

you managed to throw every fallacy about this whole debate into one paragraph. congrats