Pluto is was and always will be a planet

[Belz...]

A planet should orbit the sun and not some larger planet (ie, Titan is a moon and not a planet), and it should be large enough to gravitationally shape itself into hydrostatic equilibrium.

Do you think we should define this orbit in terms of barycenter? I ask because Pluto-Charon's is outside either bodies, as is Sun-Jupiter's. How about binary star systems? Or do we just stick to this system for now?

I'm open to arguments to narrow this down a little more, perhaps with a mass or diameter threshold

Gravity and orbital eccentricity, perhaps.

but clearing your neighborhood is a bad criteria.

I personally dislike it. I don't find that it's particularily well-defined, to begin with. Jupiter has 'cleared' its neighborhood but there's a ton of small bodies along its orbit.

For another, that criteria means that planets can potentially lose and gain planetary status multiple times even with no change to their own properties. That seems ridiculous.

That doesn't bother me. If a planet is blown apart by a collision, it loses its status as planet because it no longer exists, and gains it back if it coalesces again.

Because the definition shouldn't be history-dependent.

Why not? I'm being serious. Why shouldn't it be?

That is very, very unlikely. It is highly probable we haven't found every dwarf planet in our solar system, but if there are thousands of dwarf planets, then there are going to be a much larger number of things that aren't quite dwarf planets but are still pretty large. And we should be seeing a lot more of them than we are.

Most of them are at a distance comparable to Sedna and beyond and are very small and dim. Odds are that just haven't been looking in the right places. It may just be a few hundreds but maybe more, given the size of the system, and I don't want kids in the classrooms to have to memorise more than those we decide to call planet.

 

[Ziggurat]

Do you think we should define this orbit in terms of barycenter? I ask because Pluto-Charon's is outside either bodies, as is Sun-Jupiter's.

What difference does that make?

If you're suggesting that Pluto shouldn't be a planet because the Pluto/Charon barycenter is outside Pluto, I disagree. That will happen to the Earth/Moon system in the future too, and that shouldn't demote the earth. If you're just noting that Jupiter orbits the barycenter of Jupiter/Sun and not the center of the sun, sure, but it still goes around the sun and not around another larger planet.

How about binary star systems?

I don't think that changes anything. The object with either orbit one sun (orbital distance less than the distance between the two suns) or it will orbit both suns (orbital distance greater than the distance between the two suns). In either case, it will still be either orbiting a sun or suns, or it will be orbiting some larger body which the will both orbit the sun(s) together. In the former case it may be a planet, in the latter case it's a moon.

Gravity and orbital eccentricity, perhaps.

Gravity is essentially equivalent to mass. Not identical, but sufficiently related that one or the other would serve essentially the same purpose. I don't think orbital eccentricity needs to be a criteria. Imagine, for example, a Jupiter-like planet orbiting another star on a very elliptical orbit. Should it not be considered a planet because its orbit is elliptical? That doesn't seem right.

I personally dislike it.

That's the criteria used to boot Pluto.

That doesn't bother me. If a planet is blown apart by a collision, it loses its status as planet because it no longer exists, and gains it back if it coalesces again.

A planet that gets blown apart should lose its status because it's no longer gravitationally formed into hydrostatic equilibrium, so that's not the problem. The problem is that other planets can lose their status because a neighbor was blown apart by a collision. Nothing about those other planets needs to change for their status to change, under that definition.

Why not? I'm being serious. Why shouldn't it be?

Because we should be able to determine its status as a planet or not planet based upon its current properties. We shouldn't have to discover the history of its creation to know this.

Most of them are at a distance comparable to Sedna and beyond and are very small and dim. Odds are that just haven't been looking in the right places. It may just be a few hundreds but maybe more, given the size of the system

The farther out you go, the harder it is for large bodies to form. There is less and less material available, it's more and more dispersed, and it takes longer and longer for that material to coalesce.

and I don't want kids in the classrooms to have to memorise more than those we decide to call planet.

I'm OK with kids not memorizing everything in our solar system we call a planet. In general, kids already don't memorize any of the names stars other than the Sun, and I bet most kids couldn't name a galaxy other than the Milky Way.

 

[Ziggurat]

Nobody's saying Pluto and Ceres and Eris and all them were never considered planets, just that they aren't planets under the definition we are using now.

We can say the Greeks used to consider the Sun and Moon planets under their definition but we don't know, why is this any different?

Did you not read my previous post? I wasn't referring to the history of the word. I was referring to the history of the object, as in, how and where did the object form, how did it arrive at its current location. The Greeks don't have anything to do with that. Past word usage doesn't have anything to do with that.

 

[Belz...]

What difference does that make?

I'm just throwing ideas out there. Definitions are arbitrary, so I'm wondering why we would pick one criterion and not the other.

That will happen to the Earth/Moon system in the future too, and that shouldn't demote the earth.

Again with the value judgments. Do you have a relationship with Pluto that we should know about?

I don't think orbital eccentricity needs to be a criteria. Imagine, for example, a Jupiter-like planet orbiting another star on a very elliptical orbit. Should it not be considered a planet because its orbit is elliptical? That doesn't seem right.

What does the highlighted even mean?

That's the criteria used to boot Pluto.

I know. I was agreeing with you.

A planet that gets blown apart should lose its status because it's no longer gravitationally formed into hydrostatic equilibrium, so that's not the problem. The problem is that other planets can lose their status because a neighbor was blown apart by a collision. Nothing about those other planets needs to change for their status to change, under that definition.

Yeah, but that's because of your personal definition of planet. Regardless of definition, a planet's status would change if it fails even temporarily to meet the requirements.

Because we should be able to determine its status as a planet or not planet based upon its current properties. We shouldn't have to discover the history of its creation to know this.

You keep using "shouldn't" as if it's convincing on its face. I want you to provide me with reasons that don't amoung to your personal like or dislike.

The farther out you go, the harder it is for large bodies to form. There is less and less material available, it's more and more dispersed, and it takes longer and longer for that material to coalesce.

That might be true, but doesn't rule out a few hundred dwarf planets. The solar system's huge, and has quite a lot of material.

 

[Ziggurat]

Yeah, but that's because of your personal definition of planet.

No, that's because of the IAU definition.

Regardless of definition, a planet's status would change if it fails even temporarily to meet the requirements.

Sure, but the issue is what sort of changes would make this happen. Changes which don't directly affect the planet itself should not change its status.

You keep using "shouldn't" as if it's convincing on its face. I want you to provide me with reasons that don't amoung to your personal like or dislike.

Any evaluation of competing possibilities will always come down to some value judgment. Preferring fewer criteria to more criteria is a value judgment. Preferring simpler criteria to more complex criteria is a value judgment. Preferring criteria that are easy to evaluate over criteria that are hard to evaluate is a value judgment Preferring criteria which keep classifications stable over criteria which lead to fluid classifications is a value judgment. And any value judgment can always be framed as a personal like or dislike. I don't see how I can satisfy your request, for any possible criteria.

 

[jeremyp]

The Solar System:

- 1 Teapot (Status contested)

Pretty sure there’s more than one teapot in the solar system. In fact, I can see two from where I’m sitting.

Maybe Elon Musk could have put one on that rocket instead of a Tesla Roadster. That would put a spanner in the works for the atheists.

 

[jeremyp]

I’m still bitter about the quiz night for charity I attended at my nephew’s school which had the question “name all the planets in the solar system”. The official “question master is always right” answer had eight planets, including Pluto but not including Venus.

 

[JoeMorgue]

I’m still bitter about the quiz night for charity I attended at my nephew’s school which had the question “name all the planets in the solar system”. The official “question master is always right” answer had eight planets, including Pluto but not including Venus.

Technically Venus is an arachnid.

 

[Skeptic Ginger]

I always thought 'big enough to pull itself into a sphere' was the best and most obvious definition...

So the Moon is really a planet?

 

[Giordano]

I am not an astronomer in any way. However I do have a PhD. So with all the vast authority granted to me as a consequence of those extra 5 years of avoiding a real job I hereby grant to all posters here the right to call Pluto a planet if they wish to so. Neil deGrasse Tyson is unlikely to overhear you, even highly drunk customers in Biker Bars are unlikely to punch you for it, and at some time you will give a 9-year kid intense pleasure "correcting" you.

Did you know that not drawing pants on Pluto was okay because he did not speak and was presented as a dog/pet, whereas drawing pants on Goofy was considered crucial for decorum because he speaks in the cartoons and therefore was human-enough to need clothes. Presumably Goofy's ancestors ate of the fruit of knowledge in Eden; Pluto's did not.

 

[Elagabalus]

...But we aren't only talking about what the definition is. Nor is there any requirement that we all adopt the same definition as the IAU, which has no authority to impose its definition on anyone ...

I hope you know what you're doing, Zig. The IAU is not to be trifled with. There are more things that can be done with sweater vests, pocket protectors and inappropriately sexist comic book themed self printed T-shirts than just wearing them as a de rigueur nerdist fashion statement!

You have been warned!

 

[Belz...]

No, that's because of the IAU definition.

"Nothing about those other planets needs to change for their status to change, under that definition." has to be under your definition, since you say that under the IAU definition the status can change.

Sure, but the issue is what sort of changes would make this happen. Changes which don't directly affect the planet itself should not change its status.

Sorry, but by definition all criteria that are part of the definition of planet affect the planet itself. Otherwise by what would you determine if it affects the planet or not?

Any evaluation of competing possibilities will always come down to some value judgment.

Maybe but there's arbitrary and then there's arbitrary. If you choose a definition based on a number of criteria because they allow you to categorise bodies in a way that's useful for a number of purposes, that's fine. But so far your arguments can be summed up like this:

That doesn't seem right.

But yes, you can satisfy my request. All you have to do is make a case as to why your definition would be more useful, or why the current one is problematic in a way not easily addressed.

 

[Faydra]

I can't get out of the sand metaphor.

I imagine Jupiter coming along and kicking the Universe's sand in Pluto's face and then Pluto desperately trying to kick the sand back out of it's own orbit and just continually getting sand back in it's own non-planety face.

It's making me laugh way too much, and I haven't even smoked any pot in like a month!

 

[gerdbonk]

Pluto smokes pot. Look at that orbit.

 

[Ziggurat]

"Nothing about those other planets needs to change for their status to change, under that definition." has to be under your definition, since you say that under the IAU definition the status can change.

You're misinterpreting something, and I'm not sure what, so let me lay it out more explicitly in one place.

If we use the IAU definition of planet (not mine), then if Mars blows up and throws debris into Earth's neighborhood, Earth gets demoted from planet to dwarf planet. Nothing about Earth itself, the physical object, changed, but its classification does, under the IAU definition.

Sorry, but by definition all criteria that are part of the definition of planet affect the planet itself. Otherwise by what would you determine if it affects the planet or not?

That's backwards. Things affect objects independently of how we classify objects.

If you add or subtract mass to Earth, that affects Earth directly. If you put Earth in orbit around Jupiter, that affects Earth directly. If you blow up Mars, that does not affect Earth directly. None of this is dependent upon the definition of the word "planet". It's a simple examination of physical interactions.

Maybe but there's arbitrary and then there's arbitrary. If you choose a definition based on a number of criteria because they allow you to categorise bodies in a way that's useful for a number of purposes, that's fine. But so far your arguments can be summed up like this:



But yes, you can satisfy my request. All you have to do is make a case as to why your definition would be more useful, or why the current one is problematic in a way not easily addressed.

We've already done that. You even agreed with me that clearing the neighborhood is a bad criteria. It's hard to evaluate, and it's not even a useful distinguisher between different astronomical bodies. In the hypothetical where Mars blows up and scatters debris, that could lead to Jupiter being demoted to dwarf planet status. So that criteria is garbage, because it makes no sense to have Jupiter be a dwarf planet while Mercury is a planet. That violates the entire purpose of separating dwarf planets from planets in the first place..

So why not simply throw out that criteria? Maintain the other criteria (orbiting the sun, not a bigger planet, gravitationally shaped into hydrostatic equilibrium), because they work perfectly well, and you're fine. It's simpler, it's easier to evaluate, and it doesn't lead to absurd possibilities like Jupiter being a dwarf planet.

The primary objection on offer is that it leads to too many planets, but no case has been made for why that's actually a problem. You suggested (but didn't actually advocate for) another criteria, a limit to how elliptical an orbit should be, but that criteria is as arbitrary as it gets, and serves no purpose except to exclude certain candidates because... well, we never got that far. And again, it would lead to Jupiter-like extrasolar planets being classified as dwarf planets, which makes zero sense.

 

[Steve]

It's my theory that the Solar System has little planets on the inside, big ones in the middle, and little ones on the outside.

That is my theory, it is mine and belongs to me, and I own it and what it is, too.

Also, it looks like a Brontosaurus.

Ann? Is that you? It's been a looooong time!

 

[Red Baron Farms]

So Ceres is a planet too?

yes

 

[Belz...]

You're misinterpreting something, and I'm not sure what, so let me lay it out more explicitly in one place.

If we use the IAU definition of planet (not mine), then if Mars blows up and throws debris into Earth's neighborhood, Earth gets demoted from planet to dwarf planet. Nothing about Earth itself, the physical object, changed, but its classification does, under the IAU definition.

Yes I get that. What I'm saying is that when you say it shouldn't work that way, it's based on your definition, but you've not provided a reason why it shouldn't work that way,

That's backwards. Things affect objects independently of how we classify objects.

That's not what I said. Consider: Is an egg still an egg once I break it open and empty it of its contents?

We've already done that. You even agreed with me that clearing the neighborhood is a bad criteria.

That's not the same as agreeing with YOUR definition.

So why not simply throw out that criteria? Maintain the other criteria (orbiting the sun, not a bigger planet, gravitationally shaped into hydrostatic equilibrium), because they work perfectly well, and you're fine. It's simpler, it's easier to evaluate, and it doesn't lead to absurd possibilities like Jupiter being a dwarf planet.

However we end up with a large number of planets, which is what the change was meant to address. You say it's not a problem, but it becomes a problem of classification. Sure, if you call Sedna "Sol 17" instead, you have no problem. But some of us want to be able to have a clear definition of what's a planet that doesn't necessarily include the icy, largely irrelevant bodies that lie in the kuiper belt.

 

[angrysoba]

But some of us want to be able to have a clear definition of what's a planet that doesn't necessarily include the icy, largely irrelevant bodies that lie in the kuiper belt.

I don’t get what “relevance” has to do with it. This surely depends on what we consider relevant at any one time. We have probes visiting Ceres and Pluto and even landed one on a comet, so they have some relevance to someone. We could argued that really only Jupiter has much relevance to Earth by its apparent sweeping up of Earth-bound meteors.

Besides, if we are talking about planets we can see in the sky or of a certain size then the exoplanets would not be relevant either. Apparently the definition of planet only relates to bodies in the solar system which seems a strange definition. Maybe we could just divide them into major planets (of which there are eight according to IUA rules) and the others can be dwarf planets and together they are all planets.

 

[Ziggurat]

Yes I get that. What I'm saying is that when you say it shouldn't work that way, it's based on your definition, but you've not provided a reason why it shouldn't work that way,

At a certain point, this stuff should be obvious. A dwarf planet should be something too small to be a real planet. A definition of dwarf planet that includes Jupiter is a bad definition, because it's misleading.

That's not what I said. Consider: Is an egg still an egg once I break it open and empty it of its contents?

No, it isn't. An egg shell is not an egg.

That's not the same as agreeing with YOUR definition.

Sure, but you've offered neither objection nor alternative.

However we end up with a large number of planets, which is what the change was meant to address. You say it's not a problem, but it becomes a problem of classification.

No, it's not a problem of classification. It's not a problem at all. You keep saying that my preferences are arbitrary, but so is the preference for a smaller number of planets.

Sure, if you call Sedna "Sol 17" instead, you have no problem. But some of us want to be able to have a clear definition of what's a planet that doesn't necessarily include the icy, largely irrelevant bodies that lie in the kuiper belt.

And why does your personal preference matter? Furthermore, I've already suggested multiple better ways to eliminate those smaller objects from the definition.