So Pluto is a planet!?

[N_las]

So do you agree the IAU's definition of a planet was just an exercise in shoehorning in a definition that fits a group of objects?

The important thing in the IAU's definition is classifying the objects in our solar system. We clearly have a class of 8 main bodys (that can be further divided) and other classes of objects. This classification isn't shoehorning at all. The 8 main objects are the objects that are gravitationally significant in their respective orbits. The fact that pluto isn't in the same class than the 8 main objects is indisputable.

The NAMES are shoehorning. But names are always shoehorning. The naming scheme that has the best overlap with traditional naming schemes is naming the 8 main objects "planets". That is rather arbitrary, but it is just a name. Even if we would use the name "planet" for every round thing in space, we would than invent a name like "REAL planet" or "PROPER planet" or "not-pluto-like planet" to describe the 8 main objects. That wouldn't change the fact that pluto isn't allowed in the club anymore.

Do you include Mercury in that?

Yes, because Mercury is dominant in his part of the solar system. Pluto on the other hand is insignificant in his part of the solar system.

Incidentally, other scientific disciplines aren't exactly embracing the definition. Certainly geologists and geophysicists don't feel compelled to pay the slightest bit of attention to it.

And cosmologist are calling everything heavier than helium a "metal". I am pretty sure that geologists are considering cosmologist opinions the next time they dig up a piece of "metal" and want to distinguish it from the other piece of "metal". Imagine their would be a discussion if Oxygen should be considered a "metal". It is the same with "pluto as planet". From a geologists point of few it may look like a planet, but who cares?

What do you mean by that? Are you calling me and the geophysical word a "whiney little ....." just because we think the IAU are in error with their definition?

Yes.

Edited October 6, 2014 by N_las

[ZetaX]

I would like to see that geologist definition of a planet.

[Kryten]

Geology working with bodies other than earth is a subset of planetary science, and the planetary science definition is basically 'anything smaller than a star'.

[Camacha]

I would prefer to have this conversation without people calling each other whiny or use other ad hominems. Could we please do that?

For one thing, because the gravitational influence of all the stuff except the planets (and the Sun) is negligible. The 8 planets (and the Sun) are the objects that dominate the orbital mechanics of our solar system. Everything else is just debris.

You prove the point beautifully. If you look at the gravitational influence of everything outside the sun it is negligible. Drawing the line after the heaviest (not even the biggest) eight seems an exercise to make the definition fit a certain view rather than looking at the bodies we know and coming up with a proper and useful segmented definition. Not how science should go about its business, if you ask me.

I could not care less about the Pluto status. It is what that signifies.

The important thing in the IAU's definition is classifying the objects in our solar system. We clearly have a class of 8 main bodys (that can be further divided) and other classes of objects. This classification isn't shoehorning at all. The 8 main objects are the objects that are gravitationally significant in their respective orbits. The fact that pluto isn't in the same class than the 8 main objects is indisputable.

We can wriggle definitions around any group or class we want to exist. The difference between Mercury and Jupiter by most standards is bigger than that between Mars and Ceres. That means that your suggestion that it is in fact an objective definition becomes rather shaky. I just depends on how you look at the facts and as by magic the current definition fits our historic view on things. Doesn't that make you wonder?

[ZetaX]

We can wriggle definitions around any group or class we want to exist. The difference between Mercury and Jupiter by most standards is bigger than that between Mars and Ceres.

Your only standard seems to be some variations on "how it looks like"¿

That means that your suggestion that it is in fact an objective definition becomes rather shaky.

The definition is pretty objective. A definition being objective has nothing to do with agreement or matching your version. The definition "a sphere is a round thing" is subjective, "a sphere is an object of constant curvature" is objective. You could now argue that a flat plane is no sphere, but that's only so because you project your expectation into it and/or because there is another possible definition. The given definition itself is still objective.

[N_las]

We can wriggle definitions around any group or class we want to exist. The difference between Mercury and Jupiter by most standards is bigger than that between Mars and Ceres. That means that your suggestion that it is in fact an objective definition becomes rather shaky.

I don't see how Mars and Ceres are alike. But I can see how Mercury and Jupiter are alike.

Mercury, Mars and Jupiter scooped up nearly everthying in their part of the solar system. That is the important bit. The fact that Jupiter scooped up much gas, and is able to hold it, doesn't differentiate it. If we have several vacuum cleaners, and I use mine to scoop dirt, and you use yours to scoop water, they are both still vacuum cleaners.

Ceres on the other hand hasn't played a gravitational role in its part of the solar system at all. It isn't like a vacuum cleaner. It is more like a dung beetle. If you compare the scooped materials, you may say that the dung beetle is the same than a vacuum cleaner, because they may have picked up the same kind of dirt. But lets be real here. If you aren't interested in the KIND of dirt your vacuum cleaner is scooping up, but your are interested in a clean kitchen, then vacuum cleaners are clearly different from dung beetles.

I just depends on how you look at the facts and as by magic the current definition fits our historic view on things. Doesn't that make you wonder?

You have it exactly backwards. If it isn't the DEFINITON that is influenced by historic views. If the definition was influenced by historic views, than we WOULD call Pluto a planet. It is the opposite, the definition is influenced by our current understandig of the world. Only the NAMES are influenced by history.

It isn't that we pick a name, say 'apples' or 'planets', and they we define which objects are encompassed by which group-name. We define certain criteria that allow us to sort objects in different categories, based on usefulness. These definitions are independent of their name. We just name the categories in a manner that causes the least confusion (to increase usefulness).

It may be useful for geologists to call every rock-thingy in space a "Planet". But that is why I used the "metal" example in my previous post. It is also useful for cosmologist to call everything heavier than Helium a "metal". If you wan't to be precise about elements, then you don't talk to a cosmologist, but a chemist or something. If you want to be precise about astronomical object you talk to an astronomer, not an geologist.

Edited October 6, 2014 by N_las

[Albert VDS]

Planet is a very old word that was given to things that were nothing more than points of light that moved against the background of stars. To try and find a retrospective scientific definition based on what we have since learnt about them that only includes those objects seems pointless and foolhardy.

Why is that such a problem, every language is full of words which originally mean something else.

Just look up some random words on dictionary.com and you'll see that it's original meaning has nothing to do with what it means now.

[ZetaX]

Anyone why claims that "planet" was redefined to fit that ancient definition probably also does not know that there is no way Neptune was observed before the invention of telescopes. Ceres is 1.5 magnitudes brighter than Neptune, each under optimal conditions.

[Fingal]

ITT, random people on the Internet think that they know better than the professionals that invest their lives in the study of the solar system.

Are you including professional geophysicists and geologists as "random people on the internet"?

[Fingal]

Why is that such a problem, every language is full of words which originally mean something else.

Just look up some random words on dictionary.com and you'll see that it's original meaning has nothing to do with what it means now.

I couldn't agree more, which is why I don't understand the need to produce a contorted definition that conforms to the historic use.

- - - Updated - - -

Anyone why claims that "planet" was redefined to fit that ancient definition probably also does not know that there is no way Neptune was observed before the invention of telescopes. Ceres is 1.5 magnitudes brighter than Neptune, each under optimal conditions.

No, I'm familiar with the history of astronomy.

[ZetaX]

I think N_las now better understands my problems in a certain other thread

I couldn't agree more, which is why I don't understand the need to produce a contorted definition that conforms to the historic use.

No, I'm familiar with the history of astronomy.

Obviously not if you think that neptune is a historical planet.

[KerikBalm]

Pluto is clearly different from the other 8.

The other 8 were not all known when people first started speaking of planets.

What was known of the planets in historic times comes down to their orbital properties - they'd move about the sky, unlike the "fixed" stars

Yet those of the 8 that were not known in history clearly are of the same orbital class at the ones that were known.

The definition we have now is objective.

It forms a natural group as there is a huge separation in the parameters.

They found a natural group that also conforms to the old usage of it. Or at least one of the old usages. The less old usage, what had become "quasi traditional", which regarded pluto as a planet, had to be done away with, because it was an unnatural grouping.

Unless you want to promote Ceres to Dwarf planet and a dozen other bodies, you've got no objective standard, and one might still dispute that its a natural group (why ceres but not vesta!?)

[Fingal]

Unless you want to promote Ceres to Dwarf planet and a dozen other bodies, you've got no objective standard, and one might still dispute that its a natural group (why ceres but not vesta!?)

I'd very much like to promote Ceres and any other body that doesn't support fusion and has achieved hydrostatic equilibrium. The idea that it's all about Pluto is a strawman designed to make people look emotional or irrational.

[N_las]

The exact same discussion could have been made 150 years ago with the asteroids. But everyone agreed that we should differentiate asteroids from planets. No we have asteroids like pluto in the kupier belt. Why the fuss? What is different from 150 years ago? Nothing. The only thing different is, that thanks to the internet, a lot of people who don't have much to do with astronomy can loudly proclaim their opinions.

Of course, like in every academic disussion, some astronomers have a different opinion about the classification. But those were insignificant fringe opinions 150 years ago, and the same is true for today.

EDIT: Or course, I am also just a guy on the internet, proclaiming my opinion.

Edited October 6, 2014 by Vanamonde
Quoting of argument snipped.

[BagelRabbit]

I just want to come in and say that calling Pluto, Ceres, Eris, etc. "Dwarf Planets" isn't the best terminology. Dwarf stars and dwarf galaxies are still considered stars and galaxies, respectively, yet dwarf planets aren't planets. I understand that the little guys really shouldn't be considered planets, but surely there's a better designation for them. "Minor Planets" maybe? Or "Special Planets?"

...then again, the term "Asteroid" means 'starlike,' and asteroids are as far from being stars as it gets. The only reason that they were called asteroids is that they initially couldn't be resolved, and looked like starlike points. I personally think that they need to be renamed too.

I don't mind Pluto not being considered a planet, as the science behind it is sound, and if it was considered a planet, several dozen other objects would also be considered planets... but I do think that there needs to be a different naming scheme for solar-system objects.

[Fingal]

Of course, like in every academic disussion, some astronomers have a different opinion about the classification. But those were insignificant fringe opinions 150 years ago, and the same is true for today.

Again you exclude the entire geophysics and geology field, a group who probably spend more time studying planets & moons than astronomers. I think they're a little more than just "insignificant fringe opinions".

[m4v]

Are you including professional geophysicists and geologists as "random people on the internet"?

who? give some names, citations, something, you're making a vague and generic statement and making out to be that most geophysicist and geologists disagree with the definition, if that's true then the IAU wouldn't have approved it with a near unanimous vote.

Edited October 6, 2014 by Vanamonde
Let's not get into national characters, please.

[Fingal]

who? give some names, citations, something, you're making a vague and generic statement and making out to be that most geophysicist and geologists disagree with the definition, if that's true then the IAU wouldn't have approved it with a near unanimous vote.

Ten seconds on google can give you all the information you need. And a vote that involves the membership of around 5% of the eligible voters, unanimous or not, is not what I'd call credible.

Edited October 6, 2014 by Vanamonde
Quote of argument removed.

[Kryten]

Ten seconds on google can give you all the information you need.

There is no geographical definition of a planet, they work with 'planetary bodies'. If you want to conflate the two, you've now got meteoroids and moons as planets.

[Fingal]

There is no geographical definition of a planet, they work with 'planetary bodies'.

There was no astronomical one before 2006 either.

If you want to conflate the two, you've now got meteoroids and moons as planets.

I'm fine with moons being described as planets, but meteoroids tend not to achieve hydrostatic equilibrium.

[N_las]

There is no geographical definition of a planet, they work with 'planetary bodies'. If you want to conflate the two, you've now got meteoroids and moons as planets.

You probably didn't meant "geographical" definition

[Kryten]

I'm fine with moons being described as planets, but meteoroids tend not to achieve hydrostatic equilibrium.

How is that any more relevant to the original definition you were banging on about than clearing the neighbourhood? A meteoroid is as much a moving body as one of the traditional planets.

[Fingal]

How is that any more relevant to the original definition you were banging on about than clearing the neighbourhood? A meteoroid is as much a moving body as one of the traditional planets.

Ask anyone, from a child to a physics professor, to draw you a planet and they'll start by drawing a circle. It's the one thing everyone can agree on. And I'm not advocating a return to it's original meaning, merely pointing out it is an old word that has never been scientifically defined, therefore an attempt to design a definition that applies only to those objects that have been previously called planets is unlikely to be either scientific or sensible.

[LLlAMnYP]

We can wriggle definitions around any group or class we want to exist. The difference between Mercury and Jupiter by most standards is bigger than that between Mars and Ceres. That means that your suggestion that it is in fact an objective definition becomes rather shaky. I just depends on how you look at the facts and as by magic the current definition fits our historic view on things. Doesn't that make you wonder?

By what standards exactly? Soter's planetary discriminant says that the difference between Mercury and Jupiter is a factor of 7. The difference between Mars and Ceres is a factor of 500000. According to the Stern-Levison parameter, the difference between Mercury and Jupiter is about the same as between Mars and Ceres.

In terms of "clearing the neighbourhood" the 8 planets are clearly within one league. In terms of scattering power there's a big gap clearly separating dwarf planets and the big eight, although it is true that the big eight are quite widely spread out themselves.

Edited October 6, 2014 by LLlAMnYP
typos

[m4v]

Ten seconds on google can give you all the information you need. And a vote that involves the membership of around 5% of the eligible voters, unanimous or not, is not what I'd call credible.

You're the one with the space teapot, you source your claims. And if they didn't participate in the vote then tough luck, the right time to make your opinion count are during the general assemblies, not after.

But lets imagine that the 100% of the members did vote, you think that the result would have been different? in statistics a 5% percent sample is pretty much good enough for infer anything about the total population with good confidence, the vote was almost unanimous, whoever is complaining is just a vocal minority.

Edited October 6, 2014 by m4v