Pluto is was and always will be a planet

theprestige said:
There's more than two categories of stars. Why can't there be more than two categories of planets?
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A single member does not a category make.

theprestige said:
And so what if we find more planets in the plutoid category? There's more than one planet in the gas giant category, and you're not pooping your pants over that.
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And there's the thing. There are more objects in the plutoid category. We classify them as Kuiper Belt Objects.
 
Belz... said:
Sounds good to me. When I get older, I'll no longer be middle-aged. I've got no problem with items changing category with time.
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I'm not categorically against the Moon being elevated to planet status, but the mechanism doesn't make much sense. Why should the exact orbital radius of the smaller body determine whether it's a moon or a planet? That doesn't comport with common understanding or historical usage of what "moon" means, and I don't see any important technical reason to introduce that as a distinguishing feature.

If two very similar bodies are orbiting each other, and each individually would qualify as a planet, then it makes sense to call both of them planets together. And in such a scenario, the barycenter will almost certainly lie between them, outside both of their surfaces. But that's not a good way of distinguishing binary planets from planet/moon systems, because the barycenter being outside of both doesn't guarantee any similarity in their masses. It makes more sense to simply determine a cutoff mass ratio (for example, maybe 4-to-1, but it could be anything). Below this ratio, both bodies can be planets, above it and the larger one is a planet while the smaller one is its moon. This comports better with historical usage and common understanding, and the quantity under consideration is more stable over time.
 
Myriad said:
If it's spherical and manmade and directly orbiting the sun it's an artificial planet.
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The requirement for planethood is not that the object be spherical. The requirement is that gravity shape it into a sphere (or more accurately, hydrostatic equilibrium). If it's spherical because you cut and polished it into a sphere, that doesn't count, Oracle be damned.
 
Ziggurat said:
I'm not categorically against the Moon being elevated to planet status, but the mechanism doesn't make much sense. Why should the exact orbital radius of the smaller body determine whether it's a moon or a planet? That doesn't comport with common understanding or historical usage of what "moon" means, and I don't see any important technical reason to introduce that as a distinguishing feature.

If two very similar bodies are orbiting each other, and each individually would qualify as a planet, then it makes sense to call both of them planets together. And in such a scenario, the barycenter will almost certainly lie between them, outside both of their surfaces. But that's not a good way of distinguishing binary planets from planet/moon systems, because the barycenter being outside of both doesn't guarantee any similarity in their masses. It makes more sense to simply determine a cutoff mass ratio (for example, maybe 4-to-1, but it could be anything). Below this ratio, both bodies can be planets, above it and the larger one is a planet while the smaller one is its moon. This comports better with historical usage and common understanding, and the quantity under consideration is more stable over time.
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Makes sense with the mass this way, yes.

But the barycenter makes just as much sense, and although it doesn't guarantee a similarity in mass, mass might not be a criterion at all.

Ziggurat said:
The requirement for planethood is not that the object be spherical. The requirement is that gravity shape it into a sphere (or more accurately, hydrostatic equilibrium).
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That doesn't comport with common understanding or historical usage of what "planet" means. ;)
 
Belz... said:
Makes sense with the mass this way, yes.

But the barycenter makes just as much sense, and although it doesn't guarantee a similarity in mass, mass might not be a criterion at all.
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Barycenter within the planet is much better than clearing the neighborhood since it's at least a clear and easily determined criterion. But I don't think it's actually useful in any way. The dividing line is uninformative. Should the fact that the Sun/Jupiter barycenter is outside the sun change the status of the Sun or Jupiter?

That doesn't comport with common understanding or historical usage of what "planet" means. ;)
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It doesn't comport with the original usage. But historical usage encompasses more than just original usage. :p
 
Ziggurat said:
Barycenter within the planet is much better than clearing the neighborhood since it's at least a clear and easily determined criterion. But I don't think it's actually useful in any way. The dividing line is uninformative.
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I don't see how less informative it is than any other arbitrary criterion. What it informs in this case is the body's relationship with nearby bodies. In a way, it tells you how dominant the body is relative to nearby ones.

Should the fact that the Sun/Jupiter barycenter is outside the sun change the status of the Sun or Jupiter?
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No because the issue of the barycenter doesn't involve stars, only planets. A much more important issue is the Earth-Jupier barycenter. But then no one would claim that the two orbit one another.
 
arthwollipot said:
A single member does not a category make.
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That may be true. It's certainly irrelevant: The IAU already puts Pluto, Ceres, Sedna, and Eris in the same category.

And there's the thing. There are more objects in the plutoid category. We classify them as Kuiper Belt Objects.
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Some KBOs are, like Pluto, "dwarf planets" under the IAU's current definition. Others are not. The argument under discussion is whether objects that meet the current "dwarf planet" definition should be considered a subcategory of planet.

That doesn't mean we have to consider every KBO a planet of some kind. Though we can if we want, obviously.
 
Belz... said:
I don't see how less informative it is than any other arbitrary criterion. What it informs in this case is the body's relationship with nearby bodies. In a way, it tells you how dominant the body is relative to nearby ones.
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But it doesn't. The earth isn't going to be any less dominant when the earth-moon barycenter is outside of earth than it is now.

No because the issue of the barycenter doesn't involve stars, only planets.
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That's by arbitrary choice though. If the barycenter being outside the larger body has any intrinsic meaning, then it has that meaning regardless of whether it's a planet or a star. But it doesn't have any intrinsic meaning. It has a correlation with some other things which are of interest (namely the ratio of masses of the objects), but because of its strong dependence on other factors, it's a very poor proxy for that other thing of interest, which you're much better off measuring directly.
 
Ziggurat said:
But it doesn't. The earth isn't going to be any less dominant when the earth-moon barycenter is outside of earth than it is now.
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Depends what you mean. The Moon being farther, it'll be less affected by the earth's gravity. Doesn't that affect the Earth's dominance?

That's by arbitrary choice though. If the barycenter being outside the larger body has any intrinsic meaning, then it has that meaning regardless of whether it's a planet or a star. But it doesn't have any intrinsic meaning.
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Nothing has intrinsic meaning, Zig. That's not the point of a category.
 
This thing needs to go to a Poll. A no holds barred, put up or shut up, winner take the internet Poll!


Mods, make it happen. I want every news agency's lead story to be "The International Skeptics Forum" has determined that Pluto is ...

to be continued.
 
angrysoba said:
I think theprestige's point was that there was never any need to change Pluto from planet to dwarf planet. All the reasons given for doing so are specious.
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Other than consistent definitions. There was also no need to change Ceres from being a planet either.
 
Elagabalus said:
This thing needs to go to a Poll. A no holds barred, put up or shut up, winner take the internet Poll!


Mods, make it happen. I want every news agency's lead story to be "The International Skeptics Forum" has determined that Pluto is ...

to be continued.
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Democratisation of science. I love it!
 
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