Pluto is was and always will be a planet

TragicMonkey said:
Root beer barrels have been banned by international treaty as an illegal weapon; tongue-cutting is against the rules of war.
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Damn, that's too bad.
And it's the warm gush of salty blood that really sets off the spicy tang of the root beer.
Oh well. :(
 
TragicMonkey said:
Ruling a line between every object that is a planet and every object that isn't a planet and deciding once and for all which side Pluto falls on achieves nothing. It won't help in understanding Pluto--in fact it'll be detrimental because it'll then be easier to gloss over the contradictions between Pluto's reality and whichever descriptive label we slap it with.
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I'm not sure this is a worthwhile concern. Enthusiasts of planetology, whether by hobby or profession, won't be confused at all by the label. And for the rest of us? So what if we have incorrect assumptions about Pluto?

My cousin managed to reach adulthood under the impression that the sun and the moon the same size. That's bad astronomy, but turns out it's completely irrelevant to her huge success professionally and socially. Do we actually need to worry if she has an accurate understanding of a planet she'll never see and doesn't care about?

Same deal with the flat Earth. Very few people actually need to know that the Earth is round, in any meaningful way. For the vast majority of us, that knowledge changes literally nothing.

I'm all for avoiding doctrinaire adherence to arbitrary labels, but so what if people who don't care about Pluto don't have a good understanding of Pluto?
 
theprestige said:
I'm not sure this is a worthwhile concern. Enthusiasts of planetology, whether by hobby or profession, won't be confused at all by the label. And for the rest of us? So what if we have incorrect assumptions about Pluto?

My cousin managed to reach adulthood under the impression that the sun and the moon the same size. That's bad astronomy, but turns out it's completely irrelevant to her huge success professionally and socially. Do we actually need to worry if she has an accurate understanding of a planet she'll never see and doesn't care about?

Same deal with the flat Earth. Very few people actually need to know that the Earth is round, in any meaningful way. For the vast majority of us, that knowledge changes literally nothing.

I'm all for avoiding doctrinaire adherence to arbitrary labels, but so what if people who don't care about Pluto don't have a good understanding of Pluto?
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People who don't care about a thing wouldn't be interested in it anyway, so why bother considering what they (don't) think about it?
 
Regarding the following definition:

A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
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...here is Steven Novella's suggestion:

Here is my humble suggestion. We keep criteria “a” and “b” and drop “c”. However, we add that the object must not be in a subservient orbit around a larger object. What does that mean? If two objects, like the Earth and Moon, are in orbit around each other, and the center or gravity (barycenter) lies beneath the surface of one of the bodies, then the smaller object will be said to orbit the larger object, and is a moon. Therefore Europa, which is large enough by itself to be a planet, would instead be considered a moon because it orbits Jupiter.

Here is an interesting implication of this – the barycenter between Pluto and Charon (its largest “moon”) lies outside of either body. Therefore, by this definition neither would be a moon, and Pluto-Charon would be a double planetary system – they would both be planets.

Ceres, Eris, and Makemake would be promoted to planets. Haumea is arguably not spherical enough to be a planet, and would remain a dwarf planet. All other confirmed spherical objects would be moons. This means we would go from 8 to 13 planets (the current 8 plus Pluto, Charon, Ceres, Eris, and Makemake). This number is almost sure to grow and more Kuiper belt objects are confirmed.
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Link

Again, it works for me...

Thoughts?
 
sphenisc said:
Haumea is thought to be in hydrostatic equilibrium.
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Yeah, on his podcast, he seemed to have changed his definition somewhat to argue for a roughly spherical shape by some (yes, arbitrary) mathematical formula. Actually, I now wonder about it as it seems to be determined to retain a dwarf planet status without making dwarf planets a subcategory of planet. I think a better solution is just to either abolish dwarf planet as a category, or to just have it as a subcategory of planet.
 
angrysoba said:
Thoughts?
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If Charon gets promoted to planet status because the Pluto/Charon barycenter is outside the surface of Pluto, then our moon will get promoted to a planet in the future. While the earth-moon barycenter is currently below the surface of the earth, that will change eventually as the moon's orbit expands.
 
angrysoba said:
Regarding the following definition:



...here is Steven Novella's suggestion:



Link

Again, it works for me...

Thoughts?
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We need to avoid even numbers and unlucky numbers. Why is everyone hung up on the barycenter thing? If the barycenter is closer to planet X then the circle gets the square.
 
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Ziggurat said:
If Charon gets promoted to planet status because the Pluto/Charon barycenter is outside the surface of Pluto, then our moon will get promoted to a planet in the future. While the earth-moon barycenter is currently below the surface of the earth, that will change eventually as the moon's orbit expands.
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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.
 
Because our moon's orbit is elliptical, the will be a period - I guess millions of years - when the earth-moon barycentre is sometimes within the earth and sometimes outside. So with you new definition the moon would swap back and forth many millions of times between being a moon and a planet.
 
A body is a planet if

a) it is in orbit around the system's star(s), AND is spherical, AND is not orbiting some other body more massive than itself besides the parent star(s)

OR

b) it is inhabited by a species of humanoid aliens whose entire culture can be fully described in a single short phrase, or who have attractive scantily clad blue- or green-skinned women

OR

c) it appears on the "Our Solar System" poster that was hanging on my bedroom wall when I was nine, and isn't a moon, The Sun or The Asteroid Belt

I know there's going to be some debate about this, because of course "attractive" is subjective, but it covers more of the essential distinctions better than any of the other definitions offered in this thread.
 
Myriad said:
A body is a planet if

a) it is in orbit around the system's star(s), AND is spherical, AND is not orbiting some other body more massive than itself besides the parent star(s)
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If we put a spherical probe into orbit around the sun it becomes a planet?
 
TragicMonkey said:
If we put a spherical probe into orbit around the sun it becomes a planet?
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Spherical is exactly the wrong shape for a probe. Probes should be long and probulous. If it's spherical and manmade and directly orbiting the sun it's an artificial planet.

Especially if it also has attractive human-looking alien women on it, and an all-knowing Oracle that's actually a computer that roasts you alive if you try to say it's not a planet. You don't mess with the Oracle.
 
My problem with considering Pluto a planet is this. We can divide the solar system's large bodies up into three discrete categories: Rocky planets (Mercury, Venus, Earth, Mars), gas giants (Jupiter, Saturn, Uranus, Neptune), and Pluto. Pluto isn't a gas giant, and it isn't a rocky planet like the others - it orbits too far away, eccentrically, sometimes coming inside the orbit of Neptune. It falls into a category all of its own.

Except that it doesn't. It is similar to other trans-Neptunian Kuiper Belt objects like Makimaki and Haumea. Let's put it in the same category as them.
 
arthwollipot said:
My problem with considering Pluto a planet is this. We can divide the solar system's large bodies up into three discrete categories: Rocky planets (Mercury, Venus, Earth, Mars), gas giants (Jupiter, Saturn, Uranus, Neptune), and Pluto. Pluto isn't a gas giant, and it isn't a rocky planet like the others - it orbits too far away, eccentrically, sometimes coming inside the orbit of Neptune. It falls into a category all of its own.

Except that it doesn't. It is similar to other trans-Neptunian Kuiper Belt objects like Makimaki and Haumea. Let's put it in the same category as them.
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There's more than two categories of stars. Why can't there be more than two categories of planets?

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.
 
arthwollipot said:
My problem with considering Pluto a planet is this. We can divide the solar system's large bodies up into three discrete categories: Rocky planets (Mercury, Venus, Earth, Mars), gas giants (Jupiter, Saturn, Uranus, Neptune), and Pluto. Pluto isn't a gas giant, and it isn't a rocky planet like the others - it orbits too far away, eccentrically, sometimes coming inside the orbit of Neptune. It falls into a category all of its own.

Except that it doesn't. It is similar to other trans-Neptunian Kuiper Belt objects like Makimaki and Haumea. Let's put it in the same category as them.
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Sure! Why not? The Terrestrial Planets, the Asteroids, the Jovian Planets, the Kuiper Belt Planets (Pluto, Charon, Eris, Makemake, Haumea, Sedna, etc...).
 
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