Pluto is was and always will be a planet

Mike! said:
Pluto is far from a minor character, having had shorts built exclusively around his activities...
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And so they should. You can’t have a dog appearing in movies with his activities dangling out in the open.
 
erwinl said:
'Disgracefully red carded'

People are way too much emotionally attached to a situation like this with Pluto.

Face it.
Whatever the criterium is for 'planet' status. The universe is big enough that there will be edge cases, which can mean they will fall on the planet side or the minor planet side of the equation, depending on how you look at it.
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Personally I don't mind the demotion. With all the new bodies that are being discovered it was just a matter of time before a more stringent classification system was adopted and some planets got the boot. I just wish they had picked a better name than "dwarf planet", which somehow includes the word "planet" but isn't one.
 
Ziggurat said:
Clearing one's neighborhood shouldn't be part of the definition of planet.
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Maybe, I don't disagree with you. But that's irrelevant: it IS part of the definition, and Pluto doesn't qualify. Neither does Ceres, even though it's clearly the biggest asteroid in the belt.

In any case, Pluto's orbit suggests a different origin than the eight canonical planets.
 
Belz... said:
Maybe, I don't disagree with you. But that's irrelevant: it IS part of the definition, and Pluto doesn't qualify.
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It's completely relevant, because the definition can be changed. That's how it became part of the definition in the first place: by changing it to include that criteria. And it should be changed again to remove it, because it's a crap criteria, for a whole host of reasons.

In any case, Pluto's orbit suggests a different origin than the eight canonical planets.
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So what?
 
Ziggurat said:
And four is cleaner than eight, so why not say that only Jupiter, Saturn, Uranus and Neptune are true planets? There's a much cleaner dividing line between Neptune and Earth than there is between Mercury and Pluto.

Choosing your criteria just to reduce the number of planets is cowardly. Be brave. Choose a solar system with 20+ planets.
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I don't think "why this definition and not this other one" is very useful to the discussion. Sounds too much like "why 15$ an hour and not 100?".

Ziggurat said:
It won't be the case with the earth forever either. The moon's orbital radius will eventually increase by roughly 40%, which should put the barycenter a bit outside the earth's surface. It would be strange for this gradual and smooth process to suddenly demote the earth from planet status.
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Not really. A status can change over time. It all depends on how you construct your classifications. Earth's moon is pretty damned big, compared to its primary.

Give it some credit here.
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I don't give rocks credit. They tend to spend it on booze and junk food.
 
Ziggurat said:
It's completely relevant, because the definition can be changed.
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No, it's irrelevant to what the definition IS. Currently that's the definition, and thus Pluto isn't a planet. If someone can make a good argument for further change they're welcome to do so. "Poor Pluto" doesn't qualify.

So what?
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So it's one more reason for a different classification. All classifications are arbitrary. We added one because the number of 'planets' was getting out of hand. How many planets are there in the solar system, you think, if we keep the old system ? 60,000?
 
Belz... said:
No, it's irrelevant to what the definition IS.
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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.

If someone can make a good argument for further change they're welcome to do so.
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Many have.

"Poor Pluto" doesn't qualify.
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Of course. I don't think anyone is saying that in seriousness, and I certainly don't take it seriously.

So it's one more reason for a different classification.
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It's not a good reason to classify it as not a planet.

All classifications are arbitrary. We added one because the number of 'planets' was getting out of hand. How many planets are there in the solar system, you think, if we keep the old system ? 60,000?
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There are not 60,000 bodies large enough to gravitationally pull themselves into spheroids.
 
Ziggurat said:
But we aren't only talking about what the definition is.
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No, we're not. You're right.

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.
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No, but it's useful if everyone means the same thing when we use words.

Many have.
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Let's heard yours. I have my own, by the way. But it still wouldn't include Pluto.

Of course. I don't think anyone is saying that in seriousness, and I certainly don't take it seriously.
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I really hope not. :)

It's not a good reason to classify it as not a planet.
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Why not? It's as good a reason as any. What's a good reason?

There are not 60,000 bodies large enough to gravitationally pull themselves into spheroids.
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You don't know that. We found quite a few of them in just a few years and in a very small portion of the solar system. There indeed may be thousands.
 
The Solar System:
Age: 4.568 billion years.
Address: Orion-Cygnus arm of the Milky Way Galaxy.

- 1 G-Type Main Sequence white/yellow dwarf Star
- 4 Rocky, terrestrial planets.
- 4 Gas Giants
- 5 Dwarf Planets (5 named, multiple likely further candidates)
- Unknown quantity (at least 778,897) of Minor Planets
- 525 natural satellites (185 planetary, 347 minor planetary)
- Asteroid Belt, Kuiper Belt, Oort Cloud, may various trans-Neptuian objects.
- At least 4,017 comets
- 1 Teapot (Status contested)
 
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Belz... said:
Let's heard yours. I have my own, by the way. But it still wouldn't include Pluto.
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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.

I'm open to arguments to narrow this down a little more, perhaps with a mass or diameter threshold, but clearing your neighborhood is a bad criteria. For one thing, it's hard to tell if a neighborhood has been sufficiently cleared (none of the solar system is totally cleared, so this requires some sort of threshold for what counts as cleared). 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.

Why not?
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Because the definition shouldn't be history-dependent.

You don't know that. We found quite a few of them in just a few years and in a very small portion of the solar system. There indeed may be thousands.
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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.
 
JoeMorgue said:
But it has to be as we gain further knowledge or we are forever bound to definitions that don't make sense anymore.
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I was referring to the history of the object under consideration, not the history of the word. So the present properties of an object should determine whether or not it's a planet, not what the object's past history is.
 
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Ziggurat said:
I was referring to the history of the object under consideration, not the history of the word. So the present properties of an object should determine whether or not it's a planet, not what the object's past history is.
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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?
 
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