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A proposal to change the definition of a planet

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I ran across this article from a current events program.

CBC article link

Yes, it would re-classify Pluto as a planet again, as well as add a lot more planets to the list.

Knowing this is still a heated topic, please keep a calm head in the discussion. Have fun!

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YEEESS! PLUTO WILL FINNALY BE RECOGNISED IN ALL OF ITS GLORY AS A TRUE PLANET!!!!
PLUTO!!! PLUTO!!! PLUTO!!!

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@StupidAndy No, I mean I am sure there are asteroids that are spheroids. They would be considered a planet. 

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PLUTO!!! PLUTO!!! PLUTO!!!

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Nope. That's dumb. Ceres is not a planet. Neither are half the KBOs.

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I see all the effort and energy that has gone into bandying words and can't wrap my mind around it.

It makes no difference!

Classifications are more abstract than modern art. It is completely irrelevant in which category somebody puts Pluto. It is still exactly the same old Pluto. It doesn't get any more or less love, attention or funding either way.

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Quote

 

Or, in other words, says Runyon, "Anything round in space that's smaller than a star is a planet."

So, they really want to learn another couple hundred (thousand) planet names?  Per solar system? 

Sounds very tedious for very little reward.  For example,

Quote

 

and a survey in the infrared wavelengths has shown that the asteroid belt has 0.7–1.7 million asteroids with a diameter of 1 km or more (

https://en.wikipedia.org/wiki/Asteroid_belt)

So in the asteroid belt we've got *(likely) over a million planets now.  And those are just the ones over 1km in diameter.  Yeah, that makes everything easier, doesn't it?

Seems like a whole heck of a lot of inconvenience just for the sake of Pluto being embarrassed about being called a dwarf planet.

Edited by Slam_Jones

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Any definition of "planet" is necessarily arbitrary, and the new definition is no more arbitrary than the one which "demoted" Pluto (if you think it was a demotion). This new definition has the advantage of being more precise in its favor... 

My only problem with the last definition, is that it contains none of the required math. "has cleared the neighborhood around its orbit" is incredibly vague. Yes, there are mathematical definitions of this---in which case the definition should use them. There are a few different criteria proposed, but whichever one it is, say Lambda, then say Λ >1 or whatever they prefer.

The trouble with the clearing criteria, is that it result in a rather more ephemeral state than I might prefer. A planet could cease to be a planet because another body temporarily approaches, then become a planet again as it passes? What about Neptune, since after all the fact of Pluto crossing Neptune somehow indicts Pluto, but not Neptune?

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26 minutes ago, tater said:

The trouble with the clearing criteria, is that it result in a rather more ephemeral state than I might prefer. A planet could cease to be a planet because another body temporarily approaches, then become a planet again as it passes? What about Neptune, since after all the fact of Pluto crossing Neptune somehow indicts Pluto, but not Neptune?

That's not how the parameters work, they just determine if a body is likely to be gravitationally dominant in it's area of the solar system. Neptune indisputably is, that's why it's forced Pluto into a resonance.

26 minutes ago, tater said:

My only problem with the last definition, is that it contains none of the required math. "has cleared the neighborhood around its orbit" is incredibly vague. Yes, there are mathematical definitions of this---in which case the definition should use them. There are a few different criteria proposed, but whichever one it is, say Lambda, then say Λ >1 or whatever they prefer.

At least in our solar system it doesn't really matter which definition is used, because there are no edge cases; the line between the eight planets (and planet nine, should it exist) is extremely stark, so the natural division is obvious. If we take Soter's version, for example, the lowest value for the eight planets is Mars' at 5.1 × 103; and the highest for a dwarf planet is Ceres at 0.33; four orders of magnitude difference.

Edited by Kryten
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I cannot comprehend why people care so much about this....

I don't often quote shakespeare, but "A rose by any other name would smell as sweet"

We all know what pluto is when we talk about it, we all know what dwarf planets are when we talk about them... isn't that enough?

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I personally agree that the proposed definition above is better and more describing than the one currently in use. I not only have no problem with Ceres, the Moon, Ganymede, et. al. being planets, I think it's logical. I also see no need to make school children memorize them.

That said, I don't understand the hubbub about it either. Pluto is as incapable of caring what you call it as Shakespeare's rose is.

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43 minutes ago, tater said:

Any definition of "planet" is necessarily arbitrary, and the new definition is no more arbitrary than the one which "demoted" Pluto (if you think it was a demotion). This new definition has the advantage of being more precise in its favor... 

My only problem with the last definition, is that it contains none of the required math. "has cleared the neighborhood around its orbit" is incredibly vague. Yes, there are mathematical definitions of this---in which case the definition should use them. There are a few different criteria proposed, but whichever one it is, say Lambda, then say Λ >1 or whatever they prefer.

The trouble with the clearing criteria, is that it result in a rather more ephemeral state than I might prefer. A planet could cease to be a planet because another body temporarily approaches, then become a planet again as it passes? What about Neptune, since after all the fact of Pluto crossing Neptune somehow indicts Pluto, but not Neptune?

From what I can tell, "clearing the neighbourhood" means that there is nothing else of significant mass anywhere near the orbit of the planet. Pluto is not of significant mass compared to Neptune.

Edited by mikegarrison

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The problem stems from the fact that we are starting to realize that there are hundreds, thousands, perhaps even dozens of pluto-like objects in the solar system.

It's not that because of the definition chosen, Pluto no longer “qualifies” as a planet. It's that they wanted Pluto (like) planets to be no longer considered a planet and came up with a definition that did just that.

 

Ironically, a much shorter definition would have achieved the same and kept Pluto as a planet:

Planets in the solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

But I guess that's not "scientific" enough.

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I have no trouble with the concept, I just think it should be expressed unambiguously. The English statement as it is, is ambiguous. It is certainly possible to unambiguously define "clear" and "neighborhood." Put the mathematical parameters in, in short. Such a definition should apply to any planets, anywhere, in other words---give someone the masses, orbital parameters, etc, and they can tell you it's a planet. The confusion will only increase over time with more and more data about other solar systems forthcoming over the coming centuries. 

Take young solar systems. Are planets only planets when the solar system is mature? 

My point is that the definition is more useful if it is more universal, otherwise it's little different than saying planets are planets for historical reasons (say keeping Pluto in spite of other definitions).

Edited by tater

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1 hour ago, Slam_Jones said:

So, they really want to learn another couple hundred (thousand) planet names?  Per solar system? 

Sounds very tedious for very little reward.  For example,

So in the asteroid belt we've got *(likely) over a million planets now.  And those are just the ones over 1km in diameter.  Yeah, that makes everything easier, doesn't it?

Seems like a whole heck of a lot of inconvenience just for the sake of Pluto being embarrassed about being called a dwarf planet.

Most of those asteroids aren't round. Ceres is the only round object (due to gravity) in the Belt.

Who is this "they"? Kids in school? Planetary scientists? Astronomers? Even if there were thousands of "planets" we can just tell them about the big ones which are "major" planets. This argument doesn't really work. We already have thousands/millions of asteroids, there'd be no problem with hundreds or even thousands of planets (of which there would be regardless). The assumption that the word "planet" implies that something is special has already gone out the window, especially after we've seen thousands of other planets outside our own solar system.

Another problem is that the category "planet" does not include "dwarf planet", which is really just a clever little way to scoot around the issue of Pluto still being a planet.

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40 minutes ago, Kerbart said:

The problem stems from the fact that we are starting to realize that there are hundreds, thousands, perhaps even dozens of pluto-like objects in the solar system.

It's not that because of the definition chosen, Pluto no longer “qualifies” as a planet. It's that they wanted Pluto (like) planets to be no longer considered a planet and came up with a definition that did just that.

 

Ironically, a much shorter definition would have achieved the same and kept Pluto as a planet:

Planets in the solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

But I guess that's not "scientific" enough.

There actually was a footnote to the IAU resolution that said “Planets in the solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

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Those are alternative facts. Or fake news, or whatever. These are my alternative.

Let's see :

- Ganymede is beautiful, damply compelling, and spherical, yet not a planet.

- Titan is beautiful, have it's own hydrocarbon cycle, and spherical, yet not a planet.

- Io is beautiful, dangerously compelling, and spherical, yet not a planet.

- The Moon is lusting for space advocates, reachable, and spherical, yet not a planet.

None of the dwarf planets are as huge as these bodies, that aren't a planet. Ergo, the dwarf planet should not be a planet, no matter how beautiful they are. Studies for them shall not be blinded by classification.

Edited by YNM
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Classification is always sort of goofy. Look at the variant species definitions. Cannot successfully breed is one, while it is also could breed, but the critters chose not to. Alternately could breed, but they are geographically isolated. Paleontology uses bone morphology for cladistics---because they have little else to work with. Classifying worlds is little different, and such classification only becomes useful when you need to start sorting things into types for one or another reason, at which point you use the type of sorting that suits the purpose.

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I'm kind of over this emotional insistence that Pluto is a planet. It went from being the last and least among planets and became the first and greatest in a whole new important class of objects. Just like what happened to Ceres.

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PLUTO. IS. A. PLANET.

no matter what, never less then, always greater then.

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11 minutes ago, StupidAndy said:

PLUTO. IS. A. PLANET.

Science does not seem to support this statement.

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27 minutes ago, StupidAndy said:

PLUTO. IS. A. PLANET.

no matter what, never less then, always greater then.

Well, since the we as humans have assigned a group of people to define what  is a planet and what is not, since their definition does not classify Pluto as a planet, Pluto is not a planet. 

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54 minutes ago, StupidAndy said:

PLUTO. IS. A. PLANET.

Pluto is smaller than the Moon.

I kind of feel your pain. I grew up *knowing* that dinosaurs were giant, cold-blooded lizards who all died out millions of years ago. It took me something like a decade to finally accept that it really was true that birds are dinosaurs. But I've come to enjoy that when I watch the birds in my backyard, I'm watching living, breathing dinosaurs.

Someday you may come to enjoy Pluto for what it is, rather than resent that it isn't what you used to think it was.

Edited by mikegarrison
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1 hour ago, StupidAndy said:

PLUTO. IS. A. PLANET.

no matter what, never less then, always greater then.

Then stick with that. For yourself. It is as well, for most of the rest, just with a "Dwarf -".

1 hour ago, mikegarrison said:

... But I've come to enjoy that when I watch the birds in my backyard, I'm watching living, breathing dinosaurs. ...

And enjoy eating them XD chickens are dinosaurs !

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58 minutes ago, mikegarrison said:

Pluto is smaller than the Moon.

Speaking of moons...

We're in a similar situation, but kind of weirder. We have a moon in orbit over Jupiter that's bigger than a planet, but we also have asteroid moons that are just as much moons as Ganymede. We could try and be consistent, and start calling most moons something else entirely, or we could just stop caring and just call things "moons" if they orbit something that's not a star, and call things that are big enough to be round that orbit stars "planets." There would be no issue in having hundreds or even thousands of planets. We have more asteroids than that in the Belt. It obviously doesn't matter, at least from that perspective. Maybe there is a perspective where it matters, but I don't see one... We could just rearrange our nifty Venn diagram to include every category with "planet" in the name as a planet (satisfies the Pluto fans, as it's now a planet) and add a new category called "major planet," where it's a major planet if it's a planet that has cleared its neighborhood. Or we can leave the mess where it is and be done with it.

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