# 12 Planets?



## Pbartender (Aug 18, 2006)

I almost forgot to post this here...

The IUA finally has a draft proposal for the definition of a planet...

The new suggested guidelines would add Ceres, Charon and 2003 UB313 ("Xena") to the list of planets.

The proposed guidelines are essentially:

Must orbit the sun (or any star).
Must a "round" object.
Must be at least 800 km in diameter.
Must be at least 1/12,000th the mass of Earth.
Moons may qualify only if the common center of gravity of it and its planet does not lie below the surface of the planet.


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## Piratecat (Aug 18, 2006)

How cool is it that Xena's moon is named Gabrielle?

Hey, you may know this.  Why is Charon considered a new planet? Isn't it Pluto's moon?


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## Ilium (Aug 18, 2006)

Piratecat said:
			
		

> How cool is it that Xena's moon is named Gabrielle?
> 
> Hey, you may know this.  Why is Charon considered a new planet? Isn't it Pluto's moon?



 Yes, but it's big enough to become round under its own gravity and is almost as big as Pluto, so they're considered a double-planet system.


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## Cheiromancer (Aug 18, 2006)

The barycenter (center of gravity for the system) is between Pluto and Charon.  Unlike the barycenter of the Earth and the Moon, which is 1700 km below the surface of the Earth.

There's a good thread about it at circvsmaximvs.com, in the Machinator forum.

Pluto's status to be decided, finally


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## Thunderfoot (Aug 18, 2006)

Piratecat said:
			
		

> How cool is it that Xena's moon is named Gabrielle?
> 
> Hey, you may know this.  Why is Charon considered a new planet? Isn't it Pluto's moon?



But not for long...(It's only a temporary name) thankfully.  We have allt hese beautifully named planets that have some sort of historical significance and then the geeks muck it up with Xena and Gabrielle... pitiful.


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## Pbartender (Aug 19, 2006)

Thunderfoot said:
			
		

> But not for long...(It's only a temporary name) thankfully.  We have allt hese beautifully named planets that have some sort of historical significance and then the geeks muck it up with Xena and Gabrielle... pitiful.




I'm rather hoping that they start naming all the new Kuiper Belt planets after Lovecraft's Great Old Ones...  Zhar and Lloigor would make a much better pair of outer planets than Xena and Gabrielle.


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## Arkhandus (Aug 19, 2006)

Phooey.  I spit on the geeks who nicknamed planets/moons Xena and Gabrielle (or would if I could).  It's no more appropriate than naming them Moe and Curly, except more people would probably prefer the latter names.  Stick with the good ole' classical Greek/Roman planet and moon naming conventions.

I'd much rather see them name the 10th/11th planet (I really don't like the thought of considering Charon a planet itself, but if I bothered to check into the scientific reasoning and stats behind it, I might change my mind and be okay with it) Nox (Roman) or Nyx (Greek) and the moon Erebus, in keeping with Pluto and Charon being named after entities of the underworld from Greek/Roman mythology.


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## trancejeremy (Aug 19, 2006)

Ack. I'm not sure what would be worse than naming planets Xena and Gabrielle. I guess maybe after the cast of "Wings" or after Paris Hilton. But even Gary Coleman would be an improvement.

Still, Charon is actually named after the discover's wife. (IIRC, Sharon, but he had the decency to Roman-Greco it)


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## Ilium (Aug 19, 2006)

I'm gonna buck the trend: I like the names Xena and Gabrielle.  I'm sure they won't stick, but I think they're great.

If we really wanted to be fair we'd spread the wealth a little.  Why not name one of the planets Osiris, or Tuoni or some other god(dess) of the underworld?  Hel would be good, and quite descriptive.


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## mythusmage (Aug 19, 2006)

Xena: Orcus (god of the dead)
Gabriele: Acca Larentia (god of good deceased spirits)


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## Pbartender (Aug 19, 2006)

Ilium said:
			
		

> I'm gonna buck the trend: I like the names Xena and Gabrielle.  I'm sure they won't stick, but I think they're great.




I don't particularly like those names, but I certainly dont' understand why so many complain about them...  It's widely known that Xena and Gabrielle are just temporary nicknames (and a lot easier to say than "2003 UB313") until something permanent can be thought up, and they're mostly used as a joke, besides.



			
				Ilium said:
			
		

> If we really wanted to be fair we'd spread the wealth a little. Why not name one of the planets Osiris, or Tuoni or some other god(dess) of the underworld? Hel would be good, and quite descriptive.




Actually, we already have "minor planets" named Sedna, an Inuit ocean goddess, Quaoar, the Tongva creator god, and Varuna, a Hindu god of the sky, rain, the celestial ocean, law and the underworld...  They're all on the short list for consideration as additional planets.

http://upload.wikimedia.org/wikipedia/en/7/72/Iau_dozen.jpg



			
				mythusmage said:
			
		

> Xena: Orcus (god of the dead)




Sorry, Orcus is already taken. (See link above.)



			
				Arkhandus said:
			
		

> (I really don't like the thought of considering Charon a planet itself, but if I bothered to check into the scientific reasoning and stats behind it, I might change my mind and be okay with it)




If you bothered to read the first post in the thread (and several that came after), you'd have all the scientific reasoning and stats you require...


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## BlueBlackRed (Aug 19, 2006)

I was under the impression that all planets were given Roman god names, and the next planet named was set to be, indeed, Vulcan.


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## Dannyalcatraz (Aug 19, 2006)

> I was under the impression that all planets were given Roman god names, and the next planet named was set to be, indeed, Vulcan.




Fascinating, Captain.   

I think if we find another large planet with a bunch of moons, we should name it Orpheus (or perhaps Terpsichore).

Then we name the first moon we discover "Clapton," since, as the graffiti says, he is God...

Of course, we'd have to follow that up with other moons named Hendrix, May, Segovia, Gilmour, Johnson, Satriani, Malmsteen, and so forth.*

*I'm just using guitarists...any kind of talented musician would be worthy- Orbison, Popper, Wonder, Hancock...


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## Ranger REG (Aug 19, 2006)

BlueBlackRed said:
			
		

> I was under the impression that all planets were given Roman god names, and the next planet named was set to be, indeed, Vulcan.



*raises a Vulcan eyebrow*

Fascinating.

Unfortunately, I wouldn't want to colonize there. I might be subjected to a condition where my sex drive peaks once every seven years.


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## Jdvn1 (Aug 19, 2006)

Piratecat said:
			
		

> How cool is it that Xena's moon is named Gabrielle?



They did that on purpose.

And that CNN article isn't great. I recommend you read these (the source):
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html
and because everyone seems to think there's a huge throng of astronomers trying to make Pluto not a planet (there isn't):
http://www.iau2006.org/mirror/www.iau.org/STATUS_OF_PLUTO.238.0.html


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## MavrickWeirdo (Aug 19, 2006)

Years ago some scientists tried to get the scientific community to stop calling Pluto a planet (Which is noted in the Christine Lavin song _"Planet X"_) because it didn't fit all the definitions of a planet. The campaign failed, and the definition of Planet was re-written to remove ambiguity.

As a result of the re-written definition we have 3 more heavenly bodies which qualify for planet status.


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## Pbartender (Aug 19, 2006)

Dannyalcatraz said:
			
		

> I think if we find another large planet with a bunch of moons, we should name it Orpheus (or perhaps Terpsichore).




Orpheus (or Theia) is the name of the hypothetical planet that collided with Earth to make the moon.

Terpsichore is already an asteroid.



			
				MavrickWeirdo said:
			
		

> Years ago some scientists tried to get the scientific community to stop calling Pluto a planet (Which is noted in the Christine Lavin song _"Planet X"_) because it didn't fit all the definitions of a planet. The campaign failed, and the definition of Planet was re-written to remove ambiguity.




Actually, there never was a formal definition of what a planet was...  Up until now, the definition of a planet was, essentially, "Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto are planets."

Pluto was a planet simply because the IAU said it was, not because it met any qualifying criteria.



			
				MavrickWeirdo said:
			
		

> As a result of the re-written definition we have 3 more heavenly bodies which qualify for planet status.




Also be aware that even thought the new proposal is likely to pass, it still needs to be voted on and isn't official just yet.


Oh, and thanks, Jdvn1, for the IAU articles...  I posted the CNN link, since that's where I saw it first and neglected to follow up.


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## mythusmage (Aug 20, 2006)

You must admit the new definition of what a planet is is a Ceres attempt to rectify the problem.


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## Thunderfoot (Aug 20, 2006)

mythusmage said:
			
		

> You must admit the new definition of what a planet is is a Ceres attempt to rectify the problem.



Boooo!!! HISSSSSSS! Booooooo!

If I recall correctly, Neptune and Pluto were named becuase of the representative surfaces (Blue like the ocean and Black like Hel) through telescopes.  It would make sense that the two new planets would be named according to their features; what they may be or the names that would fit them are unknown to me, but I would like to see the trend continue.


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## Jdvn1 (Aug 20, 2006)

Pbartender said:
			
		

> Oh, and thanks, Jdvn1, for the IAU articles...  I posted the CNN link, since that's where I saw it first and neglected to follow up.



I've actually been following up the IAU for years. That's where I first got my information.  It's important to note, I think, that they list _different_ definitions of a planet...


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## Richards (Aug 20, 2006)

Today's "Sheldon" strip was pretty topical, I thought:

http://www.sheldoncomics.com/comics/sheldon/archive/sheldon-20060820.html

Johnathan


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## Jdvn1 (Aug 21, 2006)

Richards said:
			
		

> Today's "Sheldon" strip was pretty topical, I thought:
> 
> http://www.sheldoncomics.com/comics/sheldon/archive/sheldon-20060820.html
> 
> Johnathan



 Pretty funny.

I just feel compelled to mention that they didn't redefine "planet" and that the definition wasn't designed to fit majority decision.


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## BOZ (Aug 21, 2006)

i just think it would be totally cool if they named a planet Orcus.


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## Zander (Aug 21, 2006)

Arkhandus said:
			
		

> I'd much rather see them name the 10th/11th planet (I really don't like the thought of considering Charon a planet itself, but if I bothered to check into the scientific reasoning and stats behind it, I might change my mind and be okay with it) Nox (Roman) or Nyx (Greek)...



One of Pluto's moons is already called Nix so that would rule out Nyx on the grounds that they're too similar.

I'm in favour of naming a planet Gygax.


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## Piratecat (Aug 21, 2006)

Jdvn1 said:
			
		

> They did that on purpose.



With great respect, duh.  

Seriously, I know. I just think it's funny. It lacks the proper gravitas, but I smile every time I think of it.


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## Pbartender (Aug 21, 2006)

BOZ said:
			
		

> i just think it would be totally cool if they named a planet Orcus.




There already is...  See above.


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## BOZ (Aug 21, 2006)

oh, well then that's totally cool.


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## occam (Aug 21, 2006)

Pbartender said:
			
		

> Actually, there never was a formal definition of what a planet was...  Up until now, the definition of a planet was, essentially, "Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto are planets."
> 
> Pluto was a planet simply because the IAU said it was, not because it met any qualifying criteria.
> 
> Also be aware that even thought the new proposal is likely to pass, it still needs to be voted on and isn't official just yet.




It's going to be ridiculous if this new proposal passes. So now we'll have a new planet between Mars and Jupiter? And much worse, as more and more large Kuiper Belt objects are discovered, textbooks will be outdated before they're published. It'll be impossible to keep up. A year or two from now, we could be looking at a solar system with dozens of "planets", and more on the way.

Pluto needs to get dropped from the roster. Other than history, pretty soon we'll see there's nothing that distinct about it compared to dozens, or hundreds, or possibly thousands of other rocky ice balls out beyond Neptune. At least with the other 8, we can expect to keep the number of planets stable.


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## Pbartender (Aug 21, 2006)

occam said:
			
		

> And much worse, ... textbooks will be outdated before they're published. It'll be impossible to keep up.




How is it that different from the current situation?



			
				occam said:
			
		

> Pluto needs to get dropped from the roster. Other than history, pretty soon we'll see there's nothing that distinct about it compared to dozens, or hundreds, or possibly thousands of other rocky ice balls out beyond Neptune. At least with the other 8, we can expect to keep the number of planets stable.




Oh, come now, that's historical cussedness talking too...  "We've only ever had 9 planets!  We don't want more! In fact, let's get rid of one!"

 

But that's the whole point...  We're learning that there's a lot more floating around our solar system than we ever thought.  It's the interplanetary equivalent of Balboa crossing Panama and finding out that, "Hey! There's a whole other ocean over here!"


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## Ranger REG (Aug 21, 2006)

Zander said:
			
		

> I'm in favour of naming a planet Gygax.



Oh, great.  :\ 

All we need is a bunch of geekish colonists to call themselves Gygaxians.


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## Umbran (Aug 22, 2006)

occam said:
			
		

> Other than history, pretty soon we'll see there's nothing that distinct about it compared to dozens, or hundreds, or possibly thousands of other rocky ice balls out beyond Neptune.




Well, there'll be something other than history to make Pluto distinct - it is large enough to have gravitational effects that can be detected, and both large and close enough to see with a decent telescope.

The proposal is, if I recall correctly, to have a separate category for the iceballs - "plutons".  Not that having the number of "planets" be small is really a meaningful goal, but they can be excluded from some discussions as a separate class of object.



			
				pbartender said:
			
		

> # Must a "round" object.
> # Must be at least 800 km in diameter.
> # Must be at least 1/12,000th the mass of Earth.




I think, more technically, the body has to have come to a round shape under the effects of it's own gravity - the size and mass limitations are there mostly because they describe the typical point at which this happens.


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## ssampier (Aug 22, 2006)

I suggest we name the 2003 UB313 planet "Xenu" instead.



			
				Ranger REG said:
			
		

> Oh, great.  :\
> 
> All we need is a bunch of geekish colonists to call themselves Gygaxians.




Well, he was _one_ of the few "things" left after the Universe collapsed on itself.


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## occam (Aug 22, 2006)

Pbartender said:
			
		

> How is it that different from the current situation?




Drop Pluto, and make a one-time change. Add Pluto and an ever-expanding number of other small things... It's completely different, that's the point.



			
				Pbartender said:
			
		

> Oh, come now, that's historical cussedness talking too...  "We've only ever had 9 planets!  We don't want more! In fact, let's get rid of one!"
> 
> 
> 
> But that's the whole point...  We're learning that there's a lot more floating around our solar system than we ever thought.




Sure, but does that mean they're all "planets"? We don't feel compelled to call comets "planets", why does Pluto need to be one, other that "historical cussedness"? Actually, with this proposal, if there were a big enough comet, it would be a "planet".


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## occam (Aug 22, 2006)

Umbran said:
			
		

> Well, there'll be something other than history to make Pluto distinct - it is large enough to have gravitational effects that can be detected, and both large and close enough to see with a decent telescope.




That's an accident of placement. Just because Pluto's closer doesn't make it fundamentally different than all the other KBOs out there.



			
				Umbran said:
			
		

> I think, more technically, the body has to have come to a round shape under the effects of it's own gravity - the size and mass limitations are there mostly because they describe the typical point at which this happens.




But "roundness" is a completely meaningless distinction. It doesn't help categorize objects according to how they were formed, orbital characteristics, rotational characteristics, composition, ... i.e. things that actually matter. Should Ceres really be in a whole different class of objects than other asteroids? Should Pluto (and Charon) really be classified differently than the uncounted horde of slightly smaller objects in the Kuiper Belt?


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## Umbran (Aug 22, 2006)

occam said:
			
		

> That's an accident of placement. Just because Pluto's closer doesn't make it fundamentally different than all the other KBOs out there.




Who said that classifying a thing as a "planet" meant it was fundamentally different from all  other classes?  Quite the contrary - most planets also fit into other classes.  Some planets are gas giants.  Others are rocky worlds.  Why not have a dirty iceball planet?

Accidents of placement should not be overlooked - the Jovian moons are going to remain classified as satellites, though in size and structure many of them are very planet-like.  The difference is only accident of placement.

But, to handle exactly your problem, the official category of "plutons" is part of the new definition.



> But "roundness" is a completely meaningless distinction. It doesn't help categorize objects according to how they were formed, orbital characteristics, rotational characteristics, composition, ... i.e. things that actually matter.




But "planet" never officially referred to any of those things anyway, so I don't see the problem.   A couple of things you mention - like rotational characteristics and composition - I don't feel have anything to do with the characterization as a planet.  When Earth, tiny resonant and eccentric Mercury, and sideways gas giant Uranus are all covered by the definition "planet", the definition has to be rather broad.

That an object has enough mass that gravitation overcomes rigid-body forces so it can come to a form of hydrostatic equilibrium (and thus be round) says some significant things about the object.  



> Should Ceres really be in a whole different class of objects than other asteroids?




I think Ceres is a very good illustration of the fact that any definition clear enough to be useful will have annoying edge cases.  The Universe is only occasionally digital - it will create a continuum of objects no matter how finely we decide to split hairs between distinct classes.  No matter what the definition, we can find or imagine a case that will be troublesome.  So, I'm not too concerned about it.


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## occam (Aug 22, 2006)

Umbran said:
			
		

> Who said that classifying a thing as a "planet" meant it was fundamentally different from all  other classes?




What's the point of a classification other than to draw essential distinctions? The distinction of roundedness isn't scientifically interesting, in and of itself.



			
				Umbran said:
			
		

> Quite the contrary - most planets also fit into other classes.  Some planets are gas giants.  Others are rocky worlds.  Why not have a dirty iceball planet?




No, they don't. Planets are not asteroids, nor comets, nor meteors, nor stars, nor moons. These are all orthogonal categories, that relate to details of formation, composition, etc. That the category of "planets" may also be subcategorized into gas giants and rocky planets doesn't change that.

The proposed definition of "planet" only means "big, orbiting a star, but not a star itself". How is that useful? You still need a way to refer to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune as different from everything else in the Solar System, including Ceres and any large KBOs (including Pluto and Charon). What do you call them, then? "Planets that aren't also asteroids or KBOs or large examples of some other things?" Or do you just call them planets, with the unspoken caveat that you really don't mean to include Ceres?



			
				Umbran said:
			
		

> Accidents of placement should not be overlooked - the Jovian moons are going to remain classified as satellites, though in size and structure many of them are very planet-like.  The difference is only accident of placement, not one of just placement.




The large Jovian moons, and Titan, and Triton and other large moons (including Earth's) formed differently than the planets around which they orbit. It's an important distinction.



			
				Umbran said:
			
		

> A couple of things you mention - like rotational characteristics and composition - I don't feel have anything to do with the characterization as a planet.  When Earth, tiny resonant and eccentric Mercury, and sideways gas giant Uranus are all covered by the definition "planet", the definition has to be rather broad.




Limiting the discussion to objects in the Solar System*: Planets orbit the Sun. They all orbit within the ecliptic (not counting Pluto), and in the same direction. They all have nearly circular orbits (not counting Pluto). They all have substantial atmospheres (not counting Pluto, or Mercury, which has extenuating circumstances). They all probably formed in a similar manner (possibly not counting Pluto). Taken together, those characteristics help define a useful category of objects (which can be further subcategorized).

* No doubt, future discoveries in other star systems will muddy the waters, but we're not quite there yet.



			
				Umbran said:
			
		

> That an object has enough mass that gravitation overcomes rigid-body forces so it can come to a form of hydrostatic equilibrium (and thus be round) says some significant things about the object.




No, it doesn't, other than that it happens to be big (or more specifically, massive). By itself, it doesn't provide any real insight into the processes of formation, so limiting the definition of planethood to this one thing (OK, two things, with the star-orbiting criterion) doesn't further any discussion. You still need to make further distinctions, so what's the point, other than to allow Pluto to retain its legacy status?



			
				Umbran said:
			
		

> I think Ceres is a very good illustration of the fact that any definition clear enough to be useful will have annoying edge cases.




Pluto _is_ the edge case! Heck, it's not really even an edge case; it's been an oddball inclusion from the start. Drop it, and there's no further confusion (in this star system, at least).


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## Pbartender (Aug 22, 2006)

occam said:
			
		

> What's the point of a classification other than to draw essential distinctions? The distinction of roundedness isn't scientifically interesting, in and of itself.




You are greatly mistaken.  Being naturally round is an rather extraordinary phenominon, no matter how it happens.



			
				occam said:
			
		

> The proposed definition of "planet" only means "big, orbiting a star, but not a star itself". How is that useful?




Just as useful as calling a star, essentially, "a self-luminous gaseous spheroidal celestial body of great mass which produces energy by means of nuclear fusion reactions"...  

Or an animal "any of a kingdom (Animalia) of living things including many-celled organisms and often many of the single-celled ones that typically differ from plants in having cells without cellulose walls, in lacking chlorophyll and the capacity for photosynthesis, in requiring more complex food materials, in being organized to a greater degree of complexity, and in having the capacity for spontaneous movement and rapid motor responses to stimulation".

How are those useful?

You must start with a broad definition, then categorize by type...  Rocky dwarfs, Gas giants, Icy dwarfs, etc...



			
				occam said:
			
		

> No, they don't. Planets are not asteroids, nor comets, nor meteors, nor stars, nor moons. These are all orthogonal categories, that relate to details of formation, composition, etc. That the category of "planets" may also be subcategorized into gas giants and rocky planets doesn't change that.




So what?  All these guys are doing are stipulating the rules of the various orthogonal categories and then re-evaluating current know bodies in the solar system, and re-categorizing them.  Why is that such a problem?



			
				occam said:
			
		

> You still need a way to refer to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune as different from everything else in the Solar System, including Ceres and any large KBOs (including Pluto and Charon).




Why?  There's no reason for it.



			
				occam said:
			
		

> What do you call them, then? "Planets that aren't also asteroids or KBOs or large examples of some other things?" Or do you just call them planets, with the unspoken caveat that you really don't mean to include Ceres?




Likely, people will simply continue calling them the "major planets", though that won't technically be an official classification.



			
				occam said:
			
		

> The large Jovian moons, and Titan, and Triton and other large moons (including Earth's) formed differently than the planets around which they orbit. It's an important distinction.




Perhaps, but it's not normally a very good way to classify something...  Maybe in geology, but certainly not in astronomy, a subject in which it is generally very difficult to determine the origin of any object you are looking at.

Consider stars, for instance... They are primarily classified by what they ARE (size, mass, temperature, spectrum, elemental composition, etc...), not by what they used to be, or by how they came to be.



			
				occam said:
			
		

> Limiting the discussion to objects in the Solar System*: Planets orbit the Sun. They all orbit within the ecliptic (not counting Pluto), and in the same direction. They all have nearly circular orbits (not counting Pluto). They all have substantial atmospheres (not counting Pluto, or Mercury, which has extenuating circumstances). They all probably formed in a similar manner (possibly not counting Pluto). Taken together, those characteristics help define a useful category of objects (which can be further subcategorized).




Again, so what?  There's more than one way to classify any given group of things.

Just because you've only ever eaten red apples, doesn't mean that a green aple isn't an apple.



			
				occam said:
			
		

> By itself, it doesn't provide any real insight into the processes of formation, so limiting the definition of planethood to this one thing (OK, two things, with the star-orbiting criterion) doesn't further any discussion. You still need to make further distinctions, so what's the point, other than to allow Pluto to retain its legacy status?




So you propose to replace an easily measured and concrete qualification with a something that can, at best, be only theoretically guessed at?  Because, the simple fact is, we don't really have a very good idea of how the planets formed, or whether they formed differently from all the other debris floating about the solar system.

And what would you do with the moon, which has an especially unique theory to explain its formation?


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## occam (Aug 23, 2006)

Pbartender said:
			
		

> occam said:
> 
> 
> 
> ...




Those are functional definitions, not based on one simple surface feature. They provide useful information about the subjects being studied, and separate them from other things that are fundamentally different and that developed in different ways.

Ceres is no different from other asteroids because it's round. There's nothing fundamentally different between Pluto and legions of other KBOs. Why should they be classified differently? It's a useless distinction to make. 



			
				Pbartender said:
			
		

> All these guys are doing are stipulating the rules of the various orthogonal categories and then re-evaluating current know bodies in the solar system, and re-categorizing them.  Why is that such a problem?




Because the proposed definition of "planet" is NOT orthogonal. It includes "true" planets, as well as asteroids and KBOs. Why do that?



			
				Pbartender said:
			
		

> occam said:
> 
> 
> 
> ...




From what we can currently hypothesize about the formation of bodies in the Solar System, the eight objects known as "planets" (not counting Pluto) all probably formed similarly. You can discuss theories of planet formation that apply to all eight. If you include Ceres and KBOs, you can't do that. So you still need a way to distinguish those eight objects. What do you call them if you don't call them just "planets"?



			
				Pbartender said:
			
		

> Perhaps, but it's not normally a very good way to classify something...  Maybe in geology, but certainly not in astronomy, a subject in which it is generally very difficult to determine the origin of any object you are looking at.




Uh, so you're saying it's not worth classifying astronomical objects by supposed origin?



			
				Pbartender said:
			
		

> Consider stars, for instance... They are primarily classified by what they ARE (size, mass, temperature, spectrum, elemental composition, etc...), not by what they used to be, or by how they came to be.




They're classified by both. It just so happens that stars with common measurable characteristics have (or are presumed to have) similar origins.



			
				Pbartender said:
			
		

> Again, so what?  There's more than one way to classify any given group of things.




Not every way is a useful one.

The characteristics common to "true" planets that I listed are useful. They refer to fundamental differences and advance scientific discussion by prompting questions about why these objects have these common characteristics.

I'll turn this question around: Why should the proposed definition be used to define a "planet"? How does the consideration of simple roundedness advance scientific understanding? Why should slightly smaller asteroids and KBOs that aren't completely round be excluded? How are they fundamentally different from round things, in ways that point to scientifically interesting distinctions in composition, development, etc.?

Anyway, it's now looking like the IAU is getting its wits about it, and will vote out Pluto in a day or two. One way or another, my daughter's bedside poster will probably soon be out-of-date.  ;-)


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## Umbran (Aug 23, 2006)

occam said:
			
		

> What's the point of a classification other than to draw essential distinctions?




There are many possible points to classification, and which one you're trying to serve can determine which distinctions you ought to be dealing with, essential or otherwise.  



> The proposed definition of "planet" only means "big, orbiting a star, but not a star itself". How is that useful?




Historically, the term "planet" has had nothing to do with details of formation, or composition.  A term for "thing that orbits the sun that we can see reasonably easily" has served astronomers since the times of the Greeks, at least.  What we have here is merely a small refinement on that.   



> You still need a way to refer to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune as different from everything else in the Solar System, including Ceres and any large KBOs (including Pluto and Charon). What do you call them, then?




"Rocky world", "gas giant", "pluton", or "asteroid" as appropriate.  The terms for three of these thigns already existed, and the fourth is up for adoption now.  If you're aiming to make essential distinctions, then lumping gas giants and rocky worlds together is rather against your goal, as they are essentially different, in both composition and details of formation.



> The large Jovian moons, and Titan, and Triton and other large moons (including Earth's) formed differently than the planets around which they orbit. It's an important distinction.




Some would argue that Titan, and several other large moons, may have formed more like a planet than Luna.  And neither have much similarity to the origins of Phobos.  So, the term "moon" or "satellite" really has little to do with formation.  It's a matter of orbit, and that's about all.  



> Limiting the discussion to objects in the Solar System*: Planets orbit the Sun. They all orbit within the ecliptic (not counting Pluto), and in the same direction.




We already have several examples of extrasolar planets that orbit with largish inclinations, so that's already falling through as a distinction.



> They all have nearly circular orbits (not counting Pluto).




Mercury's eccentricity is nearly that of Pluto.  Most known extrasolar planets appear to have high eccentricities.  So I'd say goodbye to that criterion as well if I were you.



> They all have substantial atmospheres (not counting Pluto, or Mercury, which has extenuating circumstances).




That depends upon what you call "substantial".  Mars has only a wisp, less than that of the smaller, colder body of Titan.  I think Mars and Mercury long ago removed atmospheres from the general definition of "planet" in the eyes of the scientific community.



> They all probably formed in a similar manner (possibly not counting Pluto).




Possibly, possibly not.  Since we don't know, we really shouldn't be talking about excluding it yet on this basis, now should we?



> By itself, it doesn't provide any real insight into the processes of formation, so limiting the definition of planethood to this one thing (OK, two things, with the star-orbiting criterion) doesn't further any discussion.




It does - but it only deals with very basic discussion, which is reasonable for a very basic classification.  There are already terms for the finer distinctions, so there's no need to try to cram them into "planet".


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## Pbartender (Aug 23, 2006)

occam said:
			
		

> Those are functional definitions, not based on one simple surface feature. They provide useful information about the subjects being studied, and separate them from other things that are fundamentally different and that developed in different ways.




As does the proposed definition of a planet.  To use the IAU's own words, "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."

That's a pretty fundimental definition there.



			
				occam said:
			
		

> Ceres is no different from other asteroids because it's round.




Yes, it is.  Ceres is different because is "has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape".  Other asteroids don't.  Therefore, Ceres is fundimentally different than other asteroids.



			
				occam said:
			
		

> There's nothing fundamentally different between Pluto and legions of other KBOs. Why should they be classified differently?




They aren't, necessarily.  There's a short of of about a dozen other KBOs that could qualify for planethood jsut as easily as Pluto, if the resolution passes.



			
				occam said:
			
		

> Because the proposed definition of "planet" is NOT orthogonal. It includes "true" planets, as well as asteroids and KBOs. Why do that?




You're looking at it wrong.  The proposed definition includes a few objects that we used to consider asteroids and KBOs, and would be promoted to planets, if it passed.  



			
				occam said:
			
		

> From what we can currently hypothesize about the formation of bodies in the Solar System, the eight objects known as "planets" (not counting Pluto) all probably formed similarly. You can discuss theories of planet formation that apply to all eight. If you include Ceres and KBOs, you can't do that. So you still need a way to distinguish those eight objects. What do you call them if you don't call them just "planets"?




But it's all just thories, and that's the point.  What happens if in 20 years we discover that the theories aren't quite right, and planets, asteroids or KBOs didn't form in similar manners or even in the way we thought?  We'd have to reclassify everything, since we based or original classification on something that we weren't certain of to begin with.



			
				occam said:
			
		

> Uh, so you're saying it's not worth classifying astronomical objects by supposed origin?




Yes...  Precisely because you have to include the word "supposed" in that sentence.



			
				occam said:
			
		

> They're classified by both. It just so happens that stars with common measurable characteristics have (or are presumed to have) similar origins.




Yep... and that's a lucky coincidence.



			
				occam said:
			
		

> Not every way is a useful one.




Nope...  And in astronomy, supposed origin is not a very useful one.



			
				occam said:
			
		

> The characteristics common to "true" planets that I listed are useful. They refer to fundamental differences and advance scientific discussion by prompting questions about why these objects have these common characteristics.
> 
> I'll turn this question around: Why should the proposed definition be used to define a "planet"? How does the consideration of simple roundedness advance scientific understanding? Why should slightly smaller asteroids and KBOs that aren't completely round be excluded? How are they fundamentally different from round things, in ways that point to scientifically interesting distinctions in composition, development, etc.?




There's your problem.  Categories aren't meant to advance discussions and prompt questions.  They are simply there as an organizational tool. Something that can be used to definitively distinguish one set from another.

You can still discuss and ask questions regardless of whether or not a method of classification encourages that or not...  A classification method will never prevent such discussion.

Consider the means of disguishing planets from other objects...

With regards to planets, the first stipulation writes itself: A planet must orbit a star.

After that, you need to set a minimum and maximum size.  Again, the upper limit write itself...  We already have definitions for stars, so if the object qualifies as a star, it's too big and is disqualified from being a planet.  The lower limit is the tricky point.  When you take a good look at planets and asteroids, the one fundemental break point in size is when an object has enough mass to make itself round...  So that's what they used.

Finally, there are a lot of moons that could technically fit this description, so you add a moon stipulation...  the common center of gravity.


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## Pbartender (Aug 23, 2006)

occam said:
			
		

> Those are functional definitions, not based on one simple surface feature. They provide useful information about the subjects being studied, and separate them from other things that are fundamentally different and that developed in different ways.




As does the proposed definition of a planet.  To use the IAU's own words, "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."

That's a pretty fundimental definition there.



			
				occam said:
			
		

> Ceres is no different from other asteroids because it's round.




Yes, it is.  Ceres is different because is "has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape".  Other asteroids don't.  Therefore, Ceres is fundimentally different than other asteroids.



			
				occam said:
			
		

> There's nothing fundamentally different between Pluto and legions of other KBOs. Why should they be classified differently?




They aren't, necessarily.  There's a short of of about a dozen other KBOs that could qualify for planethood jsut as easily as Pluto, if the resolution passes.



			
				occam said:
			
		

> Because the proposed definition of "planet" is NOT orthogonal. It includes "true" planets, as well as asteroids and KBOs. Why do that?




You're looking at it wrong.  The proposed definition includes a few objects that we used to consider asteroids and KBOs, and would be promoted to planets, if it passed.  



			
				occam said:
			
		

> From what we can currently hypothesize about the formation of bodies in the Solar System, the eight objects known as "planets" (not counting Pluto) all probably formed similarly. You can discuss theories of planet formation that apply to all eight. If you include Ceres and KBOs, you can't do that. So you still need a way to distinguish those eight objects. What do you call them if you don't call them just "planets"?




But it's all just thories, and that's the point.  What happens if in 20 years we discover that the theories aren't quite right, and planets, asteroids or KBOs didn't form in similar manners or even in the way we thought?  We'd have to reclassify everything, since we based or original classification on something that we weren't certain of to begin with.



			
				occam said:
			
		

> Uh, so you're saying it's not worth classifying astronomical objects by supposed origin?




Yes...  Precisely because you have to include the word "supposed" in that sentence.



			
				occam said:
			
		

> They're classified by both. It just so happens that stars with common measurable characteristics have (or are presumed to have) similar origins.




Yep... and that's a lucky coincidence.



			
				occam said:
			
		

> Not every way is a useful one.




Nope...  And in astronomy, supposed origin is not a very useful one.



			
				occam said:
			
		

> The characteristics common to "true" planets that I listed are useful. They refer to fundamental differences and advance scientific discussion by prompting questions about why these objects have these common characteristics.
> 
> I'll turn this question around: Why should the proposed definition be used to define a "planet"? How does the consideration of simple roundedness advance scientific understanding? Why should slightly smaller asteroids and KBOs that aren't completely round be excluded? How are they fundamentally different from round things, in ways that point to scientifically interesting distinctions in composition, development, etc.?




There's your problem.  Categories aren't meant to advance discussions and prompt questions.  They are simply there as an organizational tool. Something that can be used to definitively distinguish one set from another.

You can still discuss and ask questions regardless of whether or not a method of classification encourages that or not...  A classification method will never prevent such discussion.

Consider the means of disguishing planets from other objects...

With regards to planets, the first stipulation writes itself: A planet must orbit a star.

After that, you need to set a minimum and maximum size.  Again, the upper limit write itself...  We already have definitions for stars, so if the object qualifies as a star, it's too big and is disqualified from being a planet.  The lower limit is the tricky point.  When you take a good look at planets and asteroids, the one fundemental break point in size is when an object has enough mass to make itself round...  So that's what they used.

Finally, there are a lot of moons that could technically fit this description, so you add a moon stipulation...  the common center of gravity.

Richard Binzel, a member of the Planet Definition Committee, said, "Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor. Nature decides whether or not an object is a planet."

Also realize that they will be creating sub-categories that support questions based on potential origins...

"The IAU draft Resolution also defines a new category of planet for official use: "pluton". Plutons are distinguished from classical planets in that they reside in orbits around the Sun that take longer than 200 years to complete (i.e. they orbit beyond Neptune). Plutons typically have orbits that are highly tilted with respect to the classical planets (technically referred to as a large orbital inclination). Plutons also typically have orbits that are far from being perfectly circular (technically referred to as having a large orbital eccentricity). *All of these distinguishing characteristics for plutons are scientifically interesting in that they suggest a different origin from the classical planets.*"


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## Zander (Aug 24, 2006)

*Official: Pluto no longer a planet*

According to this and other online reports, Pluto has been demoted.

Edit: Umbran, can you please merge this with Pbartender's thread? Thanks.  

Edit2: I'm not Umbran, but I play him on TV. Thread merged. _-Eridanis_


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## Umbran (Aug 24, 2006)

Well, Occam, you get your wish.

http://www.cnn.com/2006/TECH/space/08/24/pluto.ap/index.html

Futher reading on the new definition, though, is interesting.

"Planet" is still not based on details of formation or composition.  It is still basically a matter of size:

If it orbits the sun, is round, and is in a wide swath of cleared space, it is a planet.

If it orbits the sun, is round, but doesn't sit in cleared space (like Ceres and Pluto), it is a "dwarf planet".

Other bits that aren't round are "small solar system bodies".

So, basically, a planet is anything big enough to have swallowed up the debris in its orbit.


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## Pbartender (Aug 24, 2006)

I can dig that...  They're essentially using the same proposed rules, but added in, "and has cleared the neighborhood around its orbit."

Although, it seems that's not the reason Pluto was actually disqualified...  "Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's."

Also interesting to note that Ceres was considered a planet way back in the 1800's.


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## DaveMage (Aug 24, 2006)

Alas, poor Pluto.

For some reason, I feel very saddened by this...


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## BOZ (Aug 24, 2006)

i just thought that Pluto was a dog?


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## Acquana (Aug 24, 2006)




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## Zander (Aug 24, 2006)

BOZ said:
			
		

> i just thought that Pluto was a dog?



It is now.


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## kenobi65 (Aug 24, 2006)

BOZ said:
			
		

> i just thought that Pluto was a dog?




"There weren't gays when I was younger, Jody."

"Sure there were, Aunt Jessica.  They just weren't open about it.  There's been gays all through history.  Aristotle, Plato..."

"Plato?!?!  Mickey's dog was GAY??"


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## DaveMage (Aug 24, 2006)

kenobi65 said:
			
		

> "There weren't gays when I was younger, Jody."
> 
> "Sure there were, Aunt Jessica.  They just weren't open about it.  There's been gays all through history.  Aristotle, Plato..."
> 
> "Plato?!?!  Mickey's dog was GAY??"




Will Benson find out?

Will Benson care?


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## Harmon (Aug 24, 2006)

Ranger REG said:
			
		

> I might be subjected to a condition where my sex drive peaks once every seven years.




Might fit with most gamers chances at getting some.


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## occam (Aug 24, 2006)

Pbartender said:
			
		

> Categories aren't meant to advance discussions and prompt questions.  They are simply there as an organizational tool. Something that can be used to definitively distinguish one set from another.




I would argue that they're both. But I wanted ask something else: Based on what you've said here, it sounds as if it doesn't matter all that much to you what the ultimate decision is on the definition of a "planet", merely that there is one and that it's clear. Is that right? (A moot question, now, I guess.)


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## occam (Aug 24, 2006)

Umbran said:
			
		

> Well, Occam, you get your wish.
> 
> http://www.cnn.com/2006/TECH/space/08/24/pluto.ap/index.html
> 
> ...




And swallowing up the debris in its orbit is exactly what I was alluding to in comments about theorizing similar origins for all planets. I view that criterion as relating directly to formation processes.

In fact, I think that criterion would've been enough to separate planets out from other things. They could've left out the roundedness criterion and still had the same result. It would be a side effect that something big enough to have cleared out its orbit would've collected enough mass to become round. Still, until a non-round object that's cleared out its orbit is found in another star system (perhaps orbiting a brown dwarf? - in which case it'll be a long time before we can find one), I suppose it doesn't make much difference.


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## kenobi65 (Aug 25, 2006)

DaveMage said:
			
		

> Will Benson find out?
> 
> Will Benson care?




Someone got it! WOOT!!


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## Umbran (Aug 25, 2006)

occam said:
			
		

> And swallowing up the debris in its orbit is exactly what I was alluding to in comments about theorizing similar origins for all planets. I view that criterion as relating directly to formation processes.




I don't.  Whether the orbit is cleared depends on the size of the body, and density of material in the orbit, not the other details of the process by which the body was produced.  

Two bodies can form by the same process, but if by some accident one does not become large enough, it won't clear the orbit.  Similarly, if you happen to have a body that was bascially formed by a different process, it can clear an orbit that still contains clutter.  

And, of course, if you take a body formed by any process at all, and toss it into an area that was cleared by other means, it'll qualify as a planet.  And given collisions and close passes of unstable bodies in early solar systems, this is not a far-fetched possibility. 

Lastly - you talk a great deal about how differences of formation processes, when _we don't agree on what they are yet_.  Some suggest that the process by which Jupiter and large Kupier Belt objects form is the same - they simply happen in different places, with different particle densities and types available.


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## ph34r (Aug 25, 2006)

I can just imagine a parent trying to convince their kid that Pluto isn't a planet when they just learned it in school a few months ago. Could be an interesting conversation.


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## BOZ (Aug 25, 2006)

kenobi65 said:
			
		

> Someone got it! WOOT!!




Soap?


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## Angel Tarragon (Aug 25, 2006)

BOZ said:
			
		

> Soap?



Don't drop it.


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## DaveMage (Aug 25, 2006)

BOZ said:
			
		

> Soap?




Confused?  You won't be....


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## kenobi65 (Aug 25, 2006)

BOZ said:
			
		

> Soap?




Indeed.


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## crystal (Aug 25, 2006)

I will miss pluto, it was allways my fav.....


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## Templetroll (Aug 25, 2006)

k, so the solar system party now has a couple of dwarf planets in it!  It won't sell novels but to works for me!


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## Hypersmurf (Aug 26, 2006)

Pbartender said:
			
		

> I can dig that...  They're essentially using the same proposed rules, but added in, "and has cleared the neighborhood around its orbit."
> 
> Although, it seems that's not the reason Pluto was actually disqualified...  "Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's."




I'm puzzled.  If Pluto is disqualified because its orbit overlaps with Neptune's, why isn't Neptune disqualified since its orbit overlaps with Pluto's?

Isn't Neptune not-orbiting-in-a-swath-of-cleared-space, given Pluto's encroachment?

-Hyp.


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## Ranger REG (Aug 26, 2006)

Hypersmurf said:
			
		

> I'm puzzled.  If Pluto is disqualified because its orbit overlaps with Neptune's, why isn't Neptune disqualified since its orbit overlaps with Pluto's?
> 
> Isn't Neptune not-orbiting-in-a-swath-of-cleared-space, given Pluto's encroachment?
> 
> -Hyp.



Unlike the Bible and fairy tales, the giants always trump the little guys.


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## Umbran (Aug 26, 2006)

Hypersmurf said:
			
		

> I'm puzzled.  If Pluto is disqualified because its orbit overlaps with Neptune's, why isn't Neptune disqualified since its orbit overlaps with Pluto's?




No, despite Pbartender's quote, Pluto is disqualified by the definition, not because of the orbit overlap.  A number of folks at the IAU, much to my embarassment, gave less-than rational reasons for disqualifying Pluto and other similar objects ("ruining the magic" is not a rational scientific reason, guys!)



> Isn't Neptune not-orbiting-in-a-swath-of-cleared-space, given Pluto's encroachment?




No.  Because they don't _share_ orbital space.  Pluto occasionally comes nearer the Sun than Neptune, but theoir orbits don't actually cross in 3-space (because Pluto's orbit is eccentric and inclined with the ecliptic) - Pluto is never within the space you'd expect Neptune should clear.  Pluto's orbit does go back into the space we currently think of as being the Kupier Belt, which isn't clear.

Of course, if we ever find there's an empty gap between Pluto's orbit and hte rest of the KB, we have a planet again


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## dragonhead (Aug 30, 2006)

Apperently they will add xena as the 9th planet as pluto has be come a comet. its a shame because pluto had water on it. move it closer to the sun and vwa-la you have earth anew. i just feel sorry for the future when they see that our 9th planet is named after a tv show. the renameing of stuff to cosby city or republic of sinfeld will be interesting (and people wonder why the youth is dependent on tv)


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## Umbran (Aug 31, 2006)

dragonhead said:
			
		

> Apperently they will add xena as the 9th planet as pluto has be come a comet. its a shame because pluto had water on it. move it closer to the sun and vwa-la you have earth anew. i just feel sorry for the future when they see that our 9th planet is named after a tv show. the renameing of stuff to cosby city or republic of sinfeld will be interesting (and people wonder why the youth is dependent on tv)




Um, no.  "Xena" is an unofficial name, and it'll be changed when the IAU gets around to naming the thing.  It is of the same class of object as Pluto - a "Kupier Belt Object", or "pluton", rather than a comet.

And no, moving Pluto in would not result in Earth anew.  Pluto's small (smaller than our Moon), and a low enough density to guess that much of the mass is in frozen gasses, such that if you warmed it up, you'd not hold much of an atmosphere.


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## Aaron L (Sep 1, 2006)

Pbartender said:
			
		

> I'm rather hoping that they start naming all the new Kuiper Belt planets after Lovecraft's Great Old Ones...  Zhar and Lloigor would make a much better pair of outer planets than Xena and Gabrielle.






Dang that would be cool 


Planet Cthulhu!   


...planet Azathoth... or do Outer Gods count?


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## Aaron L (Sep 1, 2006)

Umbran said:
			
		

> Well, Occam, you get your wish.
> 
> http://www.cnn.com/2006/TECH/space/08/24/pluto.ap/index.html
> 
> ...





Ok, so now it goes...

My Very Educated Mother Just Served Us... 

Noodles... ?


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## paradox42 (Sep 1, 2006)

Aaron L said:
			
		

> Dang that would be cool
> 
> 
> Planet Cthulhu!
> ...



Eh, forget the deities themselves- if you go with Lovecraft, then you simply *must* name the outermost planet Yuggoth. 

Actually I remember reading a sci-fi/Cthulhu mythos story about the first human expedition to Yuggoth, with the most intriguing detail to my mind being that the story postulated that Yuggoth was a huge gas giant, even bigger than Jupiter IIRC. Current theories on the 'Planet X' that seems to be perturbing orbits out there in the Kuiper Belt and Oort Cloud suggest that it is indeed something (at least) that massive.


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