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Is Pluto a planet or plutoid? The debate continues...

Pluto is now officially classified as a plutoid, but astronomers are still unsure whether or not it should be considered a plutoid or planet.  One of the most popular debates among astronomers was yet again renewed during a conference at the Johns Hopkins University Applied Physics Laboratory at the end of last week.

The director of the American Museum of Natural History's Hayden Planetarium, Neil deGrasse Tyson, supports the official demotion of Pluto, while Mark Skyes, Planetary Science Institute director, believes Pluto should still be considered a planet.

After Pluto's discovery in 1930, the debate over its possible planetary status started immediately among astronomers and members of the media.  The 24-year old researcher who discovered the planet, Clyde Tombaugh, considered it the official ninth planet, while many others hailed Pluto's discovery, but said it wasn't a planet.

Since then, Pluto's status remains unclear, with astronomers continuing to flip flop over the plutoid.

The International Astronomical Union (IAU) officially demoted Pluto to a dwarf planet in 2006, only to classify it as something else just two years later.  The plutoid classification was created specifically for dwarf planets similar in size to Pluto.  Specifically, dwarf planets orbiting further than Neptune can be given the new classification, and must circle the sun and have their own gravitational field.

The IAU's specifications for a regular planet include the ability to orbit a sun, enough gravity to make it almost round, and have the power to send out objects that enter their orbit.  Some critics of Pluto's demotion believe any nonstellar object that is round and able to orbit a star should be considered an official planet.

Only Pluto and the dwarf planet of Eris currently carry the plutoid classification, although astronomers expect to add other planets in the future.  Skyes and company believe Earth's solar system should have 13 planets, when it only has eight.  Ceres, which is an object in an asteroid belt between Jupiter and Mars, would end up being the smallest planet in the solar system, if the system were put into place now.

Tyson would rather not count planets, but instead group bodies together when they have similar properties, even if this may further complicate things.

There are some astronomers who say Pluto should be considered a planet but everything else discovered moving forward should be considered a plutoid.  Even after the debate at JHU, Pluto remains in limbo, and will likely still be classified as a plutoid until astronomers are able to unanimously agree how it should be classified.

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Pluto is a Planet
By oab on 8/19/08, Rating: 0
RE: Pluto is a Planet
By FITCamaro on 8/19/2008 12:44:45 PM , Rating: 5
I just wanna know who's paying for all these discussions. It's almost like these scientists are like "Hey we're kinda out of work to do.....I KNOW! Lets continue to argue about Pluto and have someone pay us to do that!"

It would been a lot cheaper to just leave Pluto a planet and say everything else farther out than it was a really big f*ckin rock.


RE: Pluto is a Planet
By stirfry213 on 8/19/2008 12:58:44 PM , Rating: 4
This is like a whole bunch of geeks arguing whether Star Wars 5 or 6 was better.

Who cares! Call Pluto a planet and then classify everything else however you want and leave the damn thing alone. Its not like all the other plutoids are gonna say, "Why is Pluto a planet and not me? I wanna be planet! You are a celestial discriminator!"

/sarcasm


RE: Pluto is a Planet
By danrien on 8/19/2008 1:26:38 PM , Rating: 5
Star Wars 5 was better.


RE: Pluto is a Planet
By daftrok on 8/20/2008 4:28:59 AM , Rating: 2
Star Wars IV was better.


RE: Pluto is a Planet
By deeznuts on 8/19/2008 1:33:38 PM , Rating: 2
WTF is a star wars 5 or star wars 6?

There is only one Star Wars. Then the Empire Strikes Back, and finally Return of the Jedi.


RE: Pluto is a Planet
By stirfry213 on 8/19/2008 1:47:43 PM , Rating: 2
*smack head*

Why didn't I see this comment coming?


RE: Pluto is a Planet
By SiN on 8/19/2008 3:56:13 PM , Rating: 2
im sure you mean "smacks head" and not "smack head".

i'd of preffered it if you meant smack head though :D


RE: Pluto is a Planet
By erikejw on 8/19/08, Rating: -1
RE: Pluto is a Planet
By DOSGuy on 8/25/2008 2:41:20 AM , Rating: 1
I'm not an American and I think Pluto is a planet. Anything that's massive enough to be rounded by its own gravity -- but not massive enough to cause thermonuclear fusion -- that orbits the Sun is a planet. If that means that there are dozens of planets, so be it.

Those in favor of disqualifying Pluto often talk about how small it is. That's true: Pluto has half the radius of Mercury, the smallest planet. Of course, Mercury, Venus, Earth and Mars all have less than 1/10th the radius and 1/1000th the volume of Jupiter. Our planet is a "dwarf planet" compared to the gas giants -- Jupiter, Saturn, Uranus and Neptune. It's a pretty weak argument to say that Pluto isn't in the same class of celestial objects as Earth and Mercury, but Earth and Mercury are in the same class as Jupiter. We're much closer in size to Pluto than Jupiter. The inner planets of our Solar System are relatively tiny, and yet they're huge, massive objects. So is Pluto. It's a big huge world that is so massive that it has been rounded by its own gravity, and even captured three or more moons. Pluto is a planet.

The "dwarf planet" designation is an arbitrary and unnecessary designation designed to prevent newly discovered worlds that are a little bit smaller than Earth from being called planets, while keeping Earth in the same league as the comparatively huge gas giants. If Pluto is a dwarf planet, so are Mercury, Venus, Earth and Mars. There are big planets and small planets; terrestrial worlds and gas giants. You can sub-categorize them if you want, but at the end of the day, anything that's big and round and orbits the Sun is a planet.


RE: Pluto is a Planet
By FITCamaro on 8/19/2008 2:53:13 PM , Rating: 2
Star Wars IV wasn't Star Wars. It was A New Hope.


RE: Pluto is a Planet
By oab on 8/19/2008 3:18:05 PM , Rating: 1
It was called "Star Wars" no subtitle as the theatrical name when it was first launched, but the scrolling yellow text did call it "a new hope".


RE: Pluto is a Planet
By bribud on 8/19/08, Rating: 0
RE: Pluto is a Planet
By Seemonkeyscanfly on 8/19/2008 3:39:56 PM , Rating: 5
I believe Yoda, Obi-Wan and Luke would agree that Pluto is a small planet, but a planet all the same. I mean come on, they called it a death star – which was no bigger than a small moon. If that can be a star then Pluto can be a planet.

SW 6 rules over SW 5 - I just have one comment to that...Princess Leia Organa , barge, metal bikini - enough said.


RE: Pluto is a Planet
By HsiKai on 8/19/2008 6:09:10 PM , Rating: 2
quote:
I mean come on, they called it a death star – which was no bigger than a small moon.


I guess that's sarcasm, but on a more serious note, names for ships aren't the same as a classification of the ship. The Death Star could destroy planets just as Star Destroyers could, albeit requiring larger numbers. They both move about in space and shoot stuff while having a capacity to hold smaller ships/fighters/corvettes.

Officially, however, although it shares many of the same qualities as a Star Destroyer, the Death Star is a "space station."

As an aside, the second Death Star was anywhere from 50%-750% larger than the original. Definitely no moon.


RE: Pluto is a Planet
By lightfoot on 8/19/2008 6:12:01 PM , Rating: 2
Technically they are Star Wars Episodes 4, 5 and 6.

Empire and Jedi were technically "Star Wars Episode V: The Empire Stikes Back" and "Star Wars Episode VI: The Return of the Jedi".

You could argue that Episode 4 was "Star Wars" and not "A New Hope", because A New Hope was not in the title. But you cannot argue that Episode 5 and 6 were not "Star Wars" - they did have "Star Wars" in the title.

And for the record Star Wars geeks would never argue about that - Episode 5: The Empire Strikes back is by far the superior movie. Teddy bears can not overthrow the Empire. There can be no argument.


RE: Pluto is a Planet
By SiliconAddict on 8/19/08, Rating: -1
RE: Pluto is a Planet
By RIPPolaris on 8/19/2008 3:32:16 PM , Rating: 2
Empire had the better ending - Luke gets his hand cut off, finds out Vader is his father, Han gets frozen and taken away by Boba Fett - it ends on such a down note. That's what life is, a series of bad endings. All Jedi had was a bunch of Muppets.


RE: Pluto is a Planet
By Seemonkeyscanfly on 8/19/2008 3:49:00 PM , Rating: 2
Jim Henson and his muppets rule man. Any one who can stick his hand up Yoda's bottom and live to tell of another day has real power. Of course Jim Henson is dead now, maybe Yoda was not so happy after all.


RE: Pluto is a Planet
By bodar on 8/19/2008 6:01:28 PM , Rating: 2
Maybe he should've used quotes around that.

quote:
I'm not even supposed to BE here
-- Dante

Ring a bell now?


RE: Pluto is a Planet
By SiliconAddict on 8/19/2008 11:23:34 PM , Rating: 2
Damn it dude! I was going to see that movie this weekend. Thanks for ruining the ending..... ;-)


RE: Pluto is a Planet
By SiN on 8/19/2008 3:58:51 PM , Rating: 5
The Matrix was better off as a stand alone movie!!


RE: Pluto is a Planet
By Seemonkeyscanfly on 8/19/2008 4:37:27 PM , Rating: 2
ahhh NO.

Matrix is good, but no, not even close. You have to remember near 20 years of technology changes between Star Wars IV and Matrix.


RE: Pluto is a Planet
By HsiKai on 8/19/08, Rating: -1
RE: Pluto is a Planet
By atwood7fan on 8/19/2008 8:26:55 PM , Rating: 2
The ability to classify a planet is insignificant next to the power of the FORCE


RE: Pluto is a Planet
By Cygni on 8/19/2008 1:05:46 PM , Rating: 4
What, exactly, do you think professors do with their spare time? They nerd out and argue. Frankly, outside of teaching and research, its their JOB to stay current in their field.


RE: Pluto is a Planet
By PointlesS on 8/19/2008 4:48:16 PM , Rating: 2
it's my job to stay current in my field too but I don't go to conferences to debate that a mac should technically be classified as a pc


RE: Pluto is a Planet
By HsiKai on 8/19/2008 6:00:59 PM , Rating: 3
That's because technically they are PCs. http://en.wikipedia.org/wiki/Macintosh

I would argue that they aren't, simply based on the ability to customize a unix/linux/MS platform compared to a Mac (though I understand the importance of having a standardized hardware set to program to).

A better analogy would be classification of viruses, worms, trojans, etc. That can be harder to do, but consumers use the generalization that "anti-virus" software protects them from all of those security risks.


RE: Pluto is a Planet
By lightfoot on 8/19/2008 6:05:20 PM , Rating: 4
quote:
..a mac should technically be classified as a pc


Technically so too should an Xbox, a PS3, and your cell phone. They all do personal computing and thus should be considered "personal computers."


RE: Pluto is a Planet
By maven81 on 8/19/2008 2:30:45 PM , Rating: 5
Hate to break it to you, but before we had decent enough telescopes and enough observations some astronomers called what we now term a galaxy a "spiral nebula".
Imagine if we followed your thinking on that one... "yeah, so a galaxy is not a nebula at all, but hey, we've already named them, changing names is stupid and a waste of time"
That's not how science works. If you find that the old ideas were incorrect, you change them, you don't stick to them for old times sake.
Eris is larger then Pluto, so to say that Pluto should be a planet, while Eris can't be is arbitrary and weird. Either we keep adding planets (and there could be dozens) or try to classify things more precisely.
The problem is that so far the definitions they've come up with are pretty dumb. Some don't even function outside the solar system!


RE: Pluto is a Planet
By FITCamaro on 8/19/08, Rating: 0
RE: Pluto is a Planet
By masher2 (blog) on 8/19/2008 3:23:28 PM , Rating: 5
> "Anything farther out than Pluto that doesn't orbit another planet isn't a planet"

So if it *does* orbit another planet, it's a planet itself? What about objects that spend 95% of their time further out than Pluto, but dip in briefly on a very highly elliptical orbit? What if we discovered an object further out that orbits the sun, and is as large as the Earth?

Classification is a bit more difficult than you might think.


RE: Pluto is a Planet
By Seemonkeyscanfly on 8/19/2008 3:56:35 PM , Rating: 2
When they are inside Pluto orbit then they are a planet, out side of Pluto's orbit then they are no longer a planet.
This will make taking test much more fun. The number of planet could go up or down and any given moment. :)

Really I do not see the big deal, so what if we have 8 planets or 38 planets. Yes, have a standard to meet first but if it is there and meets the standard then count it. Since Pluto is the smallest "planet" then that can be are minimum standard.


RE: Pluto is a Planet
By Some1ne on 8/19/2008 6:50:18 PM , Rating: 2
quote:
What about objects that spend 95% of their time further out than Pluto, but dip in briefly on a very highly elliptical orbit?


Now you're just being silly. For the purposes of classification, the distance from the sun to an object orbiting it is always equal to the apogee of the object's orbit. It doesn't matter how elliptical the orbit may be, or how close the object may pass to the sun. If its apogee is greater than Pluto's apogee, then it is further from the sun than Pluto is, as far as classification is concerned.

The object's instantaneous distance from the sun only really matters if you're planning to send a probe/expedition to it.


RE: Pluto is a Planet
By boogle on 8/19/2008 4:54:57 PM , Rating: 2
Doesn't orbit another planet? Eh? If the body is small enough, that would be a moon...

Either way, pluto has too big a sentimental value. Astronomy needs to be neutral, and not specific to our solar system. I agree with what others have said, we need specific classification for orbiting bodies. Just because something is very far from a star - if its orbiting it and its big enough, it should be a de facto planet. If its too small, but not an asteroid then it needs some other classification.

Maybe a grading of 'planets', say Type A, Type B, Type C, etc. With the type specifying things like size, composition, and distance from the local star.

Plutoid is a stupid name. Thats like calling all planets that can sustain life 'Earthoids'. Personally I'm not really sure you can call Pluto a de facto planet since its smaller than Ganymede. I quite like the term dwarf planet though, albeit maybe replacing 'planet' with some other name to avoid confusion. Rogue moon? :p


RE: Pluto is a Planet
By acer905 on 8/19/2008 5:26:37 PM , Rating: 2
If you wan to have a grading scale for the planets, look no further than the Star Trek universe. Class M all the way!

http://en.wikipedia.org/wiki/Star_Trek_planet_clas...


RE: Pluto is a Planet
By HsiKai on 8/19/2008 5:51:12 PM , Rating: 2
"That's no moon. It's a space station."

quote:
Maybe a grading of 'planets', say Type A, Type B, Type C, etc. With the type specifying things like size, composition, and distance from the local star.


That would leave a lot of types. Look at the classifications of stars, at least all those things have one major thing in common: fusion at some point in it's life. Even planets aren't that straight forward.

quote:
Plutoid is a stupid name. Thats like calling all planets that can sustain life 'Earthoids'.


That would make sense if "Earth" were Latin like Pluto, but it's not. Thus it doesn't apply to Latin naming conventions as Pluto does. We do call ourselves "Terrans" as that is the Latin form; terra meaning earth (notice the capitalization).


RE: Pluto is a Planet
By das mod on 8/19/2008 12:54:59 PM , Rating: 4
initially it was demoted as planet because of it's size,
which would be the equivalent to demoting midgets, as people.


RE: Pluto is a Planet
By 4play on 8/19/2008 1:56:33 PM , Rating: 2
Pluto should take the case to court!


RE: Pluto is a Planet
By Oregonian2 on 8/19/2008 2:43:08 PM , Rating: 2
Because it's being called a midget?


RE: Pluto is a Planet
By lightfoot on 8/19/2008 6:17:44 PM , Rating: 2
They prefer to be called "dwarf planets."


RE: Pluto is a Planet
By FITCamaro on 8/19/2008 2:55:14 PM , Rating: 4
It couldn't see over the bench.


RE: Pluto is a Planet
By nosfe on 8/19/2008 12:58:03 PM , Rating: 3
plutoid? then what would be next? Australia will become an austrailioid instead of a continent, we can't let this blasphemy continue!


RE: Pluto is a Planet
By Bender 123 on 8/19/2008 1:37:34 PM , Rating: 2
Austranent?

Sounds cool,lets do that...and monetize it!


RE: Pluto is a Planet
By psychobriggsy on 8/19/2008 1:05:26 PM , Rating: 3
The historical argument is the most non-scientific.

Considering that they are trying to come up with a scientific definition of a planet, that isn't a good idea.

The fact is that Pluto is a ball of icy gravel that hasn't cleared its orbit of other icy gravel objects, and its orbit is so eccentric that it is a clear outlier from the obvious 8 planets (4 rocky planets and 4 gas giant planets) that we have.

I agree with the "near spherical under own gravity" definition, and the "orbits a sun" definition.

Other definitions (orbit must be non-eccentric has issues with 'where is the cut-off point') have issues.

Personally I would actually have plutoids defined as planets, as long as they're spherical under their own gravity, and orbit the sun. It does mean that we could end up with dozens of planets in the solar system, but so what!


RE: Pluto is a Planet
By arazok on 8/19/2008 1:38:24 PM , Rating: 2
I can see the logic in both sides arguments, so I have a tough time deciding where to land on this one.

Clearly, this calls for a rock, paper, scissors based decision. I would also respect the outcome of a thumb war.


RE: Pluto is a Planet
By Rookierookie on 8/19/2008 1:41:51 PM , Rating: 2
There was a time when people couldn't tell the difference between Venus and the stars.

And humans discovered a lot of the stars a LONG time ago.


RE: Pluto is a Planet
By FITCamaro on 8/19/2008 2:56:54 PM , Rating: 1
Looking up is hardly a discovery.


RE: Pluto is a Planet
By Ratinator on 8/19/2008 2:19:47 PM , Rating: 3
Keep the consistency for crying out loud and stop having this pointless debate. Pluto was properly demoted to a plutoid and now gets it's recognition through name. You are not diminishing the discovery of anyone, only properly categorizing a body of that size. Nothing changes the fact that Clyde discovered it. Stop the nonsense and end this pitiful debate for once and for all. It is a complete waste of money.


Absolutely embarrassing
By fishbits on 8/19/2008 1:01:39 PM , Rating: 3
Seriously, this is embarrassing. Pluto's status was determined over 70 years ago, leave it the hell alone. Come up with a standard that will apply to all bodies beyond the current 9.

If anyone wanted an excuse to cut/deny increases to astronomy funding, a bunch of nerds with nothing more pressing to attend to than a taxonomical slapfight makes the case for them. Way to pointlessly piss away public good will over something that will benefit no one.

Take Pluto out of the equation, and nobody will lose sleep over the classifications they come up with. Then this will be done and over with that much faster, and these petulant pedants can hopefully get some useful work done.




RE: Absolutely embarrassing
By 4play on 8/19/2008 1:54:49 PM , Rating: 3
You know what's embarrassing? Having so many people emotionally attached to a celestial body that is so far and so small. Scientist are trying to come up with a definition to categorize future planets, unfortunately Pluto doesn't fit it.

This is science people! Just because we were taught incorrectly in school doesn't mean we should keep it that way. Emotions really have no place when it comes to science.


RE: Absolutely embarrassing
By Digimonkey on 8/19/2008 2:37:58 PM , Rating: 2
I concur. I say if we have the technology let's just blow Pluto up and be done with it. That way we can move on.


RE: Absolutely embarrassing
By FITCamaro on 8/19/2008 3:00:19 PM , Rating: 1
Blowing something up makes everyone feel good. :)


RE: Absolutely embarrassing
By Ctsephion on 8/19/2008 5:18:50 PM , Rating: 5
that the excuse you make when you take out your doll? ;)


RE: Absolutely embarrassing
By HsiKai on 8/19/2008 5:30:17 PM , Rating: 2
Haha, this deserves a 6!


RE: Absolutely embarrassing
By HsiKai on 8/19/2008 5:29:48 PM , Rating: 2
Only on MythBusters.


RE: Absolutely embarrassing
By Solandri on 8/19/2008 4:46:38 PM , Rating: 4
quote:
Seriously, this is embarrassing. Pluto's status was determined over 70 years ago, leave it the hell alone.

Part of the problem is that Pluto was hailed as the 9th planet under false pretenses. After Neptune's discovery, astronomers did calculations on the motions of the known planets, and found there was still a discrepancy. Based on that discrepancy, they calculated the size (gravity) and location of a 9th planet. Based on that calculated location, Tombaugh was searching that specific section of sky when he found Pluto. It was too far to accurately measure its size, but it was in the right place at the right time so everyone figured it was the 9th planet.

As more accurate measurements of Pluto's size came in, astronomers realized it simply didn't have enough mass to account for the perturbations they were seeing in the orbits of the other planets. There was still something (or many things) out there affecting the orbits of the planets. If they'd known this at the time, Pluto probably never would've been classified as a planet in the first place.


RE: Absolutely embarrassing
By HsiKai on 8/19/2008 6:12:37 PM , Rating: 2
Precisely; if only they taught this stuff in schools (outside of the lowly Earth Science).


Pluto is a comet
By lightfoot on 8/19/2008 6:25:44 PM , Rating: 1
Pluto is an icy body (not a rocky body) and should be considered a comet; not a planet, dwarf planet, or plutoid.




RE: Pluto is a comet
By HsiKai on 8/19/2008 6:39:30 PM , Rating: 2
No, for several reasons.

1. Pluto has satellites, one of which is larger than Pluto itself. http://en.wikipedia.org/wiki/Pluto%27s_natural_sat...
2. Pluto does not leave a trail of debris behind it giving it a "tail" at any part of it's orbit around the sun. http://en.wikipedia.org/wiki/Comet
3. Pluto does not meet the size requirements of a comet.
4. Pluto is not "an icy body." http://en.wikipedia.org/wiki/Pluto
From wiki:
"Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small..."
5. Pluto has changed it's shape (becoming more spherical) due to its own gravity. "More explicitly, it has to have sufficient mass for its self-gravity to overcome rigid body forces in order to assume a hydrostatic equilibrium and acquire a near-spherical shape." http://en.wikipedia.org/wiki/Dwarf_planet


RE: Pluto is a comet
By lightfoot on 8/20/2008 1:26:24 AM , Rating: 2
I made the statement in half jest, but let me address your "reasons."

1. Pluto has satellites - so what? A satellite does not define the object that it orbits.
2. Pluto does not have a "tail" - but it's surface does "evaporate" when it's closest to the sun (perigee) and refreezes as it nears its apogee - just because we can't see the tail does not mean it does not exist.
3. Pluto does not meet the size requirements of a comet - there is no upper bound on the size of a comet, and it is definitely not too small.
4. Pluto is not "an icy body." Recheck your source. "Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice." Using your link to the definition of a comet - "Short-period comets are thought to originate in the Kuiper Belt, or associated scattered disc." The composition of Pluto should be quite similar to other Kuiper Belt objects, i.e. comets.
5. Pluto is spherical. Can comets not have sufficient mass to become spherical?

I'd be happy to hear any more of your so-called "reasons" that Pluto is not a comet. I will admit that Pluto's orbit is not nearly as "elongated" as traditional comets, but it "is markedly different from those of the planets."


RE: Pluto is a comet
By HsiKai on 8/20/2008 2:38:24 AM , Rating: 2
quote:
A satellite does not define the object that it orbits.


By definition of it's mass, and thus gravity, the object in question defines what orbits it. A variety of asteroids are capable of [noticeably] affecting other objects within their gravitational field and may have satellites (http://en.wikipedia.org/wiki/Asteroid_moon ). Of the large asteroids Ceres and Eris are actually classified as a "dwarf planets," like Pluto (see: http://en.wikipedia.org/wiki/Ceres_(dwarf_planet) ). Eris even officially has a large moon.

Turning the definition around, if a planet or asteroid (of any type) can have moons, then only moons can have planets and asteroids. Comets don't seem to have moons, nor do comets orbit celestial bodies other than the sun. In the case of Pluto, it is generally considered a binary system with Charon, so I don't think that a binary dwarf planet system, in addition to Pluto's other moons, would be "pass[ing] through the inner Solar System" on their orbit around the Sun (see the second paragraph: http://en.wikipedia.org/wiki/Comet ).

Pluto also has a nearly regular orbit (though an odd angle/shape), which is to say it has been observed traveling along the same path around the sun for quite a while. Just like, gasp, the other "planets!"

Now, you could argue that because Pluto seems to be from the Kuiper Belt that it has a history of asteroid-like behavior, which would be true, since it's a KBO and acts like an asteroid, just a really big one.

quote:
but it's surface does "evaporate" when it's closest to the sun (perigee) and refreezes as it nears its apogee - just because we can't see the tail does not mean it does not exist.


Yes, if you bring Pluto close enough to the Sun all of that ice (and the solar wind blowing on it) would give it a tail. Its distance from the Sun, orbit, and placement in the Kuiper Belt, make it more asteroid-like and, due to it's size, more planet like, than a comet (again, see the wiki on comets/Pluto).

quote:
there is no upper bound on the size of a comet, and it is definitely not too small.


No, but large objects tend to get stuck in this elliptical orbit and revolve around the Sun, versus passing in and out of the inner Solar System and having an odd orbit only to eventually use the Sun's gravity to sling-shot away, out of the Solar System forever.

quote:
The composition of Pluto should be quite similar to other Kuiper Belt objects, i.e. comets.

Outside of the Kuiper Belt "cold outer reaches of the Solar System where ices remain solid and comet-like bodies are not expected to exhibit much cometary activity" that is true. But bodies that exhibit comet-like behavior aren't just sitting around like Pluto is. For example, it seems to meet the first two of these criteria according to the IAU:
quote:
1. The object must be in orbit around the Sun.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
3. It must have cleared the neighbourhood around its orbit.


So Pluto could have been knocked out of the Kuiper Belt and exhibited slight comet-like behavior, but was so massive that it actually shaped itself. Comet's can't do this and after burning all of their ice off become asteroids.

(Actually I believe the opening to Voyager had an asteroid (formerly a comet) hurling through space and would be a prime example of a comet-turned asteroid.)

quote:
Can comets not have sufficient mass to become spherical?


No, they can't. Wiki says it has to do with hydro-static equilibrium: http://en.wikipedia.org/wiki/Hydrostatic_equilibri...

This is probably your best bet for understanding why the classification of Pluto is going on and why it's either a planet or dwarf planet:
1. http://en.wikipedia.org/wiki/Asteroid#Classificati...
2. http://en.wikipedia.org/wiki/2006_definition_of_pl...


RE: Pluto is a comet
By nycromes on 8/20/2008 9:31:58 AM , Rating: 2
Though I don't care to address everything in your post, one simple error in logic exists in the following statement:

"Turning the definition around, if a planet or asteroid (of any type) can have moons, then only moons can have planets and asteroids."

To go back to basic logic, please reference if then implication statments in logic:
If P then Q does not imply If Q then P. Therefore, your turning around of the definition does not apply.

I believe one point that can be drawn from the arguement that pluto is a comet is that our current definitions of astrological bodies are too vague and an arguement can be made for some objects to fit into multiple catagories. Pluto especially as it currently could be argued to be any one of multiple objects (large asteroid, comet, planet, plotoid, etc).


RE: Pluto is a comet
By lightfoot on 8/20/2008 11:45:00 AM , Rating: 2
quote:
A variety of asteroids are capable of [noticeably] affecting other objects within their gravitational field and may have satellites

Most objects in space have natural satellites. It is a function of the objects mass (the fact that it has it, not the magnitude.) As you stated some asteroids have moons and these asteroids are called Dwarf Planets, but they are still asteroids.

quote:
No, but large objects tend to get stuck in this elliptical orbit and revolve around the Sun, versus passing in and out of the inner Solar System and having an odd orbit only to eventually use the Sun's gravity to sling-shot away, out of the Solar System forever.

That's odd; all objects, regardless of mass, tend to get stuck in an "elliptical orbit." It has something to do with physics, but I'll spare you the details.

You might also want to look up "Halley's Comet" - it has an elliptical orbit with a period of approximately 76 years. It may eventually lose its tail, or collide with another body, but it will never "slingshot" out of the solar system as you imply comets do.

In any case your argument seems to center around Pluto being a dwarf planet. This I do not deny, however it does share more characteristics of a comet than a planet.


RE: Pluto is a comet
By HsiKai on 8/20/2008 1:11:19 PM , Rating: 2
quote:
...they are still asteroids.


And asteroids are either fragments of a destroyed planet; excess fragments of mass that was used to create planets; or dead comets, but those asteroids would have highly elliptical orbits.

quote:
You might also want to look up "Halley's Comet" - it has an elliptical orbit with a period of approximately 76 years. It may eventually lose its tail, or collide with another body, but it will never "slingshot" out of the solar system as you imply comets do.


You're right, if it doesn't sling-shot out of the Solar System it could crash into the Sun. :) In other unlikely news here's a picture of the orbit, with two other comets for comparison:

http://en.wikipedia.org/wiki/Image:Orbits_of_perio...

Larger masses tend not to sling-shot out of the Solar System like comets, although they're all moving outwards. They do not have "highly elliptical orbits."

quote:
...comet than a planet.


It seems more like an asteroid to me, but due to it's size the term "dwarf planet" doesn't bother me. It has to do with physics, but I'll spare you the details.


RE: Pluto is a comet
By theapparition on 8/20/2008 10:18:40 AM , Rating: 2
quote:
1. Pluto has satellites, one of which is larger than Pluto itself.

Charon (Pluto's largest of 3 satellites) is by no means larger than Pluto.

You perhaps got it mixed up that Charon is the largest moon, propotionally, to any planet in the solar system. So large, in fact that the center of revolution is outside of Pluto's surface.


Planet vs. !Planet Fallacy
By MozeeToby on 8/19/2008 1:15:27 PM , Rating: 1
Saying that everything we see in the cosmos must either be a planet or not a planet is a false delimma. The cosmos don't divide every phenomenon into neat categories that are easy to count and define. There are millions of objects just within our own solar system and trillions of trillions of objects outside it, there will always be some that skirt the definitions we come up with, no matter how precise that definition is.

When the planets were first discovered, we simply called them planets, because we didn't know enough to differentiate them. Then we devided them between gas giants, and terrestrial worlds because we learned how incredibly different the two classes are. If planets were only discovered today, do you really think that scientists would put the same label on gas giants as terrestrial worlds?

The label "Planet" is nothing more than that, a label and an old, outdated one at that. There is a huge range of objects in space, there will always be overlap and gaps in any labels that we come up with. It doesn't matter what word we use to describe them, the words will always be inadequate to understand the enormous variety the universe offers us.




RE: Planet vs. !Planet Fallacy
By AssBall on 8/19/2008 1:48:39 PM , Rating: 1
I see what you are saying, to an extent.

The idea is to categorize these objects more specifically. This "kinda round" and "has gravity" definition is too vague.

Here is what american Heritage Dictionary says:
A large celestial body, smaller than a star but larger than an asteroid, that does not produce its own light but is illuminated by light from the star around which it revolves.

This is also vague. It would not be hard to make the standard definition concretely quantitive with somethign along the lines of the following:

1: Has to be within a maximum radius of a star (this radius could vary on how massive the star is).
2: Has to exceed a set minimum mass.
3: Must fall within a maximum degree of eccentricity in its orbit.

Use any criterion you want to agree on for that matter. If they just made up some sensical rules as to how planet is defined, wouldn't this leave no room for arguments? It either fits the definition exactly or does not, period.

/2¢


RE: Planet vs. !Planet Fallacy
By DanoruX on 8/19/2008 2:05:37 PM , Rating: 2
How about any object orbiting a star (and not an object that in turn is orbiting one) that has a surface gravity of at least 0.Xg...


RE: Planet vs. !Planet Fallacy
By MozeeToby on 8/19/2008 3:01:52 PM , Rating: 2
Few questions...

What about Double Planets orbiting each other?
What constitutes the 'surface', the top of the atmosphere or the rocky surface? What if there isn't a rocky surface/atmosphere?

Gravity at the surface is in large part a question of density rather than mass. The surface gravity of Suturn is only .9g despite it's being many times more massive than the Earth.


RE: Planet vs. !Planet Fallacy
By MozeeToby on 8/19/2008 2:09:41 PM , Rating: 2
The problem is there will always be exceptions.

For mass, moons could be included just as easily as planets (and who ever decided they shouldn't be included?). If you try to exclude moons based on their orbit, you usually accidentally exclude double planets (two nearly equal massed object in orbit around their center of mass). Ironically, if you try to further amend the rules to permit double planets you often are forced to count the earth/moon system as a double planet and always have to include pluto/charon as a double.

As for distance, that could vary wildly depending on how the system formed, something we don't know much about yet. Until extra solar planets were discovered, hot jupiters were thought to be impossible, so who's to say that the other extremem isn't possible as well.

For eccentricity, that seems to be a good idea except when something strange happens. Look at Uranus, the only planet in our solar system with poles that point along the ecleptic. What if a near miss early in a solar systems formation sends one or two planets on widely eccentric orbits?


RE: Planet vs. !Planet Fallacy
By surt on 8/19/2008 2:11:42 PM , Rating: 3
Here is the definition astronomers have adopted:
http://en.wikipedia.org/wiki/2006_definition_of_pl...

The 2006 definition of "planet" by the International Astronomical Union (IAU) states that in the solar system a planet is a celestial body that: (1) is in orbit around the Sun, (2) has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and (3) has "cleared the neighbourhood" around its orbit.

The problem is that everyone except for astronomers (and nearly half of astronomers) want to drop #3 from the definition. The downside would be forcing millions of schoolchildren to memorize many more planets (13 and counting in our solar system).


RE: Planet vs. !Planet Fallacy
By Oregonian2 on 8/19/2008 2:49:36 PM , Rating: 2
They had to be memorized? Let's see... Jasoom, Barsoom, ... I forget the rest..

Name them by number with one or more letter suffixes that designates details: 1S, 2S, 3E + 3aM, .... kids just have to memorized the number parts. Piece of cake...


Does it really matter?
By DanoruX on 8/19/2008 12:49:49 PM , Rating: 2
Seriously, the only things we should be concerned about are habitability and economic viability of any objects in space. "Planet" and "plutoid" are all semantic drama, nothing more...




RE: Does it really matter?
By Icelight on 8/19/2008 1:55:44 PM , Rating: 2
No way! I'm not livin' on no Plutoid!

Planet lovers represent!


RE: Does it really matter?
By Oregonian2 on 8/19/2008 2:55:54 PM , Rating: 2
All jokes aside, there's good reasons to come up and consistently use verbiage definitions so that when someone says something others will know what was meant. When talking about spotting planets or types of planets in other star systems.. one will have to qualify what one means every time the word "planet" is used. Would get old quick. Definitions need to be stable and sufficiently detailed for use -- which may be more than newspaper use (perhaps the only thing where "planet" is sufficient -- perhaps astronomers should jettison the word except for when talking to the press).


These guys shouldn't be astronomers...
By DeepBlue1975 on 8/19/2008 1:20:24 PM , Rating: 2
But rather language analysts!

Instead of keeping up the research they just debate over stupid semantics. What's worse, these semantics are completely ad hoc, as they made them up by themselves, and for themselves.

Really a big waste of time, and maybe even money.




RE: These guys shouldn't be astronomers...
By boogle on 8/19/2008 5:13:38 PM , Rating: 2
That's like saying 'Well a hexagon is really just a pentagon, splitting them up is semantics. Just call them polygons and be done with it.'.

To put this into tech perspective, imagine if instead of naming the instruction sets for CPUs, we just labelled them 'instructions' to avoid semantics. You wouldn't know whether a CPU worked with Windows (aka x86) or not. Or if instead of specifying RAM/HD/Cache, we just called it 'Memory'. So in a PC spec you see '8196MB Memory'. How big is the HD? How much RAM is there? How much cache is there?

Its important that celestial bodies have specific names and classifications. Admitidly it's not absolutely critical right now - but if we ever start really exploring the solar system it will be.


By DeepBlue1975 on 8/19/2008 5:55:44 PM , Rating: 2
Pluto already had a classification. Which then was changed... Now to be debated again.

That's what pisses me off. They should just test Pluto's status against the already existent definition of planet, and if it fits, then call it a planet, if it doesn't, well, don't call it a planet and find the closest classification it'll fit and stick Pluto's to that one.


Here's how I look at it
By Shadowself on 8/19/2008 2:35:34 PM , Rating: 3
If it orbits a star and has an atmosphere it's a planet. If it does not do both, it's not a planet.

Mercury has an atmosphere (barely, but it's there)=> Planet.
Venus has an atmosphere => Planet.
Earth has an atmosphere => Planet.
Mars has an atmosphere => Planet.
Ceres does not have an atmosphere => not a Planet.
Jupiter has an atmosphere => Planet.
Saturn has an atmosphere => Planet.
Uranus has an atmosphere => Planet.
Neptune has an atmosphere => Planet.
Pluto has an atmosphere at least over a significant fraction of its orbit => Planet.




RE: Here's how I look at it
By MozeeToby on 8/19/2008 3:04:54 PM , Rating: 1
quote:
Pluto has an atmosphere at least over a significant fraction of its orbit => Planet.


So do comets.


Pluto is a dog
By VoodooChicken on 8/19/2008 2:48:39 PM , Rating: 3
A cartoon dog. Not even an anthropomorphic dog, just a dog. Owned by a cartoon anthropomorphic mouse.




Cage Deathmatch
By jskirwin on 8/19/2008 2:55:17 PM , Rating: 2
I think that both sides of the debate should pick small teams to represent them; then they could settle the issue once for all in a cage deathmatch.




Gravitational Field
By Divineburner on 8/20/2008 2:01:29 AM , Rating: 2
quote:
and have their own gravitational field.


..May I ask? Is there anything in the Solar System that does not have their own gravitataional field?




Once a planet, always a planet!
By pjs on 8/20/2008 11:37:08 AM , Rating: 2
"International Astronomical Union (IAU) officially demoted Pluto to a dwarf planet in 2006, only to classify it as something else just two years later. "

I have decided to demote the IAU to irrelevancy. Where do these people get off telling us that pluto is a planet one day, a dwarf planet another day and a plutoid or whatever the term du jour is today. Don't they have any real work to do or are they merely over-funded?

Pluto planet rocks!




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