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Pluto Demoted


oDDity

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Here you go then:

 

http://www.abc.net.au/science/news/stories...40687.htm?space

http://www.abc.net.au/science/news/stories...19677.htm?space

http://www.abc.net.au/science/news/stories...96218.htm?space

http://www.newscientistspace.com/article.n...line-news_rss20

http://www.newscientist.com/article.ns?id=...line-news_rss20

 

 

And here is a very pertinent link:

http://news.bbc.co.uk/2/hi/science/nature/5283956.stm

 

"Dr Alan Stern, who leads the US space agency's New Horizons mission to Pluto and did not vote in Prague, told BBC News: "It's an awful definition; it's sloppy science and it would never pass peer review - for two reasons.

 

Pluto discoverer Clyde Tombaugh pictured in 1980 (AP)

Pluto was discovered in 1930 by the American Clyde Tombaugh

"Firstly, it is impossible and contrived to put a dividing line between dwarf planets and planets. It's as if we declared people not people for some arbitrary reason, like 'they tend to live in groups'.

 

"Secondly, the actual definition is even worse, because it's inconsistent."

 

One of the three criteria for planethood states that a planet must have "cleared the neighbourhood around its orbit". The largest objects in the Solar System will either collect together material in their path or fling it out of the way with a gravitational swipe.

 

Pluto was disqualified because its highly elliptical orbit overlaps with that of Neptune.

 

But Dr Stern pointed out that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path.

 

These rocks are all essentially chunks of rubble left over from the formation of the Solar System more than four billion years ago.

 

"If Neptune had cleared its zone, Pluto wouldn't be there," he added.

 

Stern said like-minded astronomers had begun a petition to get Pluto reinstated. Car bumper stickers compelling motorists to "Honk if Pluto is still a planet" have gone on sale over the internet and e-mails circulating about the decision have been describing the IAU as the "Irrelevant Astronomical Union". "

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oDDity:

 

The material an object is made of is irrelevant to wether or not you classify it as a planet.

 

Temperature is irrelevant.

 

 

Interesting that you think shape is relevant but nothing else is, just because that's how you happen to want it to be.

 

That depends on your definition, and there are a few floating around. Many astronomers would classify Jupiter as a Brown Dwarf for the simple reason that it emits more energy than it receives form the Sun.

Some astronomers may call Jupiter a brown drawf, but the official definition is 12 jupiter masses. Again, you'll use the fact that 'some astronomers' call jupiter a brown dwarf to try and back uo your own erroneous view, while dismissing the fact that some other astonomoers believe pluto not to be a planet, becasue you dont' agree with that.

Pathetic.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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While I agree with the idea of calling anything with enough mass to be spheroid a planet, I don't see why orbits and behavior and such can't be taken into account for scientific terminology; how else do you define a "moon" or "satellite"? (surely those are useful scientific terms) And I don't see anything wrong with taking into account the material something is made of, the way terms like "gas giant" do.

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Who would describe the worlds largest body of professional astronomers and related fields as irrelevant?

 

 

Apparently quite a few professional astronomers (and quite probably a majority - the IAU vote was cast by a small majority of 400 or so astronomers, which is hardly representative of the wider opinion of astronomers) - see the link in one of my previous posts.

 

oDDity:

 

"interesting that you think shape is relevant but nothing else is, just because that's how you happen to want it to be."

 

Shape as a result of self-gravity is relevant becasue it is a consistent and scientifically definable way of classifying something. Since an object's temperature will vary immensly depending on its location, age and other variable which are highly mutable, it is a poor choice for classifying an object. Stellar objects can move around a lot. You don't like things made of ice being called planets, but what about liquid water? A gaseous planet of water vapour?

 

You could use material to classify something as being a planet, but again, you run into problems if you are not careful. Jupiter is made primarily of hydrogen gas, and we call it a planet. Venus is made of rock with a thick atmosphere of carbon dioxide. And most planets are made of a number of materials in layers, so your definition could end up being quite complicated if you base it on material. And you would have to be careful not to be too arbitrary here - excluding water ice out of all the materials planets can be made of makes no sense at all.

 

I could just as arbitrarily say that becasue Jupiter is not made primarily of rock, it isn't a planet.

 

As you may have gathered, I am not too impressed with the way the IAU has been officially defining things, as they are using highly arbitrary and unscientific definitions for things, which as a scientist, irritates me no end. You would never get away with that in any other scientific field. And there are a substatial number of professional astronomers who would agree with me (the IAU vote on the definition of planets was very close, and was not really representative of the wider astronomical community).

 

 

oDDity: "Hang on though, any drop of liquid becomes spherical in space, regardless of its mass, so obviously the material is relevant."

 

No, a drop of liquid can assume a spherical shape due to surface tension, not self-gravity. Actually, any drop of liquid will do this to one degree or another, and they form a blob that wobbles around, and is not consistently spherical. So should we exclude all planets in a liquid state?

 

 

Gildoran: "While I agree with the idea of calling anything with enough mass to be spheroid a planet, I don't see why orbits and behavior and such can't be taken into account for scientific terminology; how else do you define a "moon" or "satellite"? (surely those are useful scientific terms) And I don't see anything wrong with taking into account the material something is made of, the way terms like "gas giant" do."

 

Sure, but the term "planet" should be the base category, upon which things can be subcategorised. "planet" means "wanderer" in Greek, and is quite appropriate for things floating around in space. Personally, I would classify moons as planets where they fit my definition, and calling them moons or satellites would simply be a descriptor of their current location.

 

 

If say, Ganymede or Titan happened to be orbiting on their own, they would be called planets, unequivocally. In fact, a large number of the moons of Saturn and Jupiter are considerably larger than Mercury. They are planets that just happen to be orbiting bigger planets, and this is why an object's position or orbit should not be a consideration for the base classification.

 

 

If I were to use oDDity's "logic", I could arbitrarily say Mercury isn't a planet becasue it is too small and too close to the Sun, Jupiter isn't a planet becasue it is made of gas and is too big, Neptune isn't a planet becasue it hasn't "cleared its neighbourhood", Uranus isn't a planet becasue its axis of rotation is at a wildly different angle to the rest of the other planets, Venus isn't a planet becasue it is too hot and rotates the wrong way on its axis, etc. Now that would be pathetic, oDDity.

 

You need to get over your ice phobia.

 

You need a scientifically based classification that avoids arbitrary and sloppy definitions as much as possible, that can be applied to any object, anywhere.

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While I agree with you that the definition of "planet" shouldn't be based on orbit, I think you may have missed my point: If you don't have a problem with the definition of "satellite" taking into account orbit, how can you argue that there's something wrong with the definition of "planet" taking into account orbit? Although I don't care for this definition, I don't see anything "wrong" with defining a planet as a satellite in stable orbit around a star, with enough mass to be spherical due to gravity.

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While I agree with you that the definition of "planet" shouldn't be based on orbit, I think you may have missed my point: If you don't have a problem with the definition of "satellite" taking into account orbit, how can you argue that there's something wrong with the definition of "planet" taking into account orbit? Although I don't care for this definition, I don't see anything "wrong" with defining a planet as a satellite in stable orbit around a star, with enough mass to be spherical due to gravity.

 

 

The reason it is wrong is that it is fairly likely that there are numerous planets that have been ejected from their original orbit around a star, and are drifiting in interstellar space. It would be silly to call an object similar to Mars a planet when it is orbiting a star, and something else when it isn't. Planets are wanderers of the heavens - whether or not they are wandering near a star is not relevant to their base level object class.

 

Defining something as a satellite when it is orbiting somehting is appropriate, becasue the definition describes a behaviour that is particular to that circumstance. Earth is a satellite of the Sun, so calling something a planet and a satellite is fine as they are not mutually exclusive. Planet descibes what the object is satellite describes what it does.

 

So the reasons it would be wrong to use some kind of orbital information when describing a planet are:

 

*Redundant terminology - the word satellite already describes one object orbiting another.

*Needless exclusivity - the same object becomes different things depending on where it is if you use orbital information to define it. A planet is the same thing wether it is a billion light years form any other object or it is in a complex orbit around several other bodies, or something in between.

*Things need to be classifyable without reference to other things (as much as is possible), before you start layering other categories on them. You should be able to define a planet without referring to orbits, stars, neighbourhoods etc, and you should be able to do it in a way that does not involve the use of arbitrary units of distance etc. You can then layer information on top of the base category when and where it is relevent.

 

E.g Europa is a planet (as far as I am concerned), that is also a satellite of Jupiter which happens to be a satellite of Sol. Calling one type of object a planet becasue it primarily orbits the Sun and another a moon because it primarily orbits a planet is silly IMO. There are moons of Jupiter and Saturn which are clearly the same class of object as Mars or Mercury (or Pluto).

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oDDity - In looking at the new definition of planet... do you think the criteria they created are written clearly enough to rule out any and all uncertainty regarding which objects should and should not be classified as planets?

 

I'm curious what you think. You normally look at things in an absolute, logical and objective way. I'd be floored if you actually think these criteria are well-written and worthy to be in the next Webster's dictionary.

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Well on a technical level, Earth is one of the sun's moons, or at least you could argue that. So if we take this perspective, Europa could well be a planet, but it is still a moon of Jupiter etc.

 

Coming up with a fool-proof definition of a planet is not easy, as there is constant new data coming in which breaches that in some way.

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Well on a technical level, Earth is one of the sun's moons, or at least you could argue that. So if we take this perspective, Europa could well be a planet, but it is still a moon of Jupiter etc.

 

The word "moon" is just a redundant equivalent of the word "satellite". They really mean the same thing AFAIAC.

 

 

Coming up with a fool-proof definition of a planet is not easy, as there is constant new data coming in which breaches that in some way.

 

Which is all the more reason to avoid vague terms like "clearing the neighbourhood", and also why you should avoid definitions that make reference to other objects, or particular temperatures as much as possible. It needs to definable without using arbitrary units of measurment. And it needs to work regardless of where something is. It is difficult though, because there will always be things that are borderline between one class and another.

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Yeah true. I'd bet a million dollars that the definition will have to be rewritten a few more times in the future.

 

But yeah, "clearing it's neighbourhood" is pretty stupid, because imagine that a stray comet from the oort cloud pulverizes our moon, technically speaking Earth would'nt be a planet anymore - at least with this part of the definition.

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Yep. A planet's definition needs to be something like:

 

* Has a volume of at least 27,832,317mi^3 (~375mi in diameter) +/- 2,000,000mi^3.

* Is spherical or near-spherical in shape. (General elliptical shapes are acceptible as long as no one line drawn from any one point on the surface of the object through the center of the object to the same point on the opposite side of the object is less than 80% the length of any other line similarly drawn through the center of the object. Note: If an atmosphere is known to exist or if the celestial body is made entirely of gas, then the lines mentioned above shall instead be drawn to the known outermost portions of the atmosphere or gas body.)

* Rotates on a single axis. The angle of the axis does not matter and is allowed to change over time.

* Primary orbit is around a star or stars (e.g., binary star system) in a predictable or somewhat predictable manner (e.g., circular; elliptical).

* Orbit can pass through the path of another celestial object's orbit, including through the paths of other planets or moons.

* Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.

 

Note:

* Presence of an atmosphere or lack thereof is not a deciding factor.

* Presence of moons or lack thereof is not a deciding factor.

* Presence of rings or lack thereof is not a deciding factor.

* Material composition of the body is not a deciding factor.

* Existing or non-existence of magnetic poles is not a deciding factor.

* Presence of life or lack thereof is not a deciding factor.

 

Just my $.02. This is just an example! But I feel a definition similar to what I made above goes a long way toward making the definition a lot less nebulous than it is. I doubt the above would be totally bullet-proof either, but I'm not an astronomer. I would think astronomers could've done a lot better than they did. (FYI, the 'sufficient mass' one is not my own. It was taken from the IAU site.)

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Yep. A planet's definition needs to be something like:

 

* Has a volume of at least 27,832,317mi^3 (~375mi in diameter) +/- 2,000,000mi^3.

* Is spherical or near-spherical in shape. (General elliptical shapes are acceptible as long as no one line drawn from any one point on the surface of the object through the center of the object to the same point on the opposite side of the object is less than 80% the length of any other line similarly drawn through the center of the object. Note: If an atmosphere is known to exist or if the celestial body is made entirely of gas, then the lines mentioned above shall instead be drawn to the known outermost portions of the atmosphere or gas body.)

* Rotates on a single axis. The angle of the axis does not matter and is allowed to change over time.

* Primary orbit is around a star or stars (e.g., binary star system) in a predictable or somewhat predictable manner (e.g., circular; elliptical).

* Orbit can pass through the path of another celestial object's orbit, including through the paths of other planets or moons.

* Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.

 

Note:

* Presence of an atmosphere or lack thereof is not a deciding factor.

* Presence of moons or lack thereof is not a deciding factor.

* Presence of rings or lack thereof is not a deciding factor.

* Material composition of the body is not a deciding factor.

* Existing or non-existence of magnetic poles is not a deciding factor.

* Presence of life or lack thereof is not a deciding factor.

 

Just my $.02. This is just an example! But I feel a definition similar to what I made above goes a long way toward making the definition a lot less nebulous than it is. I doubt the above would be totally bullet-proof either, but I'm not an astronomer. I would think astronomers could've done a lot better than they did. (FYI, the 'sufficient mass' one is not my own. It was taken from the IAU site.)

 

Your definition is way, way too complicated, and has several problems with it.

 

First, using absolute units, such as suggesting that the object have a volume of 27,832,317mi^3, is totally out of the question. Such a measure is arbitrary in the extreme, and relies on too meany other things being defined. You need to be able to frame it in the context of a unit independent measure, such as the ratio of the polar to equatorial diameter, corrected for distiortions caused by orbiting masses and axial rotation.

 

Second, rotation is irrelevent. your definition would exclude Uranus, whuch has a somewhat complex rotation, and it doesn't account for objects that barely rotate at all. I don't know why you even thought that was worth mentioning, it seems like a pretty bizarre criterion, frankly.

 

Third, it doesn't take into account objects ejected from the orbit of a star, and are located in interstellar space.

 

 

A simple definition is all that is required:

 

Object is large enough to form a spheroid (as measured by the above test - a polar to equatorial ratio corrected for distortion of approximately 1:1) by self gravity is all you need. If you want to make a distinction between stars and planets, you can add the clause that it is not so large that it spontaneously initiates a fusion reaction. Of course, you will have to arrive at a somehat arbitrary decision as to how much of a deviation from spheroidal is acceptable, but that is kind of moot when you have corrected for things that will distort a planet's shape.

 

If your definition is more complex than that, you are barking up the wrong tree.

 

There are billions upon billions of planets in the universe, I don't know why people want to keep coming up with contrived reasons to limit the number to 8 or less.

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I'm pretty sure the tendancy to form a sphere shape depends heavily on the materials making up the object. It's not just self gravity that nudges things in the direction of sticking together and minimizing surface area for a given volume with a sphere shape. There are also contact forces, hydrogen bonding, interface energies between different materials, etc.

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Obscurus, grow up and stop whining. You've lost. Pluto isn't a planet any more, and that's that. IF they do reverse the decision, then you can start crying again, but until then, Pluto officially isn't a planet, no matter what your views are.

You may as well start a petition to get blue reclassified as red, becasue you personally are unsatisfied with it.

I don't have to argue my case, my longstanding view that pluto isn't a plaent has been unheld.

Christ, you're the guy who keeps bleating on about how it's all semantics anyway and doesn't matter, yet 90% of the fervent rantings in this thread belong to you.

Every time I read one of your posts, I get the image of Hitler standing at that lectern in Nuremberg, waving is arms about and trying to convince everyone that Jewish heads are the wrong shape.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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Obscurus - I was not submitting my definition as one that should be scrutinized and possibly used by the IAU as the definition they should adopt. Like I said, it was simply an example and I'm not an astronomer. Using precise things "such as" volume, or diameter, or mass, or its orbitate or rotation qualities, or its shape or composition, etc. should at least be considered to help define what a planet is or should be. I don't know what criteria should be used, but having definites like that is what I feel are needed. I was only giving examples.

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@Obscurus: My point is that you're arbitrarily assuming that having "planet" describe the size/shape of something is superior to describing its behavior. There's nothing inherently wrong with choosing a definition of "planet" such that Earth would no longer be a planet if it were ejected from the solar system, just as there's nothing inherently wrong with choosing a definition of "moon" such that Luna would no longer be a moon if it didn't orbit a planet. You seem to have your own predefined view about what it means or doesn't mean to be a planet, and you're religiously arguing that it's better than other, entirely different definitions. It seems no different than people who like to argue Europa can't be a planet because in their predefined view, one planet cannot orbit another.

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I think a planet should be something that is

 

1) spherical in shape

2) orbiting a star, and

3) interesting enough to the general population that it has featured in at least one science-fiction film or TV show

 

After all, there is no point in having a planet nobody has heard of, it might as well just be an anonymous bit of rock.

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Careful or your definition will cover Tom Arnold.

 

 

 

(at least circa 1990s; pudgy, Rosanne, "The Tom Show")

Edited by demagogue

What do you see when you turn out the light? I can't tell you but I know that it's mine.

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Obscurus, grow up and stop whining. You've lost. Pluto isn't a planet any more, and that's that. IF they do reverse the decision, then you can start crying again, but until then, Pluto officially isn't a planet, no matter what your views are.

 

 

I am not whining because Pluto was reclassified, I am whining because of the dubious grounds on which it was reclassified. If the IAU comes up with a scientifically defensible defintion of a Planet that excludes Pluto or any other object from planetary status, that is fine. But at the moment, I and a very large number of other scientists, regard the currrent definition as unscientific bunk. It isn't the semantics that bothers me, it is the lack of scientific rigour and lack of consistency and clarity that causes me such consternation. At the moment, there are potentially a number of objects that are bigger than Mercury that would now classified as "Dwarf Planets", yet somehow Mercury retains its status as a planet. There are now a huge number of extrasolar planets that are no longer planets becasue of sloppy wording by the IAU. Most of the planets in the Solar System do not pass the criterion of "clearing their neighbourhood", and vague as it is, there is no way you can say Pluto isn't a planet without also demoting Neptune. And arguably any planet with moons has failed to clear it's neighbourhood, and thus isn't a planet. Sloppy wording and inconsistent reasoning are where my issues lie, not with semantics as such.

 

Redefine your terminology if you will, but at least be consistent and clear.

 

And you are the one who needs to grow up if you think that by expressing a perfectly valid opinion I am somehow comparable to Hitler. I find that rather offensive, frankly. Instead of arguing your case coherently (which you normally at least attempt to do), you simply back out without even trying to counter my arguments, (which incidentally, are shared by a very large number of my fellow scientists, so it is not as though I am alone in my opinions) and launch dubious ad hominem insults at me. Real mature, oDD.

 

@Dram: "Uranus DOES rotate around a single axis, though it is a wierd one. Or are you referring to that it also orbits the sun and thus means it has 2 axes?"

 

Well, like all planets, Uranus has precessional motion, meaning it's axis of rotation moves around a bit, however, Uranus' axis of rotation was highly altered by a passing planet sized object at some point, and it is still not really stable. Since a planet's axis of rotation can potentially be easily changed by a passing mass, it is a very poor criterion on which to define something.

 

@Ishtvan: "I'm pretty sure the tendancy to form a sphere shape depends heavily on the materials making up the object. It's not just self gravity that nudges things in the direction of sticking together and minimizing surface area for a given volume with a sphere shape. There are also contact forces, hydrogen bonding, interface energies between different materials, etc."

 

Material density is really the only major factor in determining the size at which self gravity will collapse an object into a spherical shape. A low density cloud of gas will need to be much bigger than a lump of rock to collapse into a spherical shape under it's own weight. The material on object is made of will of course affect this behaviour, but if you are going to use material as a criterion, then you need to create a new set of classifications.

 

Gaseous objects will need a different name to rocky objects, which will need a different name to liquid objects etc. You can't just say everything that is made mostly of water in a solid state isn't a planet, everything else is - there is no consistency there at all.

 

 

@Gildoran: "My point is that you're arbitrarily assuming that having "planet" describe the size/shape of something is superior to describing its behavior. There's nothing inherently wrong with choosing a definition of "planet" such that Earth would no longer be a planet if it were ejected from the solar system..."

 

Good point. See oDDity, these are the sort of arguments you could have used, as an alternative to childish personal attacks.

 

However, to be scientifically useful, a classification scheme that defines the fundametal class of an object needs to be able to do so in the context of the object in isiolation, without reference to other objects where possible.

I suppose you could have a scheme where the base category is simply "object", and "planet" is an object with certain properties, such as above a certain size, orbiting a star etc. I wouldn't have a problem with that per se, except that it creates issues of clarity of its own, and measn that if you come across an Earth-like object deep in interstellar space, you need to invent yet another term to describe it.

 

My preferred option is to minimise the number of definitions and classes by using a hierarchical system, rather than coming up with a special name for every possible object in every possible situation.

Edited by obscurus
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