Pluto Might Be Bigger Than Eris

astroengine writes "Look out, the battle of the dwarf planets is about to re-ignite! During last weekend's rare occultation of a star by Eris, astronomers managed to gain one of the most accurate measurements of Eris' physical size. When three Chilean telescopes watched the star blink out of sight, astronomers were shocked to find that Eris is actually a lot smaller than originally thought. So small that it might be smaller than Pluto. On speaking with Discovery News, Eris' discoverer Mike Brown said, 'While everyone is more interested in the "mine is bigger than yours" aspect, the real science is the shockingly large density of Eris.' The mass of Eris is well known, so this means the object is more dense than Pluto. Does this mean the two mini-worlds have different compositions? Did they evolve differently? In light of this finding, is the underlying argument for Pluto being demoted from the planetary club on wobbly ground?"

Comments

Hey you guys

[Anonymous Coward]

Mine is bigger than yours! Ha!

Re:Hey you guys

[Jeremiah Cornelius]

Bigger than 'Er arse? My arse? Yer arse?

'Er arse ain't 'alf bad, as 'tis!

Re:Hey you guys

[KDR_11k]

HEY FATASS! Move it, you're crushing my plums!

Requisite

[Enderandrew]

http://xkcd.com/473/

Re:Requisite

[EvilBudMan]

Bluto Blutarski was bigger than that.

Re:Requisite

[danlip]

also: not a planet, neener neener http://xkcd.com/482/

Re:Requisite

[Anonymous Coward]

best xkcd ever!

Re:Requisite

[Anonymous Coward]

Wow... did you see what this brave Coward did here? You see, someone took an XKCD comic, and then brilliantly lampooned it by postpending an image of the goatse guy, and changing the title of the strip both as a whole and as the daily offering to one that reflects the fact that they added a picture of a man stretching out his anus. Now, I admit, it probably wasn't OUR coward that made this delightful parody, but our Coward had the creative wherewithal and daring to conceive of the act of making a link to aforementioned page, after someone else made reference to an XKCD strip. Bravo, young Coward. Bravo. Everyone here in the third grade solemnly approves of your wit and gallantry. In fact, we are asking around to see if anyone has an older sister so that we may be able to arrange for you, stalwart and stouthearted Coward, to touch a boobie.

Cue

[Haedrian]

[Insert Ur-anus size joke here]

Re:Cue

[EyelessFade]

Professor: "I'm sorry, Fry, but astronomers renamed Uranus in 2620 to end that stupid joke once and for all."
Fry: "Oh. What's it called now?"
Professor: "Urectum. Here, let me locate it for you."

No.

[bigspring]

The argument for calling Pluto a Dwarf planet is on perfectly firm ground. It had nothing to do with size. Do some research before you ask stupid questions, please.

Re:No.

[Sique]

The argument was as arbitrary as any others. It was basicly "which property is common to both Pluto and Eris, but not found in the other objects traditionally considered planets?".

Pluto always was a weird object to be called a planet, with his density somewhere in the nowhere between the earthlike planets and the gas giants, and being pretty similar to the large moons of the gas giants.

But only when Eris was found, there was a second objekt thought to be similar enough to Pluto to define a new class of "plutolike objects", which allowed Pluto to be demoted from planet status.

So yes, the classification of Pluto in the class of "plutolike objects" (pardon, "Dwarf planets") seems to be on pretty firm ground, considering there are now more objects known in that class (Makemake for instance), though Eris now seems to be a weirdo within this class.

Re:No.

[lgw]

It's perfectly simple: Pluto is not a Dwarf Planet, Pluto is a Fucking Planet. Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

Re:No.

[bigspring]

I wasn't arguing how arbitrary it was. I was arguing that the people who created the definition were smart enough to define it in such a way that the classification can be determined on a case-by-case basis. A basis that won't be substantively changed by comparative measurements. Discovering anything about any new planetary body will not change Pluto's classification because the discoveries will not be about Pluto.

Re:No.

[MozeeToby]

It's perfectly simple: Humans are not animals, Humans are fucking special. Ask just about anyone religious and my age, they'll tell you so: "No, humans aren't animals, now stop trying to change things".

See how ridiculous your non-argument sounds?

Re:No.

[geekoid]

Fuck you... allow me to elaborate.

Science progress, and you geezers* can stuff yourselves. For the record, I'm probably older then you. You can gave geeky, I'll stick with nerdy, because I actually know shit.

I'm sure there where people like you when the Greeks figured out the world was round, and there were people like you when the write brothers flew, and there where people like you when phones went cordless, and there will be people like you when we send people to actually walk on Pluto.

We don't need you're attitude, we will never need your attitude. You are an achor around the ankle of progress. But we are stronger then you, and science will continue no matter how much you want it to freeze in place.

*By Geezer I mean: unchanging, 'in my day', 'get off my lawn' wastes of space.

Re:No.

[Anonymous Coward]

Fuck you... allow me to elaborate.

Science progresses, and you geezers* can stuff yourselves. For the record, I'm probably older than you. You can have geeky, I'll stick with nerdy, because I actually know jack shit.

I'm sure there were people like you when the Greeks figured out the world was round, and there were people like you when the Wright brothers flew, and there were people like you when phones went cordless, and there will be people like you when we send people to actually walk on Pluto.

We don't need yyour attitude, we will never need your attitude. You are an anchor around the ankle of progress. But we are stronger then you, and science will continue no matter how much you want it to freeze in place.

*By Geezer I mean: unchanging, 'in my day', 'get off my lawn' wastes of space.

You almost made a decent argument, although it was mostly emotional and not rational. Too bad you write like a fucking 3rd grader.

Re:No.

[by (1706743)]

At the end of the day, the whole "planet/not a planet" distinction isn't even particularly illuminating. It's much more useful, IMHO, to just look at the parameters and make up your own mind. How massive is it? What's its distance from the sun? What's its eccentricity? What's its inclination (please, no jokes about Uranus' inclination...)? What's its origin?

A binary planet/not planet distinction just doesn't tell you that much.

Re:No.

[Anonymous Coward]

Pot, kettle. Kettle, pot.

Re:No.

[Anonymous Coward]

Eris a weirdo? No fnord way!

Re:No.

[Anonymous Coward]

Do I qualify? I remember watching the moon landing, and got my first personal computer in 78. Sorry, but Pluto /was/ a planet, and those kids aren't on /your/ lawn.

Re:No.

[icebraining]

Fuck you... allow me to elaborate.

Science progresses, and you geezers* can stuff yourselves. For the record, I'm probably older than you. You can have geeky, I'll stick with nerdy, because I actually know jack shit.

I'm sure there were people like you when the Greeks figured out the world was round, and there were people like you when the Wright brothers flew, and there were people like you when phones went cordless, and there will be people like you when we send people to actually walk on Pluto.

We don't need your attitude, we will never need your attitude. You are an anchor around the ankle of progress. But we are stronger than you, and science will continue no matter how much you want it to freeze in place.

*By Geezer I mean: unchanging, 'in my day', 'get off my lawn' wastes of space.

You almost made a decent argument, although it was mostly emotional and not rational. Too bad you write like a fucking third grader.

Re:No.

[smellsofbikes]

>Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

And ask anyone my grandmother's age and they'll tell you that they're not really convinced Pluto is a planet because when they were in school in the 1920's, it wasn't a planet, it was just a chunk of rock that nobody had ever seen.

Re:No.

[khallow]

I wasn't arguing how arbitrary it was. I was arguing that the people who created the definition were smart enough to define it in such a way that the classification can be determined on a case-by-case basis. A basis that won't be substantively changed by comparative measurements. Discovering anything about any new planetary body will not change Pluto's classification because the discoveries will not be about Pluto.

Here's the definition: "The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune." The rest of the definition is noise because they failed to define "clearing the neighborhood".

Re:No.

[Jodka]

from the article summary:

"Look out, the battle of the dwarf planets is about to re-ignite! During last weekend's rare occultation of a star by Eris.

from the parent post:

Fuck you... allow me to elaborate.

from wikipedia

Eris is named after the Greek goddess Eris (Greek ), a personification of strife and discord.

Re:No.

[Chris Burke]

The rest of the definition is noise because they failed to define "clearing the neighborhood".

Noise?!

There's FIVE ORDERS OF MAGNITUDE difference in planetary discriminant (mass ratio between the body and all other masses in that orbit) between the highest value for a dwarf planet (Ceres) and the lowest value for a planet (Neptune).

When the difference is a factor of 10,000, there's absolutely no need to create a precise definition, and it would be foolish to do so.

It's like you're arguing that the definition of what is or isn't ocean is useless because it doesn't precisely define at what point of the tide cycle, or how far up a river mouth, it transitions from ocean to not ocean. But the question we're asking is whether Topeka, Kansas is in the ocean or not and the answer is obviously NO!

You might as well argue that it's completely arbitrary to say that you are alive and Benjamin Franklin is dead, because science has not precisely defined the exact line between dead and not dead. Um, I think it's still pretty clear which is which in this case.

You see, if they did actually define "clearing the neighborhood" in a precise manner, that would be the truly arbitrary choice. But when you look at the bodies in our solar system, and you see that there's a small set of objects which outweigh everything else in their orbits by at least a thousand-to-1, and then a great many objects which weigh less than the rest of the objects in their orbit, then yes that actually makes a clear dividing line. You don't have to draw it with infinite precision to see that it's there.

The definiton of Pluto as a planet is far more "noise" than the definition that it isn't. We only called it a planet because we didn't know it was so different from the other ones. It's like when we first discovered Ceres. Only we changed that one pretty quick, even though it's more planet-like than Pluto is.

Re:No.

[digitig]

"Hail Pluto!"

Doesn't work, does it?

Re:No.

[Chris Burke]

It's perfectly simple: Pluto is not a Dwarf Planet, Pluto is a Fucking Planet. Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

And you'll be as wrong as those who resisted reclassifying Ceres from planet to non-planet.

Oh, what's that, you don't think Ceres is a planet? It's pretty obvious that what just happens to be the biggest asteroid in a giant asteroid belt that's total mass is 3 times this one body is cool, but not a planet?

Yeah, that's exactly what geeks will be saying about Pluto in twenty years.

Tradition, not any salient facts, are the only reason people resist reclassifying Pluto. Tough. Science moves on. We know things about (Ceres|Pluto) that we didn't know when we discovered it. You can adjust to this knew information, or you can stamp your foot and refuse to change.

Which is fine. But the world will change with or without you.

Re:No.

[Anonymous Coward]

Fuck you... allow me to elaborate...

Your mouth is like Uranus.

Re:No.

[Anonymous Coward]

Fuck you... allow me to elaborate.

Not necessary. I think your first sentence was a perfect and complete response to most slashdot articles and comments.
Please STFU while you are still ahead.

Re:No.

[khallow]

There's FIVE ORDERS OF MAGNITUDE difference in planetary discriminant [wikipedia.org] (mass ratio between the body and all other masses in that orbit) between the highest value for a dwarf planet (Ceres) and the lowest value for a planet (Neptune).

You do realize that nothing significant comes within 11 AU of Pluto aside from Charon and possibly an occasional rare visit from Eris? That's more than a third of the distance to the Sun.

Re:No.

[Anonymous Coward]

Ask just about anyone geeky and my age...

Yeah, all scientists should just do that. Stop fucking publishing stupid tedious peer-review shit. Ask Slashdot instead. Anyone on Slashdot knows everything about any and every important question in science, besides having a 10 inch dick and an IQ of 180.

Re:No.

[Merls the Sneaky]

Here's the definition: "The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune." The rest of the definition is noise because they failed to define "clearing the neighborhood".

The problem I have is that Pluto crosses the orbit of Neptune, therefore making Neptune a non planet by the same definition.

Re:No.

[dimeglio]

What about plutonium? The element was named after a planet. If Pluto is no longer a planet what then, rockonium?

(Jim doesn't know about Pluto and plutonium. The element is now called rockonium. Travelling back in time, they are looking for fuel.)

"Sir, we'll need rockonium to power these old engines."
"Scotty, we cannot use rockonium, this thing called plutonium is all we have."
"But sir... it will take weeks to adapt these engines. Even if I'm able to do it, we might all blow-up."
"Scotty, you have 4 hours."
"...but..."
"Here's the plutonium."
2 Hours later
"Jim, the engines are ready."

Re:No.

[jthill]

See the guy who did it talk about how it happened.

He rebuilt the Hayden Planetarium's exhibit to account for the new stuff being discovered. They wanted to present generally what's out there, so they grouped like with like: the inner planets, the gas giants and the Kuiper belt. Pluto plainly is not a gas giant at all and looks a lot like what's in the Kuiper belt, so wtd?

Apparently, when you're looking at how much crap really is in orbit around our sun , there isn't much question what to do, but it seems like a much bigger deal to people who haven't yet looked. .

Re:No.

[uvajed_ekil]

It's like you're arguing that the definition of what is or isn't ocean is useless because it doesn't precisely define at what point of the tide cycle, or how far up a river mouth, it transitions from ocean to not ocean. But the question we're asking is whether Topeka, Kansas is in the ocean or not and the answer is obviously NO!

But the land that is now Topeka, Kansas was at times covered by ocean waters, including at least during the early Cretaceous. So maybe Eris once cleared its neighborhood, before a lot of "less desirables" moved in and it went down hill? Or perhaps it was a small neighborhood that was cleared, then bought-up via eminent domain then redeveloped? Or maybe the rules are different with such long orbits?

You might as well argue that it's completely arbitrary to say that you are alive and Benjamin Franklin is dead, because science has not precisely defined the exact line between dead and not dead. Um, I think it's still pretty clear which is which in this case.

But science has not definitively proven that time only flows in one direction, so the past and future are equivalent, which must make the instant of the present irrelevant. Then maybe Ben Frnaklin is as alive as us, and we are as dead as him.

Just kidding, I felt like being an argumentative moron. Too bad the minor planet advocates don't understand the statistical significance of orders of magnitude.

Re:No.

[KDR_11k]

Was it really named after the planet or was it named after the Roman god of the underworld?

Re:No.

[Cochonou]

I really fail to see how Pluto is so much more different from Earth than Earth is from Jupiter. This planetary discriminant as a way to measure the cleanliness of an orbit is an interesting metric, but it is a bit strange to define an object according to its surroundings. A much more relevant metric to characterize an object would be its mass. There are two to three orders of magnitude of difference between the mass of Pluto and Earth, and there is about the same order of magnitude difference between Earth and Jupiter. Likewise, the composition of Earth and Jupiter are totally different, but that does not preclude them from both being called planets.

Re:No.

[Anonymous Coward]

A "Fucking planet" - that's a new category, what evidence do you have to support this new category.
Where is the genatalia located (Uranus perhaps)

Do we have any video? we will need to speed it up, I believe planets are rather large which typically means slow
Is there reproduction involved or are planets sterile?

You also imply that others share your categorisation of Pluto as a Fucking Planet, please elaborate. Is there an offical lobby group or is it just a few (one?) people you know?
You imply technical ability and age are important in the acceptance of the Fucking Planet category.
I am pushing 50 and Pluto has always been the odd planet out, Small, highly elliptical orbit and and different orbital plane. I (along with many others) have no problems with it being recateg

Re:No.

[Anonymous Coward]

Absolute distances are pointless when we're talking about orbits. I can't be arsed to make the exact calculation, but wouldn't 11 AU be around a fifth of Pluto's orbit?

Re:No.

[OolimPhon]

You do realize that nothing significant comes within 11 AU of Pluto aside from Charon and possibly an occasional rare visit from Eris? That's more than a third of the distance to the Sun.

Er, apart from the fact that Pluto's orbit crosses that of Neptune?

It seems to me that once in a while those two ought to come fairly close, no?

Re:No.

[khallow]

Er, apart from the fact that Pluto's orbit crosses that of Neptune?

If I recall correctly, the distance of closest approach is somewhere around 17 AU (that is, how close Pluto actually gets to Neptune). Uranus gets closer than Neptune does. That's because Neptune and Pluto are in resonance.

Re:No.

[khallow]

Pluto has an eccentric orbit, it's between 29 and 49 AU. I was referring to closest approach. BTW, if the mass estimates for the Kuiper belt objects are correct, there's something like 5-50 times Pluto's mass in total in the area where Pluto orbits. It is likely then that at any given time, a relatively large amount of mass is within a third of Pluto's current distance to the Sun even if no major planets ever are.

Re:No.

[khallow]

I withdraw my original complaint. It turns out that there's estimated to be somewhere around 5-50 Pluto masses of material in the Kuiper Belt objects between roughly 30 and 55 AU.

Kuiper belt masses were initially estimated on the assumption that all KBOs have albedos of 0.04, like the nuclei of the Jupiter-family comets. These initial estimates gave masses 0.1 M [that is, 0.1 Earth masses - khallow] (Jewitt et al., 1998). Recent measurements of large KBOs suggest albedos on average about three times larger but it is not known if this is generally true or if the high albedos apply only to the largest KBOs (we cannot yet measure the smaller ones directly). In any case, 0.1 M is an upper limit to the total mass. With mass scaling as (albedo)^(3/2), the derived mass is 3^(3/2) 5 times smaller than first thought, corresponding to a few percent of an Earth mass. These estimates are still quite uncertain because we possess few reliable determinations of the albedos, because we do not know the densities of most KBOs and, especially, because we have meaningfully sampled only the inner regions of the Kuiper belt. For all these reasons, the relative masses of the various components of the Kuiper Belt are uncertain. A reasonably safe conclusion, however, is that the mass of the scattered disk objects is larger than the mass of the other components of the Kuiper belt (Trujillo et al., 2000).

[I had to manual edit the exponentials because superscripts aren't supported by Slashdot. So there's up to 50 times as much mass (Wikipedia is claiming 5-50 Pluto masses worth, using current estimates for Pluto's mass). Anyway, with that much mass swimming around, it's very likely that Pluto has at least a Pluto's worth in mass of other Kuiper belt objects within the neighborhood I specified. Which would mean it is not a planet even under a different definition of neighborhood.

Re:No.

[Anonymous Coward]

The Matter in question requires very little Deliberation: the Celestial Space is not a Vacuum, instead, it is filled with Luminiferous Aether. I urge you, Sir, to enquire any Person who has an overriding Interest in Matters concerning the Sciences and their Application and whose Age is similar to mine, and they shall - with Derision - exclaim: "Why, Sir, the Celestial Space is filled with Luminiferous Aether! Cease your attempts to alter things forthwith!".

Re:No.

[pommiekiwifruit]

Those elements form a series, each further away from the earth: Uranus, Neptune, Pluto, America.

Re:No.

[jc42]

Here's the definition: "The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune." The rest of the definition is noise because they failed to define "clearing the neighborhood".

Actually the original list when the term "planet" was coined was "Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn". At the time, Uranus was apparently unknown to European scientists, though it was known to people with good eyes in other parts of the world with clearer skies. Neptune wasn't known until 1846.

The current list of eight planets is the result of several revisions that had less to do with science than with the media. At one point, the revision was basically to exclude Ceres, which fit the previous definition, and hardly anyone wanted that. We can expect further revisions in the future, and they'll be as inconsequential as the earlier revisions. This won't stop people from discussing the topic endlessly.

Re:No.

[rizole]

Hummmmm... noodles.

Re:No.

[lgw]

Tradition, not any salient facts, are the only reason people resist reclassifying Pluto. Tough. Science moves on.

The term "planet" has no scientific use. It does have a traditional one, and by tradition, Pluto is a Fucking Planet. Add Eris too if you like, but you can't take Pluto from me!

Sounds about right

[Pojut]

This sounds about right; the Eris is a fairly tiny phone.

Oh wait...

Pluto controversy

[falldeaf]

I remember being so confused about the Pluto controversy. Maybe it's just because I'm not an astronomy nerd but I don't understand the uproar about correcting a miss-classification of a heavenly body... I remember Neil Desgrasse Tyson on the Colbert Report chiming in that it was just a simple fact. Any of you astronomy nerds reading that could explain the emotional reaction? (Not to assume, was it astronomy nerds that were upset? Maybe it was Astrology people that were upset.)

Re:Pluto controversy

[just_another_sean]

I also seem to remember Neil blaming most of the uproar on Disney. Paraphrasing - "if they hadn't named that darned dog Pluto nobody would have cared".

It's hard to tell with Neil how serious he was on that one. :-)

Re:Pluto controversy

[Anonymous Coward]

I figured it was the parents who were upset that their children were learning something different from what they learned.

Re:Pluto controversy

[fuzzyfuzzyfungus]

I think that it has a lot to do with the fact that a shockingly large number of people confuse nomenclature with knowledge. Because of that, a fairly fiddly technical discussion over how best to handle astronomical nomenclature hit the popular press as "zOMG pointy-headed scientists don't even know if Pluto is a planet!!!!!"

Naming is not a trivial thing, good nomenclature makes the world a much easier place, crap nomenclature makes it a mess wholly without reason; but either way it seduces people into forgetting that names are simply constructs, assigned for our convenience to bundles of real things. Sometimes, you have to revise the constructs to make the nomenclature better, simpler, more expressive, whatever; but that is very different from changing the bundle of real things and attributes.

Re:Pluto controversy

[falldeaf]

Hey that's a pretty good guess.

Re:Pluto controversy

[sznupi]

At least we can be certain it will pass - I don't see any people lamenting that Ceres, Pallas, Juno and Vesta have lost their planetary status.

Status which they had, for half a century after their discovery. Similar to Pluto.

(for that matter, the same applies to the Sun - it was also classified as a planet at some point)

Re:Pluto controversy

[Anonymous Coward]

(Maybe it was Astrology people that were upset.)

Nope just Sailor Moon fans.

Re:Pluto controversy

[geekoid]

It's because there wasn't a real clear definition of 'planet' and years of science education turned out to be wrong*. People, in general, aren't taught to understand that things change and new data can change scientific understand and labels.

You can see this type of emotional attachment as people talk about changes classifications on animals to reflect the science.

Plus the media told people like it was some shocking and wildly controversial opinion; which it is not. It's a fact.

*well, not wrong per se, just not clearly defined.

Re:Pluto controversy

[Hatta]

The problem is that nobody was taught a planetary mnemonic that included Ceres, Pallas, Juno, and Vesta. As far as people are concerned if it's in the mnemonic, it's a planet. If it's not, then it's not. Their understanding doesn't go any further than that. To them, saying "pluto isn't a planet anymore" is very much like saying "Q isn't a letter anymore".

Re:Pluto controversy

[John Hasler]

> It's a fact.

No it isn't. It's a definition, and an arbitrary one since the class "planet" as currently defined has no particular physical significance. "Member of the list of planets of Sol" is no less (and no more) "factual".

Re:Pluto controversy

[Jiro]

It's not a misclassification. It's not as if they had a definition of a planet and then suddenly figured out that Pluto didn't fit it--that would be a misclassification. Pluto is no longer classified as a planet because they wrote the definition just now specifically to exclude it.

Re:Pluto controversy

[rarel]

Q- "I'm not a letter, I'm a free, uh... alien of nearly infinite power!"

Star Trek: The Next Generation - The Lost Episodes

Re:Pluto controversy

[Estanislao Mart�nez]

I think that it has a lot to do with the fact that a shockingly large number of people confuse nomenclature with knowledge.

Yes, but who is confusing nomenclature with knowledge here? I think the scientists who pushed for this redefinition are as culpable of that as anybody. We can state all of our knowledge of a celestial object without settling the "question" of whether it's a "planet" or not. Our theories of physics spell out what are the sorts of actual physical facts that we can enumerate about celestial objects (mass, trajectory, composition, chemical and nuclear reactions, etc.). "Is it a planet" is not one of those. Because of this, drawing up some gerrymandered definition does nothing for our knowledge.

We're not the ancient Greeks. They had a distinct concept of "planet" because they saw some "stars" (in the old sense of the term, which means "celestial object") that, compared to others, moved funny. Because of this, they formulated laws of planetary motion distinct from laws of the motion of other "stars." We don't have those because, um, we unified the various theories of celestial and terrestrial motion a few hundred years ago.

In recent decades, we've been finding celestial objects that have all sorts of combinations of composition and trajectory. This is exactly what we should expect from our physical and cosmological theories. The general case is that space has all sorts of stuff floating around in all sorts of trajectories. With better telescopes, since we can see more stuff, we're seeing a lot more random stuff that's unlike what we'd seen before in all sorts of small ways.

Re:Pluto controversy

[Anonymous Coward]

The problem is that nobody was taught a planetary mnemonic that included Ceres, Pallas, Juno, and Vesta.

Hoho! Are you really sure about that? There's quite a bit about 19th-century culture that is NOT common knowledge anymore, so don't be so quick to assume that just because you never heard of it, it didn't exist.

Re:Pluto controversy

[Anonymous Coward]

I remember being so confused about the Pluto controversy. Maybe it's just because I'm not an astronomy nerd but I don't understand the uproar about correcting a miss-classification of a heavenly body...

You try not to get excited about heavenly bodies.

Re:Pluto controversy

[TimSSG]

Are Dwarf people no longer considered people?
Are Dwarf horses no longer considered houses?
FYI: Dwarf planets IS NOT the Official name last time I checked; it is a place holder till the think up a better English name.
Tim S.

Re:Pluto controversy

[Anonymous Coward]

Of course naming is a trvial thing. It's the most trvial of all.

What something is named does not in the slightest change what the something actually IS.

The object we call Pluto is whatever it IS. Whether we call that a planet or a cupcake or a stubbed toe makes no difference whatsoever. The object we call Pluto is what it is.

A chunk of metal commonly called iron is exactly the same whether we call it iron or jello or something unpronouncable in English. Every single atom of that iron exists all the same completely without regard to what name is attached to it.

Human beings are completely obsessed with naming every single thing from sub atomic particles all the way to planets and stars and galaxies. But not a single one of those names has had or will ever have any real impact on any of those named things.

Names will never change any of them. Never.

Try this: attach a name to a body that may or may not be a planet. The body will continue to follow its orbit quite unaware that you exist or that you have attached a name, argued with anyone else about the validity of that name, and long after you are dead and gone and have turned into dust, the object that may or may not be a planet will continue to follow its orbit quite unaware that you ever existed.

Names, I argue, are therefore completely trivial and meaningless. They serve only as a matter of human convenience. But have no other relationship with the universe. As humans are irrelevant to the universe, so are their names.

Re:Pluto controversy

[riverat1]

That's one of the reasons some people don't like science. When new information is found it changes. Many people have authoritarian/absolutist personalities and they don't deal well with change.

Re:Pluto controversy

[Chris Burke]

No it isn't. It's a definition, and an arbitrary one since the class "planet" as currently defined has no particular physical significance.

You don't find it significant that there are 8 bodies in the solar system that have a larger than 1000:1 ratio of their mass to the mass of other objects in the orbit, and that the object with the next largest ratio after that is well under 1:1? I think it indicates a very significant orbit-clearing ability for the larger bodies that Pluto, Ceres, and Eris simply don't have.

Even if you don't think it is significant, it certainly is a fact.

I guess technically "I think Pluto should still be a planet for entirely sentimental reasons" is still a factual statement. But it's a fact about the person saying it, not about Pluto.

Re:Pluto controversy

[Tim the Gecko]

Are Dwarf horses no longer considered houses?

I know this one!
They are not considered houses. Mostly.

Re:Pluto controversy

[Anonymous Coward]

The problem is that nobody was taught a planetary mnemonic that included Ceres, Pallas, Juno, and Vesta. As far as people are concerned if it's in the mnemonic, it's a planet. If it's not, then it's not. Their understanding doesn't go any further than that. To them, saying "pluto isn't a planet anymore" is very much like saying "Q isn't a letter anymore".

Who the hell really needed a stupid mnemonic to remember the names of the planets? Apparently people too stupid to really be able to care about the argument.

Re:Pluto controversy

[ultranova]

Nope just Sailor Moon fans.

But then again, there seems to be a general fanon consensus that Pluto is a homi/genocidal psychopath, so this could be seen as a karmic punishment. Or perhaps this is the very reason she went over the edge: "Demote my planet, will they? I'll show them! I'll show them ALL! MUAHAAHAHAHAAA!!!

...What?

Re:Pluto controversy

[ultranova]

No it isn't. It's a definition, and an arbitrary one since the class "planet" as currently defined has no particular physical significance. "Member of the list of planets of Sol" is no less (and no more) "factual".

The word "continent" is also a matter of definition: how large does an island have to be before it qualifies? However, for practical purposes, there is a sharp divide between major and minor land masses, just as there is a sharp divide between major and minor solar satellites.

Of course, we could simply agree that "planet" means one of the nine, and use "major satellite" and "minor satellite" in a scientific context.

Re:Pluto controversy

[m50d]

I still care about Ceres and Vesta. Not the other two, if it's not big enough to be round it doesn't qualify to be a planet, but Ceres and Vesta deserve it.

Re:Pluto controversy

[Anonymous Coward]

Yeah, it would be so much better to just refer to everything as "that thingy".

Re:Pluto controversy

[sznupi]

And this care haven't started, by chance, just after the recent decision about Pluto?

("deserve"? Yup, certainly doesn't appear to be emotionally driven, not at all... NVM that we have yet to establish with certainty that Vesta shape is due to hydrostatic equilibrium - and what about the Sun? It is big enough to be round too, was considered one)

Re:Pluto controversy

[jc42]

You don't find it significant that there are 8 bodies in the solar system that have a larger than 1000:1 ratio of their mass to the mass of other objects in the orbit ...?

Um, by that criterion, the Earth isn't a "planet" either. Its mass is only about 81.3 times the mass of a certain well-known object that shares its orbit about the sun. ;-)

There's also the observation that, strictly speaking, Jupiter isn't in orbit about the sun. The center of mass of the sun-Jupiter pair is outside the surface of the sun by a few thousand km. 44,000 km actually, which is only about 7% of the sun's radius. Jupiter orbits that point, or rather the nearby barycenter of the solar system.

There's a good wikipedia summary that includes numbers for the sun, Jupiter, and a few other important bodies.

Re:Pluto controversy

[mark-t]

I agree... I think reclassifying Pluto to no longer be a planet to be roughly equivalent to the scientific community deciding to rename atoms when it was first discovered that they were not the smartest particle.

But then, they never did that in the first place, so I'm really not sure why they felt it so necessary to do the former. Precise terms are useful, and it would be reasonable to assert that had the actual size of Pluto been realized when it was discovered, it would not have been considered a planet, much like atoms would not have been called thusly if it were initially known that they were not indivisible.

Re:Pluto controversy

[Chris Burke]

It's an observation, not a specific criterion, and you don't count direct satellites, because the moon is in orbit around the earth, not another object in an earth-like orbit around the sun (it is, but as a consequence of orbiting the earth). When the point is gravitational dominance of the orbit, the moon can hardly be counted against the earth which gravitationally dominates it now can it? Similarly Charon doesn't count against Pluto but it's still not even remotely close to gravitationally dominant.

Re:Pluto controversy

[m50d]

And this care haven't started, by chance, just after the recent decision about Pluto?

Nope. Happened as a kid, when I read my history of mathematics.

NVM that we have yet to establish with certainty that Vesta shape is due to hydrostatic equilibrium

So we need to learn more; not something I'd object to

and what about the Sun? It is big enough to be round too, was considered one)

It's big enough to fuse, which puts it in a different category. It's not history I care about, it's clarity of definitions, and I think the hydrostatic equilibrium one is a lot clearer to apply and more informative than this "clearing its orbit" notion.

Re:Pluto controversy

[sznupi]

Why not Pallas? Overall it's very similar to Vesta...

What about only "sort of fusing" sub-brown dwarfs? A random bit of mercury thrown out by an impact?

In the case of planets "clearing its orbit" is very informative, very revealing - as far as we can tell it is related to their origin, mode of their formation and evolution.

Re:Pluto controversy

[m50d]

Why not Pallas? Overall it's very similar to Vesta...

Not in hydrostatic equilibrium, is it?

What about only "sort of fusing" sub-brown dwarfs?

Sure, those are an edge case; it's not perfect.

In the case of planets "clearing its orbit" is very informative, very revealing - as far as we can tell it is related to their origin, mode of their formation and evolution.

Is it really? I don't know enough about this, maybe that definition is more useful than I thought then. Intuitively it seems like whether a planet cleared its orbit would be more of an "accident of history"; it's also much harder to test for a newly discovered planet. If it's associated with details about the composition etc., wouldn't it be better to define a planet in terms of these details?

still not a planet per the IAU

[heptapod]

Size does not matter. Clearing its path matters. Per the IAU Pluto has not cleared its orbital path and can not be considered a planet by the current definition.

Re:still not a planet per the IAU

[93 Escort Wagon]

Size does not matter. Clearing its path matters. Per the IAU Pluto has not cleared its orbital path and can not be considered a planet by the current definition.

Of course, the problem with this is - neither has Neptune.

Re:still not a planet per the IAU

[Anonymous Coward]

Or Earth, for that matter.

Re:still not a planet per the IAU

[gman003]

Satellites, like the Moon (or the ISS, even) count as "cleared".

Re:still not a planet per the IAU

[Anne_Nonymous]

>> Size does not matter. Clearing its path matters.

That's what she said.

Or something...

Re:still not a planet per the IAU

[sznupi]

The definition is not about vacuuming the neighborhood - bodies there (including Pluto) are completely dominated by the gravity of Neptune, that's what this is about.

Re:still not a planet per the IAU

[Mindcontrolled]

It's obviously not about complete clearing of the path, but rather of, well, dynamic dominance in his part of space. The planets do that, even if some orbit crossing or near orbit asteroids are left. Pluto and Eris are in a whole crowd of crap and have not in any way achieved a dominant position in that crowd of crap. In the end, it's just nomenclature

Re:still not a planet per the IAU

[blair1q]

And as long as the other planets are still there, Jupiter is not a planet.

Re:still not a planet per the IAU

[niado]

But Neptune (as well as Earth, and Jupiter) is clearly the dominant object in it's orbital area, dwarfing and gravitationally affecting everything else in the 'neighborhood'. Most planetary scientists are okay with this definition of 'clearing the neighborhood'.

Re:still not a planet per the IAU

[molo]

Please compare the total mass of all Neptune-crossing bodies to those gravitationally bound to Neptune. You will clearly find that Neptune has cleared the neighborhood. Neptune has a planetary discriminant of 2.4 x 10^4. A body with discriminant >= 1 is considered a planet.

-molo

Re:still not a planet per the IAU

[AnonymousClown]

So, as long as Pluto gives us pleasure, then it's size .....

Never mind.

Re:still not a planet per the IAU

[Tumbleweed]

Yes, let's come up with a definition that excludes Pluto - that way we can exclude Pluto. Makes sense.

Re:still not a planet per the IAU

[MozeeToby]

Don't forget the real reason that they wanted to change the definition in the first place: current theory predicts that there are probably hundreds, if not thousands of bodies in the outer solar system with basically the same composition and orbit as pluto, and only slightly smaller. There would be no logical reason to exclude those hundreds of bodies from the list of planets without also excluding Pluto, since there is little qualitative difference between them.

Re:still not a planet per the IAU

[Anonymous Coward]

Neptune has a planetary discriminant of 2.4 x 10^4. A body with discriminant >= 1 is considered a planet.

Your argument is ridiculous. You have countered an emotionally driven fact-free whine with pertinent scientific information. The correct response in this situation is either "Nuh uh!" or "Your mom!"

Re:still not a planet per the IAU

[Anonymous Coward]

Except that they don't orbit around the fucking sun!

Re:still not a planet per the IAU

[The_mad_linguist]

The real reason is because Bush was in office, and Pluto's the only planet discovered by someone from the USA.

The vote was held at the last day of the Europe-based conference, after most of the American astronomers went home from the location.

Re:still not a planet per the IAU

[sznupi]

I was just addressing the mentioned "issue" - but yes, exciting times (*) ahead, with many new discoveries almost certainly awaiting. My personal favorite at this point is Sedna, and not only because the timing (relative to its orbit) of the discovery hints at many such bodies - there's also some slight possibility it formed in another star system.

(*)Also because IMHO, if we will ever reach the stars, gradual spreading towards and across our Oort cloud (and eventually, after thousands of years, some groups hitching a ride in the clouds of passing star) seems like the way to go (though embryo colonization also looks practical)

Re:still not a planet per the IAU

[Anonymous Coward]

Your mom has a planetary discriminant of 2.4 x 10^4.

Will that do?

Re:still not a planet per the IAU

[Nadaka]

Apophis would like to have a word with you.

Re:still not a planet per the IAU

[geekoid]

actually, that was the reason they wanted a clear definition of 'Planet'. Pluto not being a planet is the results of those discussion, not the cause.

There would be nothing wrong if the definition included Pluto and all those other similar objects.

Re:still not a planet per the IAU

[Beardo the Bearded]

(*)Also because IMHO, if we will ever reach the stars, gradual spreading towards and across our Oort cloud (and eventually, after thousands of years, some groups hitching a ride in the clouds of passing star) seems like the way to go (though embryo colonization also looks practical)

The sky calls to us -- and if we do not destroy ourselves, we will, one day, venture to the stars.

Re:still not a planet per the IAU

[khallow]

A body with discriminant >= 1 is considered a planet.

Not by the IAU. As has been repeatedly mentioned before, the definition of "cleared the neighborhood" has not been defined by the IAU.

Re:still not a planet per the IAU

[butalearner]

Draw a dot, and eight concentric circles. The circles represent the orbits of the planets. Then draw an oval that touches the outermost circle on one end and goes out 2/3rds further on the other end. That's Pluto.

Below that, draw a straight line corresponding to the width of the circles. Those are the planets viewed edge on. Now draw a straight line tilted 17 degrees. That's Pluto.

Which of these is not like the other?

Re:still not a planet per the IAU

[John Hasler]

Pluto is not a satellite of Neptune and yet it crosses Neptune's path.

Re:still not a planet per the IAU

[John Hasler]

+5 Funny.

Re:still not a planet per the IAU

[slashdot_commentator]

And then there are other (non-IAU?) considerations, like:
Its not on the same ecliptic plane as the planets.
Pluto is not the central mass of its orbital plane. Charon does not directly orbit around Pluto; they both circle around the same point in space (along the orbit around the Sun).
Pluto has less mass than many planetary satellites (ex. Moon, Ganymede, Titan, Triton).
Pluto has no traits which differentiates it from the asteroids or KBOs.

Re:still not a planet per the IAU

[Jiro]

The way the technical definition of clearing the neighborhood is set up, Neptune does.

The real problem is that picking clearing the neighborhood in the first place is completely arbitrary. They could have picked "has an atmosphere" and ended up with Mercury being disqualified as a planet. They could have defined Jupiter as a failed star and disqualified Jupiter as a planet. They could have picked a size limit at Pluto's size and we'd have had 10 planets.

Re:still not a planet per the IAU

[bolthole]

Pluto has less mass than many planetary satellites (ex. Moon, Ganymede, Titan, Triton).

Mercury has less mass than Ganymede too. So.... it's just a "really big comet, in a very tight solar orbit"? :-)

Re:still not a planet per the IAU

[voss]

It would be funny if it werent at least somewhat true

http://www.chron.com/disp/story.mpl/nation/6557567.html

What is funny, is that 2500 scientists attended that convention but only 400 voted on that measure.

Re:still not a planet per the IAU

[Anonymous Coward]

actually, that was the reason they wanted a clear definition of 'Planet'. Pluto not being a planet is the results of those discussion, not the cause.

There would be nothing wrong if the definition included Pluto and all those other similar objects.

That may be true but it's naive to think that the motivation for defining "Planet" didn't color the discussion. The original parent is correct in that this was motivated by the perceived inconvenience of having a large number of bodies that would meet the definition.

The whole vote was a sham in my opinion, because there were other reasonable definitions that got suppressed in discussion because of the issue the parent is raising. The current definition is ridiculous and completely context-dependent, fuzzy, and completely colored by some emotional concern about how many planets there "should" be and how convenient it is for people to ennumerate them. I'd also point out that the hundreds of bodies that caused so much anxiety for so many people haven't become an issue.

Re:still not a planet per the IAU

[operagost]

While we're making arbitrary distinctions...

• Jupiter is not a planet because it's too much bigger than the other objects.
• Uranus and Saturn are not planets because they have rings.
• Saturn, Jupiter, Uranus, and Neptune are not planets because they're gaseous.
• Mercury's day is longer than its year.

Pluto has no traits which differentiates it from the asteroids or KBOs.

It's spherical. Some KBOs aren't, like my favorite Haumea. Yes, I'm an unscientific idiot.

Re:still not a planet per the IAU

[CorSci81]

The primary reason for the dwarf planet classification is the sane definition that would have made Pluto and similar bodies planets was based on having sufficient gravity to be spherical. That definition would have expanded the number of planets to a very large number with many of them being bodies in the asteroid belt. Having a planet being defined as a body sufficiently massive to clear its orbit kept the number of "planets" sane and has some practical connection to our current theories and understanding of the process of planet formation.

Re:still not a planet per the IAU

[CorSci81]

Definitions that are reasonable and include Pluto make the number of things we then have to call planets a rather large number. The current definition has some footing in our understanding of how planets form, which is that bodies like Pluto are essentially the remnants of areas of the solar system that failed to coalesce into planets, namely the Kuiper Belt and Asteroid Belt.

Re:still not a planet per the IAU

[Anonymous Coward]

Everything you disliked during his term is Bush's fault.

Re:still not a planet per the IAU

[christurkel]

If you put Earth out where Pluto is, it wouldn't clear it's orbit, either.

Re:still not a planet per the IAU

[John Hasler]

That's actually a fairly reasonable argument.

Re:still not a planet per the IAU

[riverat1]

What makes you think that?

Re:still not a planet per the IAU

[John Hasler]

Possibly because only 400 considered the issue of sufficient importance to hang around for.

Re:still not a planet per the IAU

[Merls the Sneaky]

No, if it was "completely dominated by the gravity of Neptune" it would have to be in orbit of Neptune.

Re:still not a planet per the IAU

[Merls the Sneaky]

So they changed the definition because it would be hard work to find all those objects? Fucking great science there.

Re:still not a planet per the IAU

[Merls the Sneaky]

While conveniently overlooking the fact Neptune hasn't cleared it's orbit of Pluto.

Re:still not a planet per the IAU

[Merls the Sneaky]

How would you prove that the "planet" cleared the neighbourhood and it wasn't cleared by another object that was lost due to other gravitational interactions. You can't! Making that definition of planet completely worthless.

Re:still not a planet per the IAU

[Merls the Sneaky]

So they made that definition because they are lazy? Hundreds of objects was too hard? Guess know I know why the decided not to become biologists I mean thousands of species! Think of all the work!

Re:still not a planet per the IAU

[IHateEverybody]

Don't forget the real reason that they wanted to change the definition in the first place: current theory predicts that there are probably hundreds, if not thousands of bodies in the outer solar system with basically the same composition and orbit as pluto, and only slightly smaller. There would be no logical reason to exclude those hundreds of bodies from the list of planets without also excluding Pluto, since there is little qualitative difference between them.

This has always bothered me. So what if we end up with hundreds or even thousands of planets? The planets of the inner solar system are vastly different (not to mention much smaller) from the Gas Giant planets. Yet there seems to be no great urge on the part of astronomers to create a new category to keep them separate from each other.

Re:still not a planet per the IAU

[sznupi]

It's in a f****ng 2:3 orbital resonance with it...

Re:still not a planet per the IAU

[CorSci81]

Neptune is more massive than every other body combined in its region of gravitational influence, that is typically what is meant by "cleared". Pluto and most of the Kuiper Belt Objects are in resonant orbits with Neptune, which is how they maintain the orbits they have. As another example you have the Trojan Asteroids that share Jupiter's orbit because they hang out in the Lagrange points.

Re:still not a planet per the IAU

[CorSci81]

The above poster summed it up. Learn orbital mechanics and then comment intelligently.

Re:still not a planet per the IAU

[DMUTPeregrine]

And the Perseids. Not cleared, Earth keeps running into the things.

Re:still not a planet per the IAU

[Anonymous Coward]

Earth because it has life, no Jupiter beause it has the most moons, no saturn because it has a hexagon on it, no mercury because its closest to the sun.

Re:still not a planet per the IAU

[Anonymous Coward]

Actually, Jupiter does have rings--they're just very faint, but they're there. :) In fact, if I'm not mistaken, I believe Neptune has rings too, but again--they're faint. So technically, that makes all the "gas giants" ringed planets. Whether you can easily see them or not. No doubt about it though, that Saturn has the most well-developed and easily-visible (not to mention most-studied) ring system and Uranus' rings appear upside-down and relatively simple.

Re:still not a planet per the IAU

[sunspot42]

Of course, the problem with this is - neither has Neptune.

The actual definition isn't "cleared it's orbital path". The definition is "clear the neighborhood around their orbits" by collision, capture, gravitational disturbance or establishing orbital resonances. Pluto/Charon has been yanked into an orbital resonance with the much more massive Neptune. While Pluto's orbit occasionally crosses that of Neptune, the dwarf planet never comes closer than 17 AU from the gas giant. In fact, it comes closer to Uranus (11 AU) than it does to Neptune.

Neptune is also vastly more massive than Pluto/Charon. The official definition looks at the mass of the candidate vs. the mass of all other bodies sharing that body's orbital zone. Here too, Pluto is stomped out of contention.

A large number of Kuiper belt objects, like Pluto, posses a 3:2 orbital resonance with Neptune. As with the asteroids Ceres and Vesta, Pluto/Charon is part of a population of like-objects, but those objects bear little resemblance to the 8 major planets of the solar system.

Re:still not a planet per the IAU

[sunspot42]

Mercury is more than twice as massive as Ganymede.

Mercury:
Mass - 3.3022 × 1023 kg
(0.055 Earths)

Ganymede:
Mass - 1.4819 × 1023 kg
(0.025 Earths)

Re:still not a planet per the IAU

[sznupi]

The sky calls to us...

I'm not sure how true even that will turn out - only some people end up, in one way or another, nomadic (Africa has the biggest genetic diversity, despite what some people might think because of appearances); but reaching the sky requires monumental amount of "right alignment" of factors. Perhaps even to the point of doing it before being replaced...

Re:still not a planet per the IAU

[sznupi]

They are most likely, as far as our current understanding of planet formation goes, very related. Those processes, in turn, are what gave them their orbits (hence also "cleared..." part). And those are things the Scattered Disk objects don't share.

Leave Pluto alone

[0racle]

It will always be a planet to me!

Re:Leave Pluto alone

[geekoid]

Is the world flat for you? does heavier then air flight exists in your tiny, stupid world?

Re:Leave Pluto alone

[SleazyRidr]

Did I miss the meeting where we decided that than is no longer a word and we should use then in its place? I've been seeing that one a lot recently.

Re:Leave Pluto alone

[John Hasler]

The IAU decided that, at the same meeting where they threw Pluto off the list of planets.

Re:Leave Pluto alone

[ultranova]

Is the world flat for you? does heavier then air flight exists in your tiny, stupid world?

Do you also ask these questions of people who classify spiders and insects together as "bugs"? Or do you reserve your strawmen solely for people who disagree with astronomers on what to call a frozen ball of rock over 4 light-hours away?

For the record, Eris will always be Xena to me.

To rephrase it...

[K. S. Kyosuke]

While everyone is more interested in the "mine is bigger than yours" aspect, the real science is the shockingly large density of Eris.

So, in other words, the question is not which one is bigger - Eris or Pluto, but which one is denser - Eris or the astronomers?

Re:To rephrase it...

[gman003]

Well, as soon as you figure out a simple, reliable and accurate method to figure out something's radius from 14 billion kilometers away, tell the astronomers.

Re:To rephrase it...

[nelsonal]

1. Fly 14 billion km measure, radio results back.




2. Continue flying for a few hundred years, then return in giant ship whose communications wreak havoc across your homeworld.

Re:To rephrase it...

[Valdrax]

So, in other words, the question is not which one is bigger - Eris or Pluto, but which one is denser - Eris or the astronomers?

Why the insults? Why are people so emotionally attached to the old order in which the term "planet" didn't have a solid, scientific definition which included Pluto (but in which kids didn't learn about similar bodies like Ceres) that they are willing to lash out at astronomers for attempting to put some kind of reason and order into the system?

I honestly can't think of any better demonstration of why humans should never achieve immortality. Look at how attached people are as minor of a belief that they were taught in childhood as whether or not Pluto is a planet. It's like the whole "debate" is a microcosm of how irrationally attached some people become to resisting change in their understanding of the world.

And people wonder why politics is so entrenched and partisan. If people can't adapt over Pluto just think of how stuck they are on the things that actually matter.

Re:To rephrase it...

[fnj]

There is this thing called a MAGNIFYING LENS (usually used as a collective system of same) which makes a distant object's apparent size large enough to measure its arc. Put a big enough one of those in orbit and your three qualifications are easily met. The one you don't mention - cost - might be a little problem.

Re:To rephrase it...

[gman003]

Not really. There's not enough light that far away from Sol to see much of anything. I tried to do the math, but it kept rounding to 0.

The other solution, waiting for it to transit another light source, is what just happened, and is not exactly an "on-demand" occurrence.

Re:To rephrase it...

[fnj]

Oops. My plan is undone. Now I need a really bright collimated light beam to reach out to it ...

Re:To rephrase it...

[K. S. Kyosuke]

Why the insults?

No insults, just an incredibly lame pun. ^_~

Re:To rephrase it...

[Surt]

How hard could it be to bounce a laser off of it for illumination?

Re:To rephrase it...

[John Hasler]

Very, very, very, very, very hard. Do the math.

Re:To rephrase it...

[riverat1]

Harder than bouncing a laser beam off of the nail on your left pinkie from the Moon.

Re:Judgment Day?

[maxwell demon]

Sorry, I cannot find anything about the relative size of Pluto and Eris at any of those places. Indeed, it seems the Bible doesn't mention either at all.

Eris?

[Anonymous Coward]

Its not been ten years since my astronomy studies... but Eris?
Thank god for wikipedia ( http://en.wikipedia.org/wiki/Eris_(dwarf_planet) )

Re:Eris?

[mbone]

I liked Xenia a lot better, and don't understand the sort of pedantry that disallowed it. Now it resides with the Brontosaurus in the land of cool, but abandoned, names.

If you want an odd body, look at Sedna, which may be a world from an alien solar system.

Re:Eris?

[Anonymous Coward]

Ugh, no thanks having it named after television's warrior princess. Might as well name a planet 'walmart' or something.

Fear not pluto-as-a-planet lovers, the ability to destroy a planet is insignificant next to the power of the force. That would be funny if demoting pluto was just a prank by anonymous.

Re:Judgment Day?

[Pojut]

I have done this, so can you read how the Bible says to be right with God

Is it just my observation, or is eldavojohn an idiot?

Uh...something doesn't seem right here...

Re:Judgment Day?

[Pojut]

Messed up quoting you, sorry about that. Still, I don't think quoting the bible and then shitting all over someone is going to help your cause...

Is a TURD in the cosmos!! Who cares !!

[Anonymous Coward]

If you think this is nerd news, you are not the nerd I thought you to be.

[Insert definition of planet]

[Anonymous Coward]

In my personal world, I've decided that a planet is something that's big enough to turn round due to its own gravity and isn't a star. Yes, including: moons, things not orbiting stars, Pluto and your mother.

All I want to know is...

[Bryan3000000]

Have they found the Black Lion, and is Princess Allura okay?

Oh, wait, that's Arus.

What does being old have to do with it?

[Valdrax]

Ask just about anyone geeky and my age,, and they'll telll you so: "yes, Pluto is a Fucking Planet, now stop trying to change things".

What does being geeky have to do with being old and too set in your ways to listen to reason?

Give us an argument why the IAU's definitions of a planet and of a dwarf planet are unreasonable. Please avoid any Appeal to Tradition. Also, can you craft a definition of a planet that covers Pluto but not Eris and Ceres other than "just what we used to arbitrarily call a planet?"

Re:What does being old have to do with it?

[The_mad_linguist]

How about that the IAU definition excludes "extrasolar planets" from being planets, on account of them not orbiting the sun.

Also, saying that "dwarf planets" are not a subcategory of the general category "planets" is just fucking stupid.

Re:What does being old have to do with it?

[CODiNE]

The reason that Pluto should be a planet is that

My Very Educated Mother Just Served Us Nine Pizza pies.

Re:What does being old have to do with it?

[Anonymous Coward]

Roundness should be the criteria.

If it is reasonably round then it has sufficient mass for gravitational collapse to 'pull it together' so; if it's round it should be a planet.

Also, I wish they had stuck with Xena instead of Eris, that’s what the discoverer originally called it and the bunch of "I'm an astronomer" snobs just did not like it.

Alas, everything is run by committee these days...

Re:What does being old have to do with it?

[Beardo the Bearded]

My definition is musical:

If it's not in the Holst suite, it's not a planet.

Re:What does being old have to do with it?

[Anonymous Coward]

... Also, can you craft a definition of a planet that covers Pluto but not Eris and Ceres other than "just what we used to arbitrarily call a planet?"

Why should we exclude Ceres and Eris? They be round, they be planets. Makes far more sense than current definition. Current definition is as arbitrary as "A planet is any Solar System body that can be resolved into a clear disk when viewing it through a cheap department store refractor."

Re:What does being old have to do with it?

[GlassHeart]

I fear you fail to understand the reason behind the "demotion." What we call it has never made any real difference in what Pluto does or does not do. The only use of these names is to help us understand them better. As such, the terrestrial planets share much in common, the gas giants share much in common, and Pluto shares little with either group. Thus, if you're saying that all Pluto-like objects should be called "planets", it would make some sense except that there are lots of them. If you're saying that Pluto alone should be a planet while similar objects are not, then that's a far less defensible position.

Re:What does being old have to do with it?

[res1216]

Earth?

Re:What does being old have to do with it?

[Valdrax]

How about that the IAU definition excludes "extrasolar planets" from being planets, on account of them not orbiting the sun.

Technically, the IAU definition only covers the distinction between bodies in our solar system and says absolutely nothing about bodies outside of it. This is because there is currently no way for us to determine whether or not any extrasolar planet clears its neighborhood (though we can probably guess for most of the Jupiter-sized ones).

It doesn't say that these bodies aren't planets. If just says that when defining bodies within our Solar System, "planets," "dwarf planets," and "small Solar system bodies" mean X, Y, and Z. It seems a practical compromise to avoid quibbling over questions we largely can't answer.

Also, saying that "dwarf planets" are not a subcategory of the general category "planets" is just fucking stupid.

Well, I would have preferred a different term to draw a greater distinction, but it does capture the fact that dwarf planets have part of the qualifications to be a planet: being large enough for their own gravity to keep them rounded.

Really it's the other way around in my mind since planets are just dwarf planets that are big enough to do something extra.

Re:What does being old have to do with it?

[Jiro]

My definition for a planet would be "big enough that scientifically interesting things happen on it that only happen on big objects".

So if it's got an atmosphere, different types of surface, weather, tectonic activity, etc. it's more planetlike. It's a sliding scale rather than a yes or no idea, and you'll probably need to come up with some size threshhold that roughly approximates this (since it's hard to tell if some newly discovered object, that you don't know anything about yet, has anything interesting on it), but I can't imagine Pluto failing this definition.

Re:What does being old have to do with it?

[khallow]

I fear you fail to understand the reason behind the "demotion." What we call it has never made any real difference in what Pluto does or does not do. The only use of these names is to help us understand them better. As such, the terrestrial planets share much in common, the gas giants share much in common, and Pluto shares little with either group. Thus, if you're saying that all Pluto-like objects should be called "planets", it would make some sense except that there are lots of them. If you're saying that Pluto alone should be a planet while similar objects are not, then that's a far less defensible position.

It makes sense, even if there are hundreds of Pluto-like dwarf planets. Let's point out the problems once again:

1) The IAU definition doesn't cover extrasolar planets. Hence, the definition is applicable to only one star system.

2) The IAU definition depends on the dynamics of the system, which can change. This is a weak quibble, but it is feasible on the time scale of millions of years for humanity to deliberately move planets and moons around. Even if nothing else happens, the Moon will become a planet in about a billion years just because the center of gravity of the Earth-Moon system eventually moves out far enough that it's no longer inside Earth.

3) The IAU failed to define "cleared the neighborhood". I know about the appropriate paper which spawned this choice of phrase, but I also know that the IAU didn't adopt that definition. Being a mathematician, I am aware of many other valid definitions of "neighborhood", some which would allow Pluto to be a planet and some which wouldn't.

4) As a result of the above ambiguity, the IAU had to explicitly enumerate the list of planets.

5) And for icing on the cake, we now have several bodies that aren't "planets", but are "dwarf planets". If I say that I have a dwarf star or a dwarf galaxy, then I expect a really small star or galaxy. I don't expect an object that is not of the general class. So why is a "dwarf planet" not a "planet"? It's bad grammar.

Re:What does being old have to do with it?

[Beardo the Bearded]

NOT A FUCKING PLANET.

Re:What does being old have to do with it?

[Trogre]

Fine, but just be aware that if tradition means nothing there could well be a redefinition of, say, moon. Since the barycentre of our Moon and Earth is (just) beneath the surface of the Earth, we're probably safe for now, but it wouldn't take much of a change in definitions to re-classify Earth-Luna as a double-planet system. Making the Moon, well, no longer a moon.

(not that I think Pluto should be re-instated as a planet - I realise it was only ever just America's "Look, we can discover planets too")

Re:What does being old have to do with it?

[Urkki]

1) The IAU definition doesn't cover extrasolar planets. Hence, the definition is applicable to only one star system.
 

Which is actually pretty smart. There are solar systems that we know are wildly different from ours (hot jupiters, massive apparently rocky planets). We don't really have a clue what kind of a universal definition of a planet would make sense and be a useful classification tool.

Better to refrain from making a universal definition of planet, until we have a lot more data points, having observed complete planetary systems around other stars. And that won't happen until we have either interstellar probes or solar system wide optical interferometers.

And looking at this one solar system, Pluto is clearly different from the first 8 proper planets, so for an analytical mind it's only natural to want to classify it differently.

Re:What does being old have to do with it?

[digitig]

How do you get "Kuiper Belt" from "pies"?

Re:What does being old have to do with it?

[c6gunner]

He obviously hasn't spoken with his Very Educated Mother

Re:What does being old have to do with it?

[Chris Burke]

1) The IAU definition doesn't cover extrasolar planets. Hence, the definition is applicable to only one star system.

That's a feature. They're expressly not defining "planet" in areas where we have little experience. That's vastly superior than arbitrarily guessing just because you hate non-universal definitions.

2) The IAU definition depends on the dynamics of the system, which can change.

Also a feature. It's been a long time since the universe was viewed as static and unchanging. Yes Luna could become a planet. So what?

3) The IAU failed to define "cleared the neighborhood". I know about the appropriate paper which spawned this choice of phrase, but I also know that the IAU didn't adopt that definition. Being a mathematician, I am aware of many other valid definitions of "neighborhood", some which would allow Pluto to be a planet and some which wouldn't.

I'm sure you could come up with a definition, but would it hit on any salient, obvious distinguishing features like the existing ones? Could you come with a definition of "neighborhood" that made Pluto a planet, but not Ceres or Eris? Or a thousand other objects? Maybe. But that would be a very precise and completely arbitrary definition.

Whereas there is a huge class of varying metrics by which it is flagrantly obvious that Neptune has cleared its neighborhood, and Pluto, Ceres, and Eris haven't even come close.

Not picking a specific one is, again, a feature because it leaves the door open for future observations which might indicate that one or another metric is more useful, rather than arbitrarily deciding today when just about any reasonable metric agrees with the IAU classifications.

Maybe it's because you're a mathematician that you feel every definition must be defined with infinite precision and universal applicability. But classifications in astronomy (and biology and geology etc etc) are rarely served by such definitions.

4) As a result of the above ambiguity, the IAU had to explicitly enumerate the list of planets.

It's only ambiguous because people like you said "Hey, I could define 'neighborhood' to mean 'within 5 angstroms of the surface' and then every particle of dust is a planet!" Yes, bravo for you. Anyway, here's what the obvious inference is when you decide to be reasonable.

So why is a "dwarf planet" not a "planet"? It's bad grammar.

I see you left the big guns for last. Guess what? It's not grammar, it's a name. "Pygmy chimpanzees" are not chimpanzees. Oh noes. Personally I think they adopted the term just to try to appease people by having the word "planet" associated in some way with Pluto. Not that this did any good, obviously.

Re:What does being old have to do with it?

[Jesus_666]

You failed both to capitalize "Pies" and to tell us what the tenth planet is. I hope it's made of pie.

Re:What does being old have to do with it?

[Anonymous Coward]

If it is reasonably round then it has sufficient mass for gravitational collapse to 'pull it together' so; if it's round it should be a planet.

So the earth's moon should be a planet?

Re:What does being old have to do with it?

[khallow]

That's a feature.

It makes the definition unusable for anything other than a narrow purpose (which would be better served merely by enumerating a list of planets), but sure, let's call it a feature.

I'm sure you could come up with a definition, but would it hit on any salient, obvious distinguishing features like the existing ones? Could you come with a definition of "neighborhood" that made Pluto a planet, but not Ceres or Eris? Or a thousand other objects? Maybe. But that would be a very precise and completely arbitrary definition.

Whereas there is a huge class of varying metrics by which it is flagrantly obvious that Neptune has cleared its neighborhood, and Pluto, Ceres, and Eris haven't even come close.

What's the scientific reason to say that Ceres and Eris aren't planets? If there are a thousand objects in the Solar System that are considered planets by the official definition, then so what? As to neighborhood here's a rival definition:

The neighborhood of a body orbiting around the Sun is the region of space closer to the object than 1/3 it's distance to the Sun.

Pluto (more accurately the Pluto/Charon pair) has cleared this particular neighborhood (aside from possible rare intrusions by Eris) to mass ratios which I believe comparable with Earth excluding its moon (though not the combined Earth/Moon system). It's a rather big region (almost reaching the orbit of Uranus, which is 11 AU in, which is why this particular number was chosen). Over time, it is a loci of Pluto's trajectory. And it doesn't have holes, unlike the hollow shell which presumably is the likely end state of the IAU's definition. In other words, unlike the IAU's apparent choice, this is a genuine neighborhood.

Sure, it is precise. Sure, it is arbitrary. But so was the IAU's choice.

Maybe it's because you're a mathematician that you feel every definition must be defined with infinite precision and universal applicability. But classifications in astronomy (and biology and geology etc etc) are rarely served by such definitions.

If that were true and if it were the argument I made, you'd be right. It's not though.

It's only ambiguous because people like you said "Hey, I could define 'neighborhood' to mean 'within 5 angstroms of the surface' and then every particle of dust is a planet!" Yes, bravo for you. Anyway, here's what the obvious inference is when you decide to be reasonable.

As I note above, 11 AU is a wee bit more than 5 angstroms.

I see you left the big guns for last. Guess what? It's not grammar, it's a name. "Pygmy chimpanzees" are not chimpanzees. Oh noes. Personally I think they adopted the term just to try to appease people by having the word "planet" associated in some way with Pluto. Not that this did any good, obviously.

When they realized that the pygmy chimpanzee wasn't closely enough related to the chimpanzee, then they did something about it. That's why they came up with a new name, "bonobo". Sure the old, confusing name is still used, but they are attempting to fix that. The IAU went the other way, sowing confusion with the term, "dwarf planet". As to the use of the term, "grammar", I merely aim for accuracy here.

Re:What does being old have to do with it?

[khallow]

Which is actually pretty smart. There are solar systems that we know are wildly different from ours (hot jupiters, massive apparently rocky planets). We don't really have a clue what kind of a universal definition of a planet would make sense and be a useful classification tool.

So what makes it smart?

And looking at this one solar system, Pluto is clearly different from the first 8 proper planets, so for an analytical mind it's only natural to want to classify it differently.

The four inner planets aren't particularly different. They only look different because they're a bit more massive and exposed for a few billion years to intense sunlight.

Re:What does being old have to do with it?

[Sethumme]

Clearly they should change the name from "dwarf planet" to "pseudo planet." Grammatically correct, pseudo planets would not be, in fact, planets at all, but merely similar to planets. As a bonus, I'm sure everyone could get behind the phrase "Pluto's a pseudo planet." Just try it out - it rolls off the tongue.

Re:What does being old have to do with it?

[Chris Burke]

My Very Educated Mother Just Served Us Nachos.

Re:What does being old have to do with it?

[arth1]

Well, both Ganymede and Titan are larger than Mercury. And tiny little Ceres is considered a dwarf planet.

Pluto is in a class of its own, as it's a binary system where the two bodies revolve around each other, and not one around the other.

My take on the whole thing is that the solar system has one star, two large planets, two medium sized planets, two small solids, and various debris (including moons, Mars, Mercury, Pluto, Eris, asteroids and comets).

If a body were to lose its planetary status, I'd pick Mercury. It doesn't have a noticeable atmosphere, it doesn't have any satellites, it's smaller than two of the moons, and its orbit is unstable and growing more and more elliptic.
Then Mars, which is a lot smaller than what most people think. It's not a twin planet to Earth, but only around a tenth of the mass and a seventh of the volume. And its moons aren't really moons, but orbiting oddly-shaped asteroids that'll never become spherical. Their presence is proof that it hasn't cleared its own orbit, which is one of the new criteria for being called a planet (and tailor-made to exclude Pluto, I might add).

Re:What does being old have to do with it?

[Anonymous Coward]

Really? As far as I know it's the planet with by far the most fucking going on.

Re:What does being old have to do with it?

[sunspot42]

If a body were to lose its planetary status, I'd pick Mercury. It doesn't have a noticeable atmosphere, it doesn't have any satellites, it's smaller than two of the moons

It may be smaller than two moons in our solar system, but it's far more massive than any of them. In fact I think it's more than twice as massive as the most massive moon, Ganymede.

Even Mars is only about twice the mass of Mercury.

its orbit is unstable and growing more and more elliptic.

Over a period of billions of years, perhaps. At the moment though, it's perfectly stable.

Then Mars, its moons aren't really moons, but orbiting oddly-shaped asteroids that'll never become spherical. Their presence is proof that it hasn't cleared its own orbit, which is one of the new criteria for being called a planet (and tailor-made to exclude Pluto, I might add).

Huh? Having natural satellites - or even Trojans - regardless of their shape is a characteristic which indicates that body has established at least some degree of orbital dominance. If you have stuff orbiting you then by definition you have orbital dominance over that stuff. Planets have the ability to clear virtually all of the mass from their orbits by collision, capture or gravitational disturbance, or to establish orbital resonances that prevent collisions. Dwarf planets can't manage that feat. It's a pretty simple definition, and one which interestingly enough automatically excludes not only Pluto, but all of the other icy junk we've found out past Neptune, plus all of the asteroids, which nobody has though of as planets for more than a century (although the larger asteroids were once too classified as "planets", until astronomers figured out they were part of a population of objects which had little in common with the other worlds we'd defined as planets).

The problem with calling Pluto a "planet" is that then the term "planet" isn't rendered terribly descriptive. If Pluto is a "planet" so are a bunch of asteroids and a slew of crap spinning around in the dark out past Neptune. A bunch of debris with characteristics which don't remotely resemble even bodies as small as Mercury, let alone worlds like Earth or Jupiter.

Re:What does being old have to do with it?

[MoeDrippins]

I'm being a dick here, but making a point. You say the definition is smart while simultaneously *NOT* using it correctly.

> There are solar systems ... rocky planets.

No, they're not planets. According to this "smart" definition.

Re:What does being old have to do with it?

[m50d]

Sure, why not? It has a lot more in common with Mercury than it does with Phobos. It's more useful to define bodies in terms of their own properties than where they orbit; if I were going to make a split amongst bodies that are large enough to remain spherical but didn't fuse, it would be between gas giants and rocky planets.

Re:What does being old have to do with it?

[Urkki]

Which is actually pretty smart. There are solar systems that we know are wildly different from ours (hot jupiters, massive apparently rocky planets). We don't really have a clue what kind of a universal definition of a planet would make sense and be a useful classification tool.

So what makes it smart?

Well, it's smart (or whatever word you want to use for "not stupid") only if you think definitions should reflect reality. If you prefer making definitions, and then trying to match reality to that, then there's no reason to avoid defining unknown, of course.

And looking at this one solar system, Pluto is clearly different from the first 8 proper planets, so for an analytical mind it's only natural to want to classify it differently.

The four inner planets aren't particularly different. They only look different because they're a bit more massive and exposed for a few billion years to intense sunlight.

Well, isn't volatile content of Pluto pretty high? Which means, there would be even less of it left it it was in the inner solar system and all the volatiles had evaporated...

But the biggest thing about Pluto not being a planet for me is, it's in 3:2 resonance with Neptune. IOW, it doesn't have independent orbit, it's orbit is controlled by Neptune. That doesn't sound very planet-like to me. A matter of opinion of course.

Re:What does being old have to do with it?

[Urkki]

I'm being a dick here, but making a point. You say the definition is smart while simultaneously *NOT* using it correctly.

> There are solar systems ... rocky planets.

No, they're not planets. According to this "smart" definition.

Planets of other solar systems are exoplanets, and calling them "planets" is just a colloquial short form.

Re:What does being old have to do with it?

[jc42]

Planets of other solar systems are exoplanets, and calling them "planets" is just a colloquial short form.

Pluto, Eris, and other similar objects outside the inner solar system are called "dwarf planets", and calling them "planets" is just a colloquial short form.

(I'm not sure how Ceres fits into this scheme. ;-)

Re:What does being old have to do with it?

[jc42]

It's more useful to define bodies in terms of their own properties than where they orbit; if I were going to make a split amongst bodies that are large enough to remain spherical but didn't fuse, it would be between gas giants and rocky planets.

True, That's most of why this discussion is so pointless.

Actually, it would probably be useful to also split the "rocky planets" into two distinct groups: Those with an atmosphere dense enough to have weather, and those without an effective atmosphere. In our solar syste, there are five such "rocky planets with atmosphere". In decreasing order of their atmosphere's density, they are Venus, Titan, Earth, Mars and Triton. Note that this is a rather different order than the order given by their masses, and only three of them are currently called "planet" by the IAU's definition. But it does make sense to have a term for those five, and a different term for the spheroidal rocky objects without air, which range from Ganymede down to Ceres, and maybe a bit smaller. (Or larger, depending what else we find out in the Kuiper Belt.)

Lessee, how many airless rocky (dwarf) planets/moons do we actually know of now?

Re:What does being old have to do with it?

[Urkki]

Planets of other solar systems are exoplanets, and calling them "planets" is just a colloquial short form.

Pluto, Eris, and other similar objects outside the inner solar system are called "dwarf planets", and calling them "planets" is just a colloquial short form.

(I'm not sure how Ceres fits into this scheme. ;-)

I'm actually fine with that, except when it causes confusion. Which is practically always. I mean, if you're asked to list planets, do you list exoplanets or dwarf planets (I mean, apart from maybe listing Pluto, if disagreeing with IAU definition).

Re:What does being old have to do with it?

[Chris Burke]

It makes the definition unusable for anything other than a narrow purpose (which would be better served merely by enumerating a list of planets), but sure, let's call it a feature.

Any definition is unusable for extra-solar systems because we can't see them well enough. Which is exactly why it's a feature not to try to make the definition apply to an area that is still largely unknown. Wanting to create a definition with the intention of it applying everywhere, even in the unknown, is foolhardy.

What's the scientific reason to say that Ceres and Eris aren't planets?

They haven't even come close to clearing their orbits.

The neighborhood of a body orbiting around the Sun is the region of space closer to the object than 1/3 it's distance to the Sun. Pluto (more accurately the Pluto/Charon pair) has cleared this particular neighborhood (aside from possible rare intrusions by Eris) to mass ratios which I believe comparable with Earth excluding its moon (though not the combined Earth/Moon system). It's a rather big region (almost reaching the orbit of Uranus, which is 11 AU in, which is why this particular number was chosen).

Exactly, you have to pic a fairly specific number to get that result. If you change it by 10% in either direction, the objects which do or don't apply will change drastically. But you pick the specific number that is required to get Pluto and not much else. With the IAU definition you don't need to draw such a specific, arbitrary line at all.

It's not that it's an inherently ridiculous definition. It's that there's no basis to say that narrow range of values is significant, while you're also deliberately avoiding looking at the huge and obvious gap between objects which have cleared their entire orbit thousands of times more. You're looking at only a small portion of the orbit, and a metric with large nmubers of examples in a broad range around it and no clear dividing line between.

Whereas looking at the entire orbit, there are 8 objects which are blatantly obviously different. You can't even try to deny that the difference isn't obvious between things that have cleared their entire orbit and those that haven't. The gap is huge.

So that's why your definition is not a good one. It is representative of no clear dividing line between planet and not-planet. The IAU definition undeniably targets a gigantic difference between the objects that apply and those that don't. Your metric sensitive to 10% variation, vs the IAUs 10,000x-tolerant metric.

The better definition is obvious -- it's the one where you can easily identify which planets match without having to quibble about the exact value. It's the one where, given no history of the objects involved and just a map of the known solar system, you can identify which ones are different.

Also, do you have a source for the nothing-in-11-AU metric? If you're just going by the orbits of known TNOs, then I wouldn't expect that definition to last for long. We're starting to discover more and more of them, and in the likely case that the mass in the Kuiper Belt is evenly distributed -- Pluto's meager gravitation is not going to force all the other objects to its lagrange points like Jupiter -- then we're going to find quite a few objects closer to Pluto. You'll have to (and, I'm sure, will) keep shrinking and shrinking your bubble to keep Pluto a planet.

But, you know, other than that, it's a decent definition.

it doesn't have holes, unlike the hollow shell which presumably is the likely end state of the IAU's definition. In other words, unlike the IAU's apparent choice, this is a genuine neighborhood.

No, the entire orbit, taken a as whole is a genuine 'neighborhood'. And I can't believe you're seriously arguing it's a problem that the good definition of neighborhood is a shell and therefore has "holes". Hello, the orbits themselves have "holes" in that sense. So... maybe make the definition match reality in som

Re:What does being old have to do with it?

[Chris Burke]

Erm, oops... Replied to the wrong post...

Re:What does being old have to do with it?

[Chris Burke]

It makes the definition unusable for anything other than a narrow purpose (which would be better served merely by enumerating a list of planets), but sure, let's call it a feature.

Any definition is unusable for extra-solar systems because we can't see them well enough. Which is exactly why it's a feature not to try to make the definition apply to an area that is still largely unknown. Wanting to create a definition with the intention of it applying everywhere, even in the unknown, is foolhardy.

What's the scientific reason to say that Ceres and Eris aren't planets?

They haven't even come close to clearing their orbits. And I don't mean within 10% like some definitions. I mean their orbits are thousands of times more cluttered than the objects that have cleared their orbits, creating a blatantly obvious gap.

The neighborhood of a body orbiting around the Sun is the region of space closer to the object than 1/3 it's distance to the Sun. Pluto (more accurately the Pluto/Charon pair) has cleared this particular neighborhood (aside from possible rare intrusions by Eris) to mass ratios which I believe comparable with Earth excluding its moon (though not the combined Earth/Moon system). It's a rather big region (almost reaching the orbit of Uranus, which is 11 AU in, which is why this particular number was chosen).

Exactly, you have to pic a fairly specific number to get that result. If you change it by 10% in either direction, the objects which do or don't apply will change drastically. But you pick the specific number that is required to get Pluto and not much else. With the IAU definition you don't need to draw such a specific, arbitrary line at all.

It's not that it's an inherently ridiculous definition. It's that there's no basis to say that narrow range of values is significant, while you're also deliberately avoiding looking at the huge and obvious gap between objects which have cleared their entire orbit thousands of times more. You're looking at only a small portion of the orbit, and a metric with large nmubers of examples in a broad range around it and no clear dividing line between.

Whereas looking at the entire orbit, there are 8 objects which are blatantly obviously different. You can't even try to deny that the difference isn't obvious between things that have cleared their entire orbit and those that haven't. The gap is huge.

So that's why your definition is not a good one. It is representative of no clear dividing line between planet and not-planet. The IAU definition undeniably targets a gigantic difference between the objects that apply and those that don't. Your metric sensitive to 10% variation, vs the IAUs 10,000x-tolerant metric.

The better definition is obvious -- it's the one where you can easily identify which planets match without having to quibble about the exact value. It's the one where, given no history of the objects involved and just a map of the known solar system, you can identify which ones are different.

Also, do you have a source for the nothing-in-11-AU metric? If you're just going by the orbits of known TNOs, then I wouldn't expect that definition to last for long. We're starting to discover more and more of them, and in the likely case that the mass in the Kuiper Belt is evenly distributed -- Pluto's meager gravitation is not going to force all the other objects to its lagrange points like Jupiter -- then we're going to find quite a few objects closer to Pluto. You'll have to (and, I'm sure, will) keep shrinking and shrinking your bubble to keep Pluto a planet.

But, you know, other than that, it's a decent definition.

it doesn't have holes, unlike the hollow shell which presumably is the likely end state of the IAU's definition. In other words, unlike the IAU's apparent choice, this is a genuine neighborhood.

No, the entire orbit, taken a as whole is a genuine 'neighborhood'. And I can't believe you're seriously arguing it's a problem that the good definition of neighborhood is

Rupert!

[dazedNconfuzed]

Rupert:

A planet in Earth's solar system beyond the orbit of Pluto. Rupert was named Persephone, but nicknamed Rupert after "some astronomer's parrot." It was eventually settled by the Grebulons.
In 2005, an actual tenth planet fitting Rupert's description was discovered beyond Pluto (which was considered a planet then, as opposed to a dwarf planet now). In a poll of the public conducted by New Scientist magazine to search out potential names for the object, "Rupert" ranked #5, and "Persephone" was the top choice. The planet was, however, ultimately named Eris.

obligatory

[groslyunderpaid]

the BIG YELLOW one is the SUN!!

Re:obligatory

[Tumbleweed]

the BIG YELLOW one is the SUN!!

It's not yellow.

Re:obligatory

[groslyunderpaid]

*sigh*

http://www.youtube.com/watch?v=ORTLn-RDnQ4 at ~2:32 to set the stage, and then

http://www.youtube.com/watch?v=DAZQ0qX5iR0 at ~1:33
 
Yeah, so...I wasn't really trying to accurately describe the color of the big yellow one...

Sick of this argument.

[TheRedDuke]

I thought the matter was settled when we learned it was a Mass Relay encased in ice.

Re:Sick of this argument.

[raitchison]

That isn't Pluto, that's Pluto's moon Charon.

Eris is more massive and may still be bigger

[mbone]

Don't give Eris out yet. There was a lot of discussion on the MPML about this.

First, Eris is definitely more massive, by about 28%. They both have satellites with good orbits, so their masses are pretty well determined.

Second, it is not really that clear that Pluto is really larger than Eris. There have been a number of estimates of Puto's size; by the most recent one presented by Angela Zalucha at the DPS meeting (a radius fit to occultation measurements with a new atmospheric model), Pluto and Eris have roughly the same radius within the respective error bars (1146 +-20 km in diameter for Pluto versus 1170 km for Eris).

What is more interesting to me is that Eris is dense and very bright - could something as rare as Deuterium snow be covering its surface ?

Re:Eris is more massive and may still be bigger

[Genrou]

Isn't it fitting that Eris is the goddess of chaos?

Re:Eris is more massive and may still be bigger

[mbone]

I like the first name, Xenia, much better.

Re:Eris is more massive and may still be bigger

[Anonymous Coward]

Better yet... could it be covered by di-lithium?

Re:Eris is more massive and may still be bigger

[Anonymous Coward]

I suppose we'll have a pretty damn accurate estimate of the radius of Pluto in mid-July, 2015. It's almost unreal to think we'll have close measurements and pictures of such a distant body. Shame we can't afford to send more probes. Imagine if NASA would have produced a handful or two of New Horizons and launched them in various directions to scout all the newly discovered bodies...

I wish there were more science nerds in government.

Re:Eris is more massive and may still be bigger

[Luke has no name]

Random fact, crazy-fascinating but purely-speculative question: Your last sentence shows you'd be good at writing Slashdot summary endings.

What I first thought it said

[david.emery]

I glanced at my RSS feeds and thought the story title was "Pluto might be bigger than Elvis". Now that would be really big!

Re:What I first thought it said

[by (1706743)]

Let's just hope Pluto doesn't die on the cosmic crapper.

I'm not even sure what that means.

Re:What I first thought it said

[John Hasler]

It means that whatever is that your smoking, I don't want any.

Who decides what the definition of "planet" is?

[Caerdwyn]

Who decides what the definition of "planet" is?

The IAU, not Walmart-denizes with a microphone shoved into their face, nor IT workers who read something on Wikipedia once. There is no "wobbly ground", and the IAU doesn't answer to the general public.

Besides. If Pluto fits the definition of "dwarf planet", how does the size, existence, density, or any other property of Eris change whether Pluto fits the definition?

Re:Who decides what the definition of "planet" is?

[geekoid]

cause they get more hits by bringing up the manufacturversy.

Re:Who decides what the definition of "planet" is?

[Anonymous Coward]

Who decides what the definition of "planet" is?

The IAU, not Walmart-denizes with a microphone shoved into their face, nor IT workers who read something on Wikipedia once. There is no "wobbly ground", and the IAU doesn't answer to the general public.

Sez who? The IAU? Last time I looked the use of a word was defined by how it is used. If the entire world except for a handful of astronomers calls Pluto a "planet", guess what - it's a planet.

Re:Who decides what the definition of "planet" is?

[John Hasler]

> Who decides what the definition of "planet" is?

Everybody. We argue about it, use various conflicting definitions for a while, and eventually converge on a consensus. That's how natural language works.

> The IAU... ...determines what definition will be used in IAU publications. Their definition is influential but not necessarily dispositive.

Re:Who decides what the definition of "planet" is?

[Surt]

Actually, it's the general public that decides the definition of planet, not the IAU. The general public wins because they have the most votes and weapons if it comes down to either democracy or war over it. So get used to it: Pluto is a planet.

Re:Who decides what the definition of "planet" is?

[readyou.txt]

Who decides what the definition of "planet" is?

All interested parties, whether they are technically informed or not. See "Hacker" "Cracker" controversy.

Re:Who decides what the definition of "planet" is?

[Anonymous Coward]

Who decides what the definition of "planet" is?

The IAU

Except that "planet" has been an English word for centuries before the IAU existed.

Re:Who decides what the definition of "planet" is?

[PieSquared]

I think the editor is mixing up "impetus for discussion about the definition of planet (which ended up excluding Pluto)" with "reasons for the final definition of planet (which excludes Pluto)".

What actually happened was: we discovered Eris, and the IAU said "huh. It seems likely that there are hundreds of objects large enough that we'll have to decide if they're planets, where before everything we found was clearly either a planet or an asteroid/comet. Not to mention all these planets we're finding around other stars... We need a good definition of planet to go forward with." The final definition agreed upon excluded Pluto.

What the editor appears to believe happened is: we discovered Eris, and the IAU said "huh. This is bigger then Pluto, so either both are planets or neither are. We don't want to increase the number of planets, so lets go with 'neither'."

At least, I don't see any reason why someone might think an adjustment to the size of Eris would cause a reconsideration of Pluto as a planet unless something like the second was what happened.

Re:Who decides what the definition of "planet" is?

[Chris Burke]

In fifty years, your grand kids will learn in school that there are 8 planets, and many smaller objects in the asteroid and Kuiper belts.

And when Grandpa says "Hogwash! Pluto's a planet dag nabbit!" they'll just roll their eyes.

Re:Who decides what the definition of "planet" is?

[petermgreen]

All depends what education authorities do. If they decide to follow the IAU (which is likely as afaict there is no other organsation of similar standing pushing a rival definition) then that is what kids will be taught.

Re:Who decides what the definition of "planet" is?

[Anonymous Coward]

Except that "planet" has been an English word for centuries before the IAU existed.

... so you want to go back to five planets?

MVEMJSUNP

[AgentPhunk]

Many
Very
Educated
wo(M)en
Just
Saved
Unfortunate
Ninth
Planet

The Definition of Planet Will Change Yet Again...

[Philomage]

...Once we conquer gravity and develop some sort of gravity drive that doesn't require half a universe's worth of energy to lift off out of a gravity well.

A planet then will be something we can land on, and walk around upon, that is the most significant gravity well in easy distance.

This significantly matches the science fiction (fantasy fiction?) concept of what a planet is...

Re:Judgment Day?

[Nadaka]

It seems perfectly acceptable for a religion that advocates the murder by magical bears of 42 children for the sin of pointing at a man, laughing and calling him bald.

Re:Judgment Day?

[Anonymous Coward]

Do you respond to such obvious trolls purely for the sake of getting more hits on your sig? Smidge207's posts are hardly interesting enough to merit 2 replies.

Re:The Definition of Planet Will Change Yet Again.

[raodin]

I'm sorry, but your definition of planets has gaping hole. Unless you believe that gas giants shouldn't be classified as planets?

Pluto is just a comet

[Albinoman]

Pluto is mostly made of various ices (like comets) and travels through the Oort Cloud (like comets). It's orbit is highly eccentric and at a tilt (like comets). Pluto is quite clearly a large comet that never made it to the inner Solar System. Also, because of it's companion, Charon, the center of gravity for the two is actually between the two. If it were a planet, it would also be unique in this respect as well.

Bowser's planet

[tepples]

If it's not in the Holst suite, it's not a planet.

In other words, King Koopa's airship is a planet. Seriously: play "Mars" and then the Airship theme.

Re:Bowser's planet

[WWWWolf]

If it's not in the Holst suite, it's not a planet.

In other words, King Koopa's airship is a planet. Seriously: play "Mars" and then the Airship theme.

But it's a widely known fact that quite a bit of Warcraft soundtrack was inspired by Mars. Oh, darn. Azeroth is a real planet? Do I need to start playing that ridiculous newfangled Internet game?

Eris == Kobold ?

[_bulbgiver_]

That protector of ours, Brennan-Monster is at it again !

Oops, Kuiper Belt, not Oort Cloud

[Albinoman]

nt

Why do we need a definition?

[Estanislao Mart�nez]

Give us an argument why the IAU's definitions of a planet and of a dwarf planet are unreasonable. Please avoid any Appeal to Tradition.

The definitions are unreasonable because no definitions are needed. Nature makes no distinction between "planets" and "dwarf planets." Celestial objects don't split into neat discrete types either by trajectories or composition or any other criterion. They all follow the same laws of physics. There's no separate sets of physical laws for the motion of planets and that of other objects (which is, by the way, the reason the ancients gave the "planets" a distinctive word to distinguish them from other "stars" (in the original sense)).

Basically, "planet" is an obsolete category that no longer does any work in astrophysics. You can exhaustively state everything that we can state about a celestial object without settling the non-issue of whether it's a "planet" or not.

Also, can you craft a definition of a planet that covers Pluto but not Eris and Ceres other than "just what we used to arbitrarily call a planet?"

Of course, since celestial objects differ from each other in degree on a large number of criteria. The only definitions of any interest is the traditional one—on account of being traditional. Stop pretending that we're making some sort of scientific progress by pointlessly redefining a term that's just not useful anymore. Leave the damn definition alone as a reminder of how we got to where we are today.

Re:Why do we need a definition?

[John Hasler]

Mod parent up.

What I want to know is...

[Anonymous Coward]

What is Eris? Seriously, I have never heard of it? Is it far away? Close?

Re:What I want to know is...

[petermgreen]

http://en.wikipedia.org/wiki/Eris_(dwarf_planet)
"Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly. It is estimated to be approximately 2300-2400 km in diameter,[14] and 27% more massive than Pluto or about 0.27% of the Earth's mass."

It is the object that finally lead to pluto's "demotion" from planet to dwarf plant.

definition

[iccaros]

I thought the definition of Dwarf Planet was: Large Enough to be round (that is enough mass to create a Spheric shape). Both meet this requirement even if Pluto is bigger Orbit the Sun. Only Pluto Have a clear Orbit no on Pluto and no on Eris Ceres is the only other object that is unquestioned as a Dwarf Planet. If Pluto is seen as bigger than Eris, then given that it is dose not have a clear orbit for as much as I know.. which is not much, means it should not be listed, or never should have been, as a Dwarf Planet.

classic definition

[hort_wort]

I think the word "planet" comes from a Greek word meaning "roaming star". This was assigned to stars that seemed to move in a direction different from the other stars in the sky. So if you want to really think of the classic definition, Earth isn't a planet either. ^.^

(I remember reading about the sphere thing, also. That one sounded good to me.)

If we are not Animal, ...

[TimSSG]

If we are not Animal, then are we Plant, Fungi or Mineral? I know a few people that might count as Fungi. Tim S.

"the shockingly large density of Eris"...

[ridgecritter]

My money is on Scrith.

The goddess of discord

[Mspangler]

The goddess of discord is certainly living up to her reputation.

"So you think you have me all figured out, do you? Heh, heh, heh."

So how long will it take to get there, how big of a dish will it take to get a signal back, and how much plutonium to power the instrument package and radio to find out what is really going on out there?

Stop Calling Them Planets Re:Pluto controversy

[IHateEverybody]

Maybe the term "planet" has just outlived its usefulness. It's an overly broad and difficult to define category of celestial objects. Maybe it's time to invent some new nomenclature. I give you our new solar system:

Mercury, Venus, Earth, and Mars will now be known as Rocky Planetary Objects (RoPOs).

Jupiter, Saturn, Uranus, and Neptune will henceforth be known as Large Gaseous Objects (LaGOs).

Any objects which are smaller than Mercury but large enough to compress itself into a sphere will now be called Quasi-planetary Small Objects (QuaSOs).

You're welcome IAU.

Re:The Definition of Planet Will Change Yet Again.

[IHateEverybody]

I'm sorry, but your definition of planets has gaping hole. Unless you believe that gas giants shouldn't be classified as planets?

We could call them Dwarf Brown Dwarfs. Or since they are after all giant gasbags, Politicians.

IAU planet definition is pure junk

[syousef]

When the difference is a factor of 10,000, there's absolutely no need to create a precise definition, and it would be foolish to do so.

Well if the IAU was going for an IMPRECISE definition they couldn't have done better. Science is all about definitions. Precision is important. The current definition is an utter mess. I couldn't care less that Pluto was named after a Disney character. If we want to be precise it belongs in a different category BUT

1) They created pair of definitions where a "dwarf planet" is not a "planet. That is confusing and ridiculous.

2) They mention "the sun" and therefore the definition as written excludes extrasolar planets. So now we have "dwarf planets" that are not planets and "extrasolar planets" that techincally also are not planets.

3) The clearing the path part of the definition is an arbitrary requirement and a kludge. It is possible we will discover extrasolar planets that cross each other's orbits in a stable way. Fortunately extrasolar planets aren't planets anyway.

There are other things wrong with the definition, but lets just leave it at that shall we? The definition is beauracratic and in terms of science it is PURE JUNK. Science is about understanding things. We humans do this by classifying them, so definitions are important. However in this case everyone was more focused on whether or not Pluto is a planet and was bending the definition to fit their preference.

Re:IAU planet definition is pure junk

[Anonymous Coward]

Science is about understanding things. We humans do this by classifying them, so definitions are important. However in this case everyone was more focused on whether or not Pluto is a planet and was bending the definition to fit their preference.

And? There's a problem?

That IS how we define things: we look at them and examine them, and according to what we know we say 'this thing is sufficiently similar to that thing, so we'll say they belong in the same class'. The astronomers in the 1930's did this, and called Pluto a planet because it seemed to them that it was. Now we know much more about it, and it obviously is very different from all the other objects we call planets, so let's stop calling it one.

When Linnaeus first started classifying living things, he did it by comparing their physical characteristics and lumping similar things together, and at the time that seemed to make sense. Later we decided (quite arbitrarily) to classify plants and animals by their genetic descendance instead, and taxonomies were all shook up. Boo hoo.

Sure, the definition of a 'planet' could be better, but it's still better than no definition AT ALL, which is what we had before. And don't worry, it will no doubt be revised in the future, lots of times.

Re:IAU planet definition is pure junk

[syousef]

Sure, the definition of a 'planet' could be better, but it's still better than no definition AT ALL, which is what we had before. And don't worry, it will no doubt be revised in the future, lots of times.

No definition at all is MUCH better than an incorrect, imprecise, politically driven definition.

Re:IAU planet definition is pure junk

[jc42]

Sure, the definition of a 'planet' could be better, but it's still better than no definition AT ALL, which is what we had before. And don't worry, it will no doubt be revised in the future, lots of times.

No definition at all is MUCH better than an incorrect, imprecise, politically driven definition.

Well, now; that depends on what you think the motive for the (re)definition might have been. One possibility was that they were just trying to tweak us, and if so, they certainly succeeded. And further support for this can be found to talking to a few astronomers, who mostly react to the topic by grinning.

Let's face it, "planet" is not exactly what you'd call a technical term. All it really ever meant was (first) that it wandered around in the Earth's sky, rather than following a fixed path like the stars did; then (second) wandered in an orbit around the sun; then (third) orbited around a star-like object but wasn't another star. This is far too vague a concept to be of much value, other than to refer to "a big object in orbit around a star".

A precise definition isn't really needed for any technical reasons, because when you get to the point of wanting to distinguish, say, Jupiter from Luna or Titan or Ganymede, there are better terms available. Or you just name the object and list its numbers. Which "bin" it belongs in isn't all that useful, especially from one bin includes Jupiter and Mercury, but not Ceres or Titan, which are in a different bin.

Granted, some astronomers have put a rough lower bound to a planet's size, mostly that it should be approximately spherical. But that's also vague and fuzzy. The Earth has bumps several km high, so does that make it lumpy enough to not be a planet? Obviously not, so how out of round can a "planet" be? No astronomer has ever really said. Ceres certainly looks round in low-res photos, though we got pictures good enough nearly a century ago to decide that it was too lumpy. But some astronomers still refer to Ceres as a planet, probably just to tweak the rest of us. Others suggest that the Earth/Luna pair should be called a double planet in the same solar orbit. Nothing much ever seems to have come of this, though, so it's probably also just to tweak us (and perhaps also other astronomers).

The demotion of Pluto from an unmodified "planet" to a modified "dwarf planet" does seem to have set off the sort of legalistic dispute that is usually reserved for theological and political discussions. This is further support that the redefinition was intended to be entertaining, rather than anything really significant from a scientific viewpoint. The way that actual astronomers just ignore the issue (and grin) is further evidence that they don't consider it anything serious that applies to them.

So continue your debate over this vexing "scientific" issue. Meanwhile, most astronomers will be off doing science and not wasting their time with such silliness. And using actual scientific terminology in their reports, except when they want to be vague and fuzzy because the data has large error bars.

Re:IAU planet definition is pure junk

[syousef]

For pity sake. Classification is fundamental to science, and the word "planet" appears in plenty of the journal articles I've read on Arxiv when I was doing my astronomy degree. SO the whole idea of dismissing this as a non-technical term that doesn't matter is ridiculous.

For a lot of people THIS kind of illogical nonsense - scientists making up stupid definitions that make no sense by committee - is their one of their ONLY exposures to science and they never see it beyond high school level. Every high schooler will be exposed to this debate, whether or not they aspire to become scientists.

This is one reason science is not taken as seriously or given funding. The public see scientists who do this kind of thing as propeller heads that are completely divorced from reality. Is it any wonder they don't want to vote for politicians who'll give these scientists money. It's not the only reason by any means but it is significant. Any scientist grinning at giving people a valid reason to be dismissive of science is a moron and fits the unfortunate stereotype of lacking people skills. Contrary to the saying, not all publicity is good publicity either. A lot of people have been put out by the fact that their pet planet is no longer a planet. So they, though less rational, are also likely to hold a grudge and consider big science a waste of money.

One more thing - the part of the definition requiring that a planet be roughly spherical is not as bad as you seem to think. There definitely is a continuum. But you could define things very precisely if you required a measurement of the deviation from spherical and allowed for flattening due to rotation or presence near a larger body. The definition of course doesn't do that but that is because it is, as I said PURE JUNK, not because it can't be done.

Re:IAU planet definition is pure junk

[jc42]

For pity sake. Classification is fundamental to science, ...

Of course. But classification by itself isn't necessarily scientifically useful. The criticisms of the current IAU definition "planet" as "junk science" are examples of this. An incorrect classification is sometimes not just useless; it can impede understanding.

A historic example was the 17th-century debate over "momentum" versus "impetus", which had similar definitions with subtle differences. Newton effectively showed that "momentum" was the correct term, and "impetus" was dropped from scientific terminology (though it's still around in common English speech and writing). The difference might be subtle, but it's important. If you confuse the two, you can't understand basic physics correctly.

A major recent example of this is the success (over the course of successful decades) for the "cladistics" approach in the biological sciences. This is a purely classification concept, and is based on the idea that the only valid classifications are the ones based on common descent. A common textbook example is the term "invertebrate", which is bogus because it's not a complete evolutionary group. It excludes a subset, the vertebrates (which is a valid classification). If you think "invertebrate" is a valid classification, you have a serious misunderstanding of basic biology. It's useful as an informal description, but it's not a classification.

One of my favorite examples is to remark that humans are a species of fish. This mostly gets me funny looks, except among biologists who typically say something like "Of course". We are descended from fish, and if your definition of fish excludes humans, your definition is bogus and impedes your scientific understanding.

A more common example is that the term "ape" must include humans to be valid. This is, of course, rejected by most of humanity, especially the religious types. But we are descended from apes, so that term must include us to be of any scientific value.

The current term "planet" is a nice example of a similarly bogus scientific classification. A small group of publicity-minded astronomers basically decided that they want a term for the publicly-memorable set of big objects that orbit our sun, and made up a convoluted definition that works for that purpose. But the result is just a PR term, of little if any value for any scientific purpose. Yeah, you see "planet" in some scientific writings. You see a lot of informal terms. But all it really means is "a big object that's not a star". When they want to say more about it, they drop the term, and talk about the details.

Biologists figured out that the popular exclusion of humans from such terms like "ape", "fish" and "animal" results in a bogus classification, and define all those informal terms in a way that includes humans. For astronomers to define a term that includes Jupiter and Mercury while excluding Ganymede, Titan, Ceres and Pluto is equally bogus. It's just embarrassing that they would do such a thing in our supposedly modern, scientifically enlightened age.

Yeah, I understand why that small group might make such a definition. But I find it embarrassing, even if I'm not an astronomer. They should just publicly wash their hands of the term, and let the media deal with it. Or define it as "big thing that isn't a star". Like other bogus semi-scientific terms, it leads to public misunderstanding. And it wastes our time with discussions like this, which shouldn't be necessary in a supposedly technically-oriented forum.

Re:IAU planet definition is pure junk

[syousef]

Of course. But classification by itself isn't necessarily scientifically useful. The criticisms of the current IAU definition "planet" as "junk science" are examples of this.

Talking to you is like talking to someone on a 10th grade debate team. You flap your lips without any regard for logical consistency, just so long as what you say puts forward an counterpoint.

First of all I haven't put forward a scientific definition. I've put forward an opinion on a scientific definition being sub-standard on a message board. There is no subtlety about the difference between these 2 things. One is a working definition and must be held to a high standard. The other requires no such scientific rigour.

An incorrect classification is sometimes not just useless; it can impede understanding.

A historic example was the 17th-century debate over "momentum" versus "impetus", which had similar definitions with subtle differences. Newton effectively showed that "momentum" was the correct term, and "impetus" was dropped from scientific terminology (though it's still around in common English speech and writing). The difference might be subtle, but it's important.
If you confuse the two, you can't understand basic physics correctly.

Thanks for the irrelevant history lesson. Would you make your mind up please? Is "planet" a scientific term that should be defined correctly, or is it just a popular term that does not need to be defined correctly? Just what is your viewpoint on this.

I can't help but laugh at the irony of your use of Newton's definition of momentum, given that Newtonian physics has been shown as nothing but a very good approximation at the speeds we humans are use to dealing with.

In any case, I am not trying to do science. I am pointing out that science has been done in a sub-standard way.

A major recent example of this is the success (over the course of successful decades) for the "cladistics" approach in the biological sciences. This is a purely classification concept, and is based on the idea that the only valid classifications are the ones based on common descent. A common textbook example is the term "invertebrate", which is bogus because it's not a complete evolutionary group. It excludes a subset, the vertebrates (which is a valid classification). If you think "invertebrate" is a valid classification, you have a serious misunderstanding of basic biology. It's useful as an informal description, but it's not a classification.

One of my favorite examples is to remark that humans are a species of fish. This mostly gets me funny looks, except among biologists who typically say something like "Of course". We are descended from fish, and if your definition of fish excludes humans, your definition is bogus and impedes your scientific understanding.

A more common example is that the term "ape" must include humans to be valid. This is, of course, rejected by most of humanity, especially the religious types. But we are descended from apes, so that term must include us to be of any scientific value.

Another history lesson. I get it. You've read science history. But again your point isn't relevant. If a scientific definition is logically consistent but goes against intuitive lay thought, that is not a problem so long as there is a very good reason for it. If the definition isn't logically consistent ("JUNK") then there is a problem. If for example humans were specifically excluded from the definition of "fish" but apes were not, I'd have a problem.

The current term "planet" is a nice example of a similarly bogus scientific classification. A small group of publicity-minded astronomers basically decided that they want a term for the publicly-memorable set of big objects that orbit our sun, and made up a convoluted definition that works for that purpose. But the result is just a PR term, of little if any value for any scientific purpose.

All hail Eris!!!

[Anonymous Coward]

All hail Eris!!!

Dwarf Planets are Planets Too

[laurele]

The battle over the status of dwarf planets has never subsided. Pluto and Eris are both planets and Kuiper Belt Objects. One does not preclude the other. They are planets because they are large enough to be rounded by their own gravity. They are Kuiper Belt Objects because they are located in the Kuiper Belt. Ceres too is a small planet because it is large enough for its gravity to pull it into a spherical shape. The IAU misappropriated the term "dwarf planet," which was first coined by Dr. Alan Stern, Principal Investigator of NASA's New Horizons mission to Pluto, to indicate a third class of planets which are large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. He never intended for "dwarf planets" to be classed as not planets at all. The IAU did not "have" to do anything other than allow Eris's discoverer to name it while holding off on any additional classification until more information is discovered about remote planets in this solar system and all planets in other solar systems. Significantly, there are quite a few exoplanet systems in which multiple planets orbit the host star in various different planes. Some have orbits far more eccentric than Pluto's, yet they are giant planets the size of Jupiter or larger. According to the IAU definition, none of these objects are planets! Saying there are more differences between Pluto and the eight closer planets to the Sun depends on what aspects one considers. Earth actually has far more in common with Pluto than with Jupiter. Both have surfaces on which we can place rovers and landers. Both have a large moon formed by giant impact; both are geologically differentiated into core, mantle, and crust, and both have nitrogen in their atmospheres. Other than orbiting the Sun, what do Earth and Jupiter have in common? It is premature to pronounce declarations that these faraway objects are definitively not like the other planets or that one is larger than the other. We just do not have enough data at this point to do more than make educated estimates. What we really need to do is send robotic missions like New Horizons to Eris as well as Haumea and Makemake. Yes, that will take time and money, but it is a far better investment than the black holes the endless wars in Iraq and Afghanistan have become. Also, memorization is not important. It is much more important to teach the characteristics of each category of planet than to ask kids to memorize a bunch of names. We don't ask them to memorize the names of rivers or mountains on Earth, so why do so with planets, and why allow a need for convenient memorization to determine how we classify them?

there is a simple solution to this problem...

[dotar]

Simply do away with the term "planet" as an astronomical term, and refer to everything out there as a "class [x] celestial body".

Re:The Definition of Planet Will Change Yet Again.

[Philomage]

Actually, failed stars was more my vote, but yes, it was an intentional gap.