Talk:Definition of planet/Archive 1

message: After having been working on the Planet article on and off for a long time, it occurs to me that there is a much better "definition of planet" section there than here. If somebody could find the time, could they add some (or all) of that information here? This article is severely lacking by comparison.
_________________________________________________________________________
Actually, there really isn't a lot of information in that article that isn't here; it's just arranged differently. The "planet" subsection begins by mentioning the debate (still unresolved) convened by interested parties of the IAU, which is also mentioned at the head of this article. It then proceeds to say that the consensus they were arriving at was:
"A planet is a body that directly orbits a star, is large enough to be round because of self gravity, and is not so large that it triggers nuclear fusion in its interior."
All three of these criteria are mentioned in the article; the first two are mentioned just under the "issues and controversies" heading, the last is mentioned near the end of the "minor planets" section. That consensus definition, it appears, was illusory and news is that the IAU group are no closer to a resolution than before. Indeed the first "official" declaration by the group was completely different from the one listed in the "planet" section, so for now, until they make the truly final statement on the matter, it seems best to leave such speculation out. 
The next section deals with the differences between planets and brown dwarfs, which is the topic of the third subsection of this article. Gibor Basri's definition is not really any different than the one mentioned above it. Although his work is phenomenal and this article has links to his essays on the subject, it seems premature to give credence to any one definition or theory until the final word is in from the IAU. However if you feel that this information could be better-arranged, please feel free to suggest alterations. Serendipodous 21:11, 21 December 2005 (UTC)
thread_title: Improvements

message: I consider much faster Pluto as a planet than Jupiter, Saturn, Uranus or Neptune. For me a planet is a sizable mass that is so big that it starts to appear as round, and where we can land :D. My def is much better than that of those lunatics that say Jupiter is a planet and Pluto is not. A Xanax would solve their problem. -Pedro 18:40, 1 May 2005 (UTC)
replies: text: Pluto is not faster than Jupiter; in fact it is far slower, because it is much further out. The further a planet is from a star's gravity, the slower it moves. Yes, being round is one criterion that some people say defines a planet, but it is by no means an established convention. And anyway, such a definition would leave us with hundreds, possibly thousands of planets in our Solar System, once the Oort Cloud and Kuiper Belt are accounted for, which is rather unworkable. As to your claim that a planet has to be solid, why do you assume that? Just because we can't land on Jupiter doesn't make it any less of a planet. [[157.140.6.143 11:06, 25 May 2005 (UTC)

text: He didn't write "has," and he didn't mean "as."  His native language doesn't seem to be English, and probably what he meant was that "he'd sooner consider Pluto as a planet than Jupiter."  That is, that Pluto was definitely a planet but that Jupiter, one of the original seven planets which the word was coined to describe, might not be.  This, like much of the author's contributions, is not helpful. 24.22.58.51 08:59, 26 November 2005 (UTC)
replies: text: I think that Pedro's point is that Pluto has a lot more in common with Earth then Jupiter does.  Only the lack of fusion prevents Jupiter from being a star, so what is the value of a definition that lumps Earth and Jupiter together, but excludes Pluto? The logical conclusion of Mike Brown's new position is that the word "Planet" might be unsalvageable.  Algr 06:55, 31 December 2005 (UTC)
thread_title: Pluto

message: This image portrays the Moon as much smaller than it actually is.  It should be edited or replaced.  Pluto is actually about 2/3 the size of the Moon, not 5/6; the Earth is about 3.6 times as big as the Moon, and the picture shows it at about 4 1/2 times as big.
:The image has now been retouched to reconcile the scales of the images.
:Urhixidur 20:08, 21 December 2005 (UTC)
replies: text: Hi there; thanks!  I uploaded the prior image, with the major bodies indicated in the article (adding and resizing based on averages), but assuming that the Moon was correct; my apologies!  The Moon looks larger than it should be (IMHO?), but I see the calculation that was used and take it as OK; I only suggest a mild realignment to make things ... neater. :)  Thanks again! E Pluribus Anthony 03:41, 22 December 2005 (UTC)
thread_title: "Relative Sizes" Image

message: The problem with "planet" boils down to one's emotional investment in the term. In times long past, there were the Seven Planets. Nowadays its just another word for a class of celestial object. Arbitrariness is unavoidable, like the minimum size cutoff of 50 m for asteroids. Urhixidur 12:57, 2005 May 26 (UTC)
:I don't understand the argument that having hundreds or thousands of planets in our solar system would be unworkable. Astronomers would keep track of them anyway, regardless of whether they are defined as planets or not, so there is no extra work. In fact I think the statement "To refer to them both as planets and as members of their own distinct populations would make the word "planet" essentially useless in practice." should be removed from the article, since it's meer opinion. Horatio 08:02, 30 July 2005 (UTC)
replies: text: The problem as I see it is that these populations have their own separate geological and astronomical histories. Ceres arguably has more in common with another asteroid in its belt, regardless of whether that asteroid is spherical or not, than it has with Pluto, Jupiter or Earth, just as Pluto has more in common with other trans-Neptunian objects then it has with Ceres. Therefore, to claim that, for instance, all Kuiper belt objects are part of a distinct population, except a certain number that are also planets, or that all main belt asteroids are part of a common population, except the ones that are also planets, creates unneccessary confusion (not necessarily for astronomers, but for kids in school who have to learn them) and gives the impression that sphericity is a more important shared attribute than composition, origin or location.  Serendipodous 18:31, 7 September 2005 (UTC)

text: Sphericity in this context is only considered important because it's a physical change that occurs when an object reaches a certain size, so can form a convenient definition for "planet". Whether an object is a planet or not by this definition would in no way change its independent attributes, such as whether it's a member of a belt. For kids, I think it's always going to be easier to explain a simple rule than to expect them to understand a rule with all kinds of arbitrary exceptions, or worse, an arbitrary list of objects that needs to be memorised. Horatio 09:27, 30 July 2005 (UTC)
replies: text: Perhaps. But that definition of planet is a bit like saying that a whole orange should be classified differently from an orange that has been cut into wedges. Serendipodous 18:31, 7 September 2005 (UTC)

text: It may be that the word "planet" now has too much history, and describes both the nature of an object and the orbit that it's currently in, with a definition that has been patched up several times for new discoveries. I think it would be nice to have a word to describe a spherical object with a solid surface, regardless of its orbit or lack of orbit, although "planet" is most likely not the most appropriate Horatio 10:07, 30 July 2005 (UTC)
replies: text: Well, it took about 20 revisions but I finally found a phrase to end that paragraph that I am happy with. Personally I don't think the word "planet" has been patched up at all. It's lagging behind the observations and, really, should either be ditched or limited in such a a way that it is at least consistent. Serendipodous 18:31, 7 September 2005 (UTC)

text: This revision is an improvement. However I'm not convinced that there's no need for generic terms. Otherwise you end up with terms like "Trans-Neptunian object", resorting to the word "object" which is so vague as to be almost meaningless. Horatio 12:29, 30 July 2005 (UTC)
replies: text: I have no problems with generic terms, only generic terms that are misleading or inaccurate. Any definition of planet that includes members of distinct populations should include every single one of those population members. To create an artificial distinction between members of a population based on shape is to give far too much importance to an inconsequential attribute. It is akin to creating separate species of human based on race. Serendipodous 18:31, 7 September 2005 (UTC)

text: I don't agree, because by this principle you can't have any categories of objects at all. There's no reason why this rule for planets shouldn't then be applied to other sorts of objects. If a certain cloud happened to contain stars, "planets", rocks, and dust, then you could no longer define any of these terms because they wouldn't include all members of that population.  Horatio 11:23, 31 July 2005 (UTC)
replies: text: Yes, Pluto had a different formation, like Jupiter had from Earth's. That's why there are the rocky planets, the gas planets /giants and the ice planets. We only had until recently one ice planet, now we have at least two. Other planetoids should have the name "planet" but they should be renamed after Roman dieties, asteroids smaller than 10 km should not be named but numbered, asteroids bigger than 360km should be renamed at least as planetoids, IMO. -Pedro 10:09, 3 August 2005 (UTC)
replies: text: Seredipitous here. Sorry for not being logged in; I am not on my computer. Pedro, you misunderstood the point I  made in that paragraph. Of course gas giants are more similar to one another than they are to the terrestrial planets. But there are no objects in the solar system with the exact same composition and origin as gas giants that we do NOT call gas giants. The term gas giant is universally applied to all members of the group, and there is no arbitrariness. With the Kuiper and asteroid belts, the situation is different. Some Kuiper belt objects are round, some are not; one asteroid is round, the others are not. Yet they all have similar compositions, origins and orbits. Why claim that some parts of the Kuiper Belt are intrinsically different from others, simply because they are round?
***answer to Seredipitous: Well, but there are terrestial asteroids, some are planets and some are asteroids.... the same occurs today with the KBO's some are planets some are asteroids. That paragrah is not very neutral and it is missleading (one thinks Pluto is an asteroid, although it is a planet). changing your question, for you to andswer: "Why claming that some parts of the "Terrestial" Belt are instrinsically different from others, simply because they are round? " There are many asteroids near the Earth and many intercept Earth orbit. So, you doubt Earth is a planet because it is round. For you what's a planet??? -Pedro 20:29, 10 August 2005 (UTC)
replies: text:  I believe that is the question that this article is meant to be asking :-). I did not write the concluding paragraph to this article but I agree with it; there is no one definition that anyone could create that adequately describes what is out there. My feeling is that, as our knowledge of extra-solar planets increases, we might find that there really is no difference between *gas giant* and *brown dwarf*, or between *terrestrial planet* and *moon*. It may be that the term *planet* will eventually die (it was, after all, coined three thousand years ago to describe a completely different cosmology) and be replaced by a series of terms that better describes the astronomical reality. But that is only a guess.Serendipodous 18:31, 7 September 2005 (UTC)
thread_title: Arbitrariness is unavoidable

message: The definition has changed over time. It has sometimes been an extensional definition (a list) and sometimes an intensional definition (the necessary and sufficient conditions for belonging to the set) at various points in time, and still is for many non-scientists. Today in scientific use precising definitions are used which fine tune the dictionary definition (lexical definition) of the term for the specific issue under discussion.
# maybe deleting the first "lexical" would help no-name's problem.
# changing "initially" and "becoming" as it did go back and forth as you say (since this is the intro, I was trying to simplify things)
# finally being clearer that EACH differnet use can get a different precising definition.
Better? Any futher enhancements needed? Or does this just make it worse for you? (I prefer the [first A then B then C] even if it is a gross simplification.) WAS 4.250 16:41, 31 July 2005 (UTC)
replies: text: That example is fine. Believe it or not, I am not trying to antagonise you about this. The brusque tone of my initial post was largely in response to being referred to as a vandal. I honestly just want to make sure this article is correct. As an aside, my apologies for not having an account name but, for some reason, my old name isn't recognised here anymore and I can't start up a new account without creating a dummy e-mail address to go with it, which is too much hassle for one username. Serendipodous 18:33, 7 September 2005 (UTC)
replies: text: You CAN start up a new account. The e-mail field is optional. For example, I left that field blank on THIS account. WAS 4.250 13:10, 1 August 2005 (UTC)
thread_title: What might be better

message: ::Could I just ask you a few questions to clear up some fuzziness? First, what would happen if an object only slightly less massive than Mercury were discovered? Also, can Venus, Mars and Mercury be said to have magnetic fields, when they wouldn't have magnetic fields were it not for the interaction of their atmospheres with the solar wind? Or have I misinterpreted what I read?Serendipodous 18:34, 7 September 2005 (UTC)
replies: text: Thanks for the info! (as you can see, I am now named)
Serendipodous 18:34, 7 September 2005 (UTC)
thread_title:  Magnetic Fields and Mercury 

message: What about a moon controversy. How can space rocks around planets be classified as moons. Shouldn't we have two types of moons? maybe moons (or secundary planets or even satellite planet) for Titan, Ganymede, Europa, our Moon and another notable moons (honestely I find moons more interresting than main planets), maybe "natural satellites" for those smaller objects (or another name for these space rocks). today all terms are applied to all objects. If we only would name bigger objects with Roman dieties, we wouldnt have today's problem with so many freaky names that no one can remember. --Pedro 10:01, 3 August 2005 (UTC)
thread_title: definition of a moon

message: I'm a bit confused by these two terms; one, I think, refers to a single, definable region of the solar system, while the other could refer to everything up to the Oort Cloud. I'm going to try and draft a section for the article that makes a distinction between these two terms.Serendipitous 10:32, 8 August 2005 (UTC)
replies: text: Don't edit about that if you don't know what it is. And I doubt that relation you made is truthfull. --Pedro 10:18, 8 August 2005 (UTC)

text: From what I've recently read: Kuiper Belt Object (KBO) is not a correct name for these objects, because someone prior to Kuiper has theorized about these objects, so Trans-Neptunian Object (TNO) is a more neutral name. If TNO includes or not the Oort Cloud I don't know. Even after reading that article. Use more than one source to validade something. -Pedro 11:11, 8 August 2005 (UTC)
replies: text:  Given the distance of the Oort and the smallness of the objects within, this question has never arisen, even in astronomy, as no Oort cloud objects have been identified. "TNO" refers to all objects in the solar system with their orbits at least partially outside the orbit of Neptune, but so far all of those objects have also been KBOs and a few SDOs. Because of this, there probably aren't many sources to set a precedent on this matter. siafu 14:25, 8 August 2005 (UTC)
replies: text:  You're forgetting about 90377 Sedna, which is considered to be an "inner Oort cloud" object. --EMS | Talk 15:36, 8 August 2005 (UTC)

text:  Considered by some.  It's hardly universally accepted as part of the Oort. See . Regardless, the point still stands: it's not clear whether "TNO" indicates Oort cloud objects or not because there hasn't been much reason to decide.siafu 15:46, 8 August 2005 (UTC)
replies: text: Found this table at Plutino, which ought to clarify the hierarchical classification that Serendipitous was originally asking about. --Eric Forste (Talk) 02:26, 10 August 2005 (UTC)
replies: text: Most excellent. siafu 04:48, 10 August 2005 (UTC)
thread_title: Kuiper Belt vs. Trans-Neptunian region

message: *look: http://www.space.com/scienceastronomy/060125_smallest_planet.html a rocky planet 5,5 times bigger than Earth. Maybe they would see Earth as an asteroid. The planets that are being discovered outthere are way bigger than Earth. And maybe, the Plutonians (inhabitants of Pluto) think: 
hey what are those four rocky balls after Jupiter - We know Mars since 1930s - but we now discovered an object bigger than Mars, the Earth! these are Trans-Jupiter (Belt) Objects, the TJO's! There are four large (we have also discovered more recently, one also the size of Earth (Venus) and one even tinier (Mercury), and also a medium sized (ceres) and several other tiny rocks in a very caotic belt known as Anti-kuiper Belt. Because they are so many and that space is full or rocks, Mars will no longer be considered a planet. these four (or five) planets should be removed from Planethood. And Earth is just a big asteroid!---Pedro 21:10, 25 January 2006 (UTC)
thread_title: Asteroid Earth

message: Please, be careful how you edit a Wikipedia page; be sure to read the whole article before you make an addition. Much of the information you posted was already mentioned and discussed in the article, in different sections; in particular, the links you posted were almost all already listed in the "External links" section at the bottom. On that subject, please stop posting massive external links in the middle of pages. If you want to post an external link, post it in the "external links" section, or indicate it with a number. Links do not have to have the full web address on the page- all you have to do is click the "Link" icon on the top of the page, and you can write a link like this: link title. Make the link title a simple number, and save a lot of room. Plus, I am assuming that English is not your first language, as much of what you wrote was grammatically confusing. It would help if you made clear what you intended to write on the discussion page before you posted it.Serendipitous 19:23, 28 August 2005 (UTC)
replies: text: If you don't specify anything, it gets numbered automatically.  This is the best way to do it.  , , etc. siafu 12:52, 29 August 2005 (UTC)
replies: text: WTF is the point in a linking style that adds meaningless numbers that are unsuitable to reference because they will change whenever a new link is added and what if anything is the policy document that supports using this fucked up style? Plugwash 13:53, 22 September 2005 (UTC)

text: It is not usual Wikipedia style to add explicitly-numbered anonymous links into articles.  If you want to add references, see Template talk:Ref.  Also, the implicitly-numbered links are deprecated according to the Wikipedia Manual of Style.  There's usually a better way to include links in an article.  --Doradus 16:27, 9 November 2005 (UTC)
thread_title: Yisraelasper

message: In the article, it states that the cutoff for "planethood" should be "when an object becomes spherical under its own gravity".  Later in that section, as well as on this discussion page, it has been stated that this criterion "conveys only that they are round".  It also says in the article that "it would not only let Pluto into the planetary club, but also Ceres".  If one reads the wording carefully, one sees that this is not what the criterion means.  While this criterion would mean that all planets are round, it does not mean that all round objects orbiting stars would be considered planets.  The phrase "under its own gravity" is the key point.  This criterion therefore convey's more about mass than about shape.  I'm sure there are many asteroids in the asteroid belt that just happen to be round.  That does not mean that they are that way because of their own gravity.  A baseball is round, but it is so because it was made that way, not because of the baseball's gravity.  My point is that Ceres would not necessarily be deemed a planet by this criteron (I don't know if Ceres is actually big enough to be spherical _due to its own gravity_.. someone please clarify this point).
As an additional note, this criterion might actually say something about composition, since some bodies may require less gravity to become spherical than others depending on composition, though I do not have the expertise to know if this would be the case.  I am only pointing out a flaw in the article's reasoning.
: I think that you should be careful here, because this article is reporting the logic of others.  You are right that composition will play a role, since denser substances will tend to create stronger gravitational fields, and at the same time the ability of the substance to handle a mechanical load is also an issue.  However, these are interesting details.  As a practical rule of thumb that does not require you to wiegh or measure the size of an obect, this definition workds quite well.  As a practical matter, the smaller an object is, the less likely it is to be round to begin with.
: As for Ceres, it is round due to its gravity.  Many somewhat smaller moons also are also round in the same way.  However, no other asteroid meets the criteria.  Even the second biggest asteriod, Pallas in non-spheroidal, with its dimensions being 570×525×500. --EMS | Talk 02:59, 25 September 2005 (UTC)
replies: text: The section objecting to the "sphericity" argument is the most unfair, POV and unsubstantiated part of this article. Since I wrote it, I know what I'm talking about. :) I have long wished for someone to redraft it (not me obviously, since I cannot overcome my pathological hatred of the "let's randomly select objects for planethood based on their shape" bandwagon) but so far no one has done so (at least not without completely misinterpreting it). In an attempt to find an unbiased answer to all of these questions, I posted this very question to an astronomy board, but if anything, their answers made the issue more confusing, not less: See here, I honestly don't know what to do at this point. Serendipodous 15:12, 25 September 2005 (UTC)
replies: text: *in fact the roundness is the best physical argument for planethood, there are just some people that don't accept more than 9 planets. 21st century: Dark ages for Astronomy naming and conventions, IMO. Ceres was classified as an asteroid, because the telescopes of the time werent good enough. And Ceres is a singularity among the asteroids. -Pedro 22:34, 26 September 2005 (UTC)
replies: text:  I have no problem with more than nine planets; I just have a problem with some objects being planets while other objects that are otherwise identical to them apart from being slightly smaller not being planets.Serendipodous 07:20, 27 September 2005 (UTC)

text: * Personally I think that you do an excellent job of covering that issue.  I see what you mean about there being some POV in it, but it is not as if the scientific community is running to embrace this definition.  I think that the point of that section is very, very good:  no matter what you do, there will be some object that does not quite fit the definition well.  Even for roundness cutoff, there is a transition zome such that on either side of it you can say this "is" or "is not" a planet.  However, in between there will some arbitrary standard such that if an object is just a little bigger or a little smaller od a little denser its status suddenly changes.  There is not much that we can do about that. --EMS | Talk 22:54, 26 September 2005 (UTC)
replies: text: *The main objection to the roundness cut-off is that it's not exact. It varies based on composition and heating conditions. Mimas is the smallest known near-sphereical object in the solar system. 2 Pallas is slightly larger and much more massive, but is distinctly non-spherical. 4 Vesta is slightly more massive than Pallas, but has a more round shape, possibly indicating partial gravitational relaxation into a sphere. Both asteroids contain a much higher percentage of rock than Mimas, which is mostly water ice. Enceladus and Miranda are also spherical and smaller than both asteroids. Proteus is more massive than Mimas and composed of similar substances, but is non-spherical, probably because it's further from the sun. Further, some objects have a shape that isn't gravitationally relaxed, but balances gravity against the forces of the object's rotation. Jupiter has an oblate shape because of this, and in a more extreme example 2003 EL61, which has a 4-hour day, is streched into the shape of a rugby ball. Some objects, like Mimas, are distorted because of tidal forces. Most of this information is scattered about inside the article. Maybe we should add a table illustrating the size of sperical and non-spherical bodies, showing the fuzzy nature of that boundary? shaggy 20:36, 21 January 2006 (UTC)
replies: text: *I think that's a good idea; do you know how to construct a table? I don't really know how. Would appreciate the help. By the way, this section dealt with an earlier version of this article that was a lot more POV than the current one. Serendipodous 09:46, 22 January 2006 (UTC)
replies: text: * See Wikipedia:table for help.  However, I scratch me head about this a bit.  Enceladus is a moon and is also liquid on the inside.  I find it inappropriate to compare an oversized water droplet to an ice/rock object which is circularized due to gravity itself. --EMS | Talk 05:34, 23 January 2006 (UTC)
thread_title: Clarification on "Roundness" Cutoff

message: Some external links were sprinkled randomly into the article recently.  I have collected them into a proper References section, but I'm not sure they really add anything to the article in the first place.  Opinions?  --Doradus 14:29, 25 September 2005 (UTC)
thread_title: New References section

message: What if only smaller bodies can have more than one spin axis. Would that not set a natural size limit to use in defining a planet?Jan Pedersen 11:02, 27 September 2005 (UTC)
thread_title:  Spin axis 

message: I think reclassify is better, there is no ranking of heavenly bodies.--Perfection 06:28, 4 October 2005 (UTC)
thread_title: The Term Demote

message: There seems to be a slight contradiction in the sentance newly added by Tompw:
"The required distance depends solely on the mass of the planet. (The further the planet is from the Sun, the further the moon needs to be from the planet)."
If the planet's distance from the Sun is a factor in the required distance, then it can't solely be related to the mass of the planet.Serendipodous 17:38, 4 November 2005 (UTC)
thread_title: Query about recent addition

message: in the history page. You seem to be suggesting Herschel fudged his results; I fail to see how he could have had an accurate measure of Ceres' and Vesta's sizes, given the accuracy of telescopes at the time. Also, size isn't really the point of that section; the issue is a shared orbit. Size is covered in the following section. Serendipodous 23:25, 28 January 2006 (UTC)
thread_title: Pedro, I'm a bit confused by your comments on Herschel

message: Substituted at 20:23, 2 May 2016 (UTC)
thread_title: Assessment comment