Talk:Dwarf planet/Archive 2

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Archive 1 Archive 2 Archive 3

Interesting dwarf planet candidate list

I thought some editors might find this interesting. They figure that 2002 UX25 is not a candidate, and that 1996 TL66 and Huya are. Of course, most of their candidates are up in the air, but just thought it was worth bringing up here. --Patteroast 00:01, 10 July 2007 (UTC)

Are these in our solar system?

This page doesn't make it clear if dwarf planets have only been discovered in our solar system, or if they've been discovered in other solar systems, too. It would be nice if someone could fix this so it's more clear. Thanks, Fredsmith2 20:13, 7 October 2007 (UTC)

Currently, the ability to discover dwarf planets outside of our solar system is beyond our abilities (other than possibly through a very lucky transit event). So, the question remains though (and I don't know the answer to this) does the definition of dwarf planet necessitate that the object be in our solar system (as the lede suggests)? Clearly, the definition as put forth by the IAU suggests this is the case ("is in orbit around the Sun"), but the definition of planet has the same wording, so I'm not sure what's appropriate here. Ben Hocking (talk|contribs) 20:36, 7 October 2007 (UTC)
I think what the resolutions mean is that the IAU has adopted actual definitions only for objects orbiting our Sun. If you look at the IAU document that is referenced in the article Extrasolar planets, you will see that they are far less precise regarding objects orbiting other stars. They use terms like "planetary companion" and mention that some of these objects may be "brown dwarfs" or other types of objects. It makes sense not to classify these objects, since we humans are really still at the very beginning of discovering them and figuring out what they are, and in most cases we haven't even "seen" them. The history of planetary discovery in our own Solar system suggests that caution is the correct approach; when Ceres, Pluto and other objects were first discovered, they were immediately classified as "planets", then eventually, as new objects were discovered, the astronomers figured out that this approach was not working. There's no rush in defining these things, we've got the rest of eternity. 6SJ7 01:31, 8 October 2007 (UTC)
Makes sense. Could someone who knows how to word it, please reword the first paragraph so that it reads that these are in our solar system? I'm a surgeon, not a bricklayer or an astronaut. Fredsmith2 00:45, 9 October 2007 (UTC)
It's already in the first sentence. Ben Hocking (talk|contribs) 01:20, 9 October 2007 (UTC)
Actually it's not beyond our abilities. The condition is, it has to orbit a pulsar. And yes, the IAU definition requires it to be in the Solar System, and so the planet. There is a draft resolution (2003) for the definition of planet outside the Solar System. (talk) 23:14, 22 November 2007 (UTC)


I did a quick search to get diameter estimates. I left something of a mess, with multiple estimates, some of which are probably dated, in the hopes that someone who knows the reliability of the data would be able to clean it up a bit. kwami 14:28, 7 November 2007 (UTC)


The article has been nominated for Wikipedia:Article Collaboration and Improvement Drive.Nergaal (talk) 20:17, 20 November 2007 (UTC)

One of the things to clean up is the sortable table. The sorting doesn't work with exponentials. kwami (talk) 21:01, 20 November 2007 (UTC)

Somebody should check this link and update the article —Preceding unsigned comment added by Nergaal (talkcontribs) 17:35, 6 September 2007 (UTC)

Not a Satellite?

What does the IAU mean by "is not a satellite" in its definition of dwarf planet? This seems to directly contradict the first clause of the definition stating that it "is in orbit around the Sun."[[1]] By the standard definition of satellite, "a celestial body orbiting another of larger size," a dwarf planet orbiting the sun should indeed be considered a satellite.[[2]]
Cgnu 08:40, 6 May 2007 (UTC)

I noticed this too. The IAU website only lists the first three conditions. The fourth condition is mentioned on the NASA website but not on IAU. Can someone with more knowledge in the field enlighten us? My understaning is that satellites are in orbit around the sun (as well as a planet) and therefore the fourth condition is necessary to exclude the satellites from the definition of dwarf planets. Alex.g 22:36, 10 December 2007 (UTC) —Preceding unsigned comment added by Alex.g (talkcontribs)

"Dwarf" is the wrong term for what the IAU had in mind

The use of "dwarf" in this context is an adjective so a "Dwarf Planet" is still a Planet and not a separate classification of solar system objects.

This leads to the conclusion that all of the so called "Dwarf Planets" really are extra planets above the traditional 9 we all used to know about before this change in classification. —Preceding unsigned comment added by (talk) 18:39, 26 November 2007 (UTC)

You are interpreting "dwarf planet" in an English context. "dwarf planet" is a single term, without an adjective. Sure, if astronomers were English majors, they might have though of doing it a different way... but they're not. (talk) 22:40, 26 November 2007 (UTC)
Just the same in any other language. For example Russian "karlikovaya planeta", a direct translation of "dwarf planet" reads even more ugly than Eglish one (because it's too long in my mind) and can be interpreted as "very small planet". This is confusing both because dwarf planets are not too small (if to compare with minor planets for example) and are not planets at all in the current classification.--Dojarca (talk) 20:46, 28 November 2007 (UTC)
I agree though (with the section title) that the word 'dwarf' is a poor choice. But then, there are lots of poor wording choices that have become idiomatic in English. kwami (talk) 23:09, 28 November 2007 (UTC)
Isn't the use of dwarf in the English version kind of... offensive in regards to the perception of "dwarves" culturally? I know that calling a little person dwarf or midget is considered pejorative, for instance. —Preceding unsigned comment added by (talk) 03:36, 2 December 2007 (UTC)
"dwarf" is very common in astronomy. white dwarf star, dwarf galaxy, red dwarf star... The Sun is a yellow dwarf. There's also a term called "degenerate dwarf" (talk) 23:17, 6 December 2007 (UTC)

The word Dwarf Planet

The word Dwarf Planet is properly only for our solar system but it has gotten a looser usage too just like many words

Hello I realize that properly a Dwarf Planet is an object in the solar system. I was surprised and dismayed when I first learned that to a lesser degree it is being used for outside our solar system. That it has such a usage is all that is being pointed out by me. Yisraelasper (talk) —Preceding unsigned comment added by (talk) 10:58, 1 January 2008 (UTC)

Preparing for GA/FA

I have worked on the article quite a bit. I need to add citations to where I allready placed the tags myself (i.e. the text is good but references are required for GA). If you have tips you are welcome to leave them here, or if you want to contrigute with references you are welcome too. Nergaal (talk) 10:40, 26 January 2008 (UTC)

I am done with the article. You are welcome to wikify it. Once the review is done, I am going to nominate it for GA/FA.Nergaal (talk) 13:52, 26 January 2008 (UTC)

merge section?

The "largest objects" section of Trans-Neptunian object duplicates the "candidate objects" section of this article. Since the physical parameters of these bodies are so uncertain, and there are so many estimates floating around, I think we should merge here to keep our account and references consistent. kwami (talk) 23:52, 26 January 2008 (UTC)

Sounds ok. There is also the option of transforming the table into a template; this could mean that it might be harder to edit the values (a good thing against vandalizations?).Nergaal (talk) 00:33, 27 January 2008 (UTC)
I think a template would be better. kwami (talk) 02:34, 27 January 2008 (UTC)

Successful good article nomination

I am glad to report that this article nomination for good article status has been promoted. This is how the article, as of January 28, 2008, compares against the six good article criteria:

1. Well written?: Pass. The article is very easy-to-follow and user-friendly, while still offering technical data
2. Factually accurate?: Pass. The inclusion of citations is very good, although a few sections still require citation
possible citation [3]Nergaal (talk) 03:16, 28 January 2008 (UTC)
3. Broad in coverage?: Pass. The article properly addresses the topic in all respects
4. Neutral point of view?: Pass. The discussion of the controversy was written with a very neutral POV.
5. Article stability? Pass. Although the article has undergone SIGNIFICANT changes recently, it is a new article and this is understandable. As the article is largely complete now, I expect it will stabilize.
6. Images?: Pass. Some articles simply can't have that many photos, and this topic is one of them. The few present photos accurately provide the necessary information, so there is no reason to fail this section.

If you feel that this review is in error, feel free to take it to Good article reassessment. Thank you to all of the editors who worked hard to bring it to this status, and congratulations.— Codharris (talk) 00:43, 28 January 2008 (UTC)


Anyone got any final suggestions before a FAC? Nergaal (talk) 11:41, 29 January 2008 (UTC)


Hi Nergaal.
In the lead: "it is suspected that more than 70 other objects in the Solar System might belong in this category" and
"there are estimates that the number might increase to 200 when the region known as Kuiper belt will be fully explored, and might be around 2000 when also objects outside this region will be accounted for"
These claims should be clarified. Indeed, what kind of numbers are we talking about? We first estimate 70 more dwarf planets in the Solar System but then correct this estimate? This seems contradictory unless the first claim is tweaked to something like: Ignoring the Kuiper belt and other regions of the Solar System, it is suspected that more than 70 other objects in the Solar System might belong in this category. Randomblue (talk) 11:20, 10 February 2008 (UTC)

How is it now? Nergaal (talk) 08:16, 11 February 2008 (UTC)

disambig planetoid

Randomblue (talk) 15:12, 15 February 2008 (UTC)

why? it is just that the linked article is a stub.Nergaal (talk) 15:59, 15 February 2008 (UTC)

Map request

A plot of the orbits of the known dwarf planets would be helpful. -- Beland (talk) 08:44, 2 January 2008 (UTC)


I belive that Pluto... STILL IS FREAKING A PLANET!! —Preceding unsigned comment added by (talk) 21:36, 21 February 2008 (UTC)

Pluto was declared a Dwarf planet during 2006. I guess it depends on what you mean by planet. Planets are planets, but the mid-sized dwarf planets and the smaller minor planets (AKA asteroids) are not planets by the current definition, even though they have "planet" in their name. Confused yet?
When Pluto was first discovered, it was thought to be larger than Mars and was thus categorized as a planet...but it turned out to be an icy body (high albedo) and thus was much smaller than the other planets, although still much larger than the asteroids. Then the Kuiper belt (sort of an asteroid/comet belt at the edge of the solar system) was discovered, and Pluto was labeled a Kuiper Belt Object. Still a planet? Then Eris (AKA Xena) was discovered, and suddenly there were ten planets...or perhaps eight.
If Pluto was as large as was originally thought, it would definitely be a planet. As it is, it's smaller than the other planets and much bigger than non-spherical asteroids (AKA the "minor planets." The debate on Pluto's status has been raging for some time. Twenty years ago, Isaac Asimov suggested the category of mesoplanet for objects bigger than Ceres and smaller than Mercury, which at the time would have put Pluto in its own category. With all these KBOs being discovered, however, it's likely that the register of dwarf planets will continue to grow. Arch O. La Grigory Deepdelver 18:05, 27 February 2008 (UTC)
I agree, Pluto is still a planet. Why is Wikipedia still using the discredited IAU definition of planet? There are other Astronomical organizations out there with different definition of Planet. Use a organization that is creditable. Not one that waited until only 400 people were left before taking a vote. Thats my opinion on the matter. Magnum Serpentine (talk) 14:28, 23 May 2008 (UTC)
As regards to definitions used in Wikipedia, if it after some years, happenstance occurs that humans cannot use the IAU definition because of it's linguistic flaws, we should consider disusing the IAU definition, but that will take a while, and personally I consider Pluto and Ceres being nice "sub-planets" - thingies that share some planet qualities but are too small to really be regarded as planets. "Sub" usually means "too small", "under" and "below". Said: Rursus 20:44, 15 July 2008 (UTC)

This is not the place to discuss whether or no Pluto is a planet. If you have information relating to the IAU being discredited or other large astronomical organizations that use a different definition of planet, make the edits and cite your sources. Remember that Wikipedia is not a forum.shaggy (talk) 00:03, 18 July 2008 (UTC)

Maybe, but the topic here is whether it is freaking a planet, and now we discuss terminology to be used. Rursus dixit. (mbork3!) 16:42, 28 January 2010 (UTC)

Broken reference

Perhaps someone who can edit this page could update the broken reference to "The IAU draft definition of 'planet' and 'plutons'". The new location seems to be

Thanks! —Preceding unsigned comment added by (talk) 19:49, 16 May 2008 (UTC)

I added new link. Ruslik (talk) 08:46, 17 May 2008 (UTC)


Looks like "dwarf planet" has been replaced with "plutoid" for objects beyond Neptune.

What verification is needed before making the appropriate changes to this article? Daveharr (talk) 15:30, 11 June 2008 (UTC)

I think it hasn't, I think the taxo tree is:
  • "Dwarf Planet" - a not-cleared-the-neighborhood "sub-planet",
    • Plutoid - a not-cleared-the-neighborhood "sub-planet" in the "outer solar system"
    • the rest - Ceres.
Said: Rursus 20:29, 15 July 2008 (UTC)
(A dwarf elephant is a non-elephant that hasn't cleared his neighborhood, such as Joe, Jim and Bill) Said: Rursus 20:31, 15 July 2008 (UTC)
Sorry, again: I think it hasn't, I think the taxo tree is:
  • "Dwarf Planet" - a not-cleared-the-neighborhood roundish non-planet which is not a star,
    • Plutoid - a not-cleared-the-neighborhood roundish non-planet which is not a star, and that is in the "outer solar system"
    • the rest - Ceres.
Said: Rursus 20:34, 15 July 2008 (UTC)
Sorry, again: replace "star" with "fusor"! A "fusor" is a star or a Brown Dwarf. Said: Rursus 20:39, 15 July 2008 (UTC)


Is it not true that Neptune shares its orbit with Pluto in some fashion? If Pluto is a KBO and a dwarf planet, would not that mean that Neptune, which crosses Pluto's orbit, has not cleared its neighborhood of KBOs? Should not then Neptune be considered a dwarf planet? I have 2 points here: 1, There is no upper limit on the size or mass of dwarf planets. 2, Neptune, by virtue of Pluto and other KBOs in the vicinity, has not cleared its neighborhood. Therefore, Neptune is a dwarf planet.

It seems to me that the definition of "Dwarf Planet" was tailored specifically to stop debates about Pluto and other "Dwarf Planets" but they failed to try to apply the definition to the other planets to see if they would be reclassified as well.

If the IAU's word is authority (there are not authorities in science), then I say that Neptune is infact a dwarf planet. If the Trojan Asteroids were not in Jupiter's Lagrange Points, I would venture so far as to declare it a dwarf planet as well. But even then, this means that Neptune, having not cleared its vicinity of smaller objects and even failing to clear it of planetesimals such as Pluto, is a dwarf planet. Meanwhile, Earth, having even gone so far as to absorb a Mars sized planet (or as commonly theorized for the creation of the moon), is a Super Planet. Doesn't this seem a little disproportionate?

In closing, I declare the IAU about as schizophrenic as any committee can possibly get. 9,664 voices in the IAU's head, apparently it's too noisy to actually come up with anything that actually makes sense. (talk) 16:25, 11 June 2008 (UTC)

Actually, Neptune has cleared the neighborhood. Pluto is in a resonant orbit, which means it is dominated by Neptune. Read cleared the neighborhood for the practical meaning of the phrase. kwami (talk) 18:54, 11 June 2008 (UTC)
As far as I'm concerned, Pluto's orbit is too close to Neptune's orbit to let Neptune off the hook. Neptune hasn't cleared out Pluto or any of the other stuff that Pluto hasn't cleared out. It's a dwarf planet, ironic considering it's probably also a super planet. As for the "orbital resonance" nonsense. That's explicitly defining an arbitrary exception. I'm sorry, but REAL scientists have no room for needless use of arbitrary definitions. The only time science needs to get arbitrary is when dealing with a purely arbitrary subject, not making excuses for definitions. Such as defining a planet's meridian. But even then, the equator would still be defined on a non-arbitrary piece of data. I reject the definition of "dwarf planet" and "plutoid" because of its silliness. Neptune is a dwarf planet, but not a plutoid, as Neptune cannot be beyond Neptune. And if the IAU had it's way, there are no extra solar planets, just a bunch of silly people measuring star wobbles. If we brought Richard Feynman back to life, he likely wouldn't even be interested in the IAU's recent incoherent babbling. That's because zombies are attracted to brains, and the IAU has very little of that it seems. In closing, I am also not adding "plutoid" to the spell checking dictionary on FireFox as it's not even a valid scientific concept, let alone a real word. (talk) 17:28, 14 June 2008 (UTC)
You didn't bother to read the article, did you? kwami (talk) 17:58, 14 June 2008 (UTC)


Here are the numbers for the "Planetary discriminants" table for Makemake: mass 6.7e-4; Λ/ΛE 1.447e-9; µ 0.02. I used wiki's data on Makemake's mass. For µ, both the Pluto and Eris entries seem to assume the "other mass" is about 1.7e23kg, so that's what I used. —Preceding unsigned comment added by (talk) 14:59, 14 July 2008 (UTC)

Since this is a FA, I would prefer a reference for these numbers... :( Nergaal (talk) 15:43, 14 July 2008 (UTC)
I think the table is from some scientific paper published like 8 years ago. The authors are not going to deliver an updated version for us. It's not Forbidden Original Research to divide "2" by "4" and get "0.5". This isn't even a matter of unnecessary information in an extra paragraph, it's a big blank space in a table, the info should only be removed if it's wrong. (talk) 04:31, 21 July 2008 (UTC)
Hence the un-smiley in Nergaal's post... From my point of view, we should reference the Makemake data, and give a note in the cite saying which value we are using for the "other mass". Simple calculations are, of course, not original research. For example, see this section of the Wikiproject Physics guidelines. Bluap (talk) 04:56, 21 July 2008 (UTC)

Inconsistancy Concern

I've started a discussion at Talk:Ceres_(dwarf_planet)#Inconsistancy_Concern over problems relating to information consistancey between this and two other articles. Gnangarra 06:00, 15 July 2008 (UTC)

Incorrect parenthetical note

I can't edit the page so I'll mention that in the "Current members" section the parenthetical referenece to Neptune's discovery is wrong: Ceres was discovered 45 years before Neptune, not 16. —Preceding unsigned comment added by (talk) 13:24, 23 July 2008 (UTC)

Thank you for taking the time to note that. -- Kheider (talk) 14:23, 23 July 2008 (UTC)


According to the current text of the article, Stern recognizes dwarf planets as planets, & counts Pluto as the 9th planet. This appears to be inconsistent:

  • Pluto would not be the 9th planet from the sun; Neptune would
  • Pluto would not be the 9th planet in size; Eris would
  • Pluto would not be the 9th planet to be discovered; Neptune would

In what sense would Stern count Pluto as the 9th planet if dwarf planets count as planets? I tried following the link given in the ref note, but it seems irrelevant; perhaps changed since retrieval. Peter jackson (talk) 08:27, 31 July 2008 (UTC)

Stern recognizes Pluto as a planet. The problem disappears if we don't assume he recognizes Ceres as a planet just because people he doesn't agree with have classified Pluto and Ceres under one label. kwami (talk) 08:56, 31 July 2008 (UTC)
But that's not what the article says. It says he counts dwarf planets as planets. Peter jackson (talk) 08:12, 1 August 2008 (UTC)
Nowhere the article says that he counts all dwarf planets as planets. Ruslik (talk) 11:12, 6 August 2008 (UTC)
No, he doesn't recognize that 'dwarf planet' is a valid category distinct from 'planet'. Ceres is still an asteroid, and Pluto the 9th planet. I don't know if he considers Eris the 10th planet, but for him it doesn't affect the status of Pluto. kwami (talk) 08:22, 1 August 2008 (UTC)
Again, I repeat: that's not what the article says. It says he recognizes dwarf planets as planets. If you think that's wrong, change the article & supply a reference. If somebody thinks the article is right, could they supply a reference? If nobody can find a reference, the material should be deleted.
More generally, if you go back to the proceedings at the IAU Congress, you find there were only 2 proposals on the table:
  1. final official decision
    1. planets
    2. dwarf planets
    3. SSSBs
  2. committee recommendation
    1. classical planets
    2. dwarf planets
    3. SSSBs
The only difference is on the 1 word "classical". Virtually nobody voted against both proposals. Unless something's changed since then, it seems reasonable to assume that virtually all astronomers follow 1 of these. Peter jackson (talk) 10:14, 6 August 2008 (UTC)
I'm sorry, I just don't see anywhere in the article where it says Stern recognizes dwarf planets as planets, so I don't know how to answer this. kwami (talk) 16:49, 6 August 2008 (UTC)
"Thus, he and his team still refer to Pluto as the ninth planet, while accepting the characterization of dwarf planet for Ceres and Eris (dwarf planet in this case meaning just a small planet)." Doesn't the bracketed material clearly imply that? Peter jackson (talk) 17:25, 7 August 2008 (UTC)

History of the name

That's what the section's called, but it seems to be mainly about the history of the concept. It doesn't even mention that the name was proposed in the original committe recommendation. Peter jackson (talk) 10:27, 6 August 2008 (UTC)

move 2003 EL61 to 'dwarf planet'

2003 EL61 is a dwarf planet "for naming purposes". That's all Makemake is too, but we've moved that to Makemake (dwarf planet). I propose we do the same here: the only difference with 2003 EL61 is the dispute over who discovered it, which prevents it from going through the naming process. That has absolutely nothing to do with the nature of the object.

I placed a Move? tag on the article's talk page. kwami (talk) 06:48, 27 August 2008 (UTC)

Makemake was categorized as a dwarf planet officially; 2003 EL61 was not. We have to wait for the IAU. --Ckatzchatspy 07:27, 27 August 2008 (UTC)
But it is a dwarf planet according to the IAU definition of a dwarf planet. Effectively, then, the phrase is not a scientific term at all if the body cannot be demonstrated to have achieved h-equilibrium, but a bureaucratic one. Perhaps we should reword this article to make that clear? kwami (talk) 07:44, 27 August 2008 (UTC)
I prefer to wait until it receives a name. EL61_(dwarf_planet) is not a good title for the article. Ruslik (talk) 09:30, 27 August 2008 (UTC)
I agree with the idea of WAITING until it has a real name. The public will appreciate it more when it has a real name. License plate numbers do not go well with the public. Besides, as a minimum, we need an official IAU statement declaring it as a plutoid or dwarf planet. In twenty years few will remember "2003 UB313", "2005 FY9", or "2003 EL61" by their license plate names. I see no problem with it being the top candidate. -- Kheider (talk) 16:11, 27 August 2008 (UTC)
I think this is a case where the No Original Research rule comes in. We can't decide for ourselves whether something is a dwarf planet. Peter jackson (talk) 17:11, 27 August 2008 (UTC)
Haumea (2003 EL61) is now officially a dwarf planet: —Preceding unsigned comment added by (talk) 19:49, 17 September 2008 (UTC)


There are some references to spherical, near-spherical or spheroidal shape as a requirement for being classified as a planet. However eg Haumea is none of these, but ellipsoidal (triaxial, longest axis = 2x shortest), and according to the first paragraph the requirement is only to be rounded by its own gravity.-- (talk) 16:00, 18 September 2008 (UTC)

Yes, that's better wording. kwami (talk) 19:47, 18 September 2008 (UTC)

Link Error

Discusion of link error obviated by fix.
The following discussion has been closed. Please do not modify it.

The link for Reference item #50 is broken. The "/" at the end of the link needs to be removed. VirtualDave (talk) 05:15, 6 December 2008 (UTC)

I tried to fix it. It's in a template for the table. I edited and saved the template, and the diff shows in my contributions [4], but the same error still appears on the main page. Someone else will have to do it. -- Another Stickler (talk) 12:41, 6 December 2008 (UTC)
Links fine for me. Maybe you just needed to clear your cache. kwami (talk) 12:46, 6 December 2008 (UTC)
It works now for me now too, so it must have been the cache showing me the old version. I'm folding up this section. If anyone knows how to archive it, I think that will save some load time. -- Another Stickler (talk) 17:32, 7 December 2008 (UTC)

Pluto is smaller than the moon

This is probably the best reason for Pluto not to be a real planet anymore. People are always assuming that it is larger than it is. Pluto (radius 1195km) is physically smaller than the Earth's moon (radius 1738.1 km). That would give Pluto only 68.7% the diameter of the moon. -- Kheider (talk) 17:55, 31 December 2008 (UTC)

If the Moon were in its own orbit, it would almost certainly considered to be a planet. There are a number of moons in the solar system which would be planets if they were in their own orbit, so I don't think being smaller than the moon is relevant.--RLent (talk) 20:04, 31 December 2008 (UTC)
Actually I mainly posted the above statement because someone had incorrectly updated the Physical attributes of dwarf planets table using the radius of the moon compared to the diameter of Pluto, and came up with Pluto and Eris being larger than the moon. I see this common mistake all the time. Since Pluto was known as a planet everyone seems to subconsciously perceive it as larger (and thus more exciting?) than our moon. -- Kheider (talk) 20:17, 31 December 2008 (UTC)

Dead link

Reference [26] does not work.--Roentgenium111 (talk) 22:45, 2 February 2009 (UTC)

Fixed. ... said: Rursus (bork²) 15:19, 5 February 2009 (UTC)

presentation order

There are two presentation orders that make sense to me: physically, by orbital period, and historically, by date. Discovery date doesn't work very well, though: do we use the IAU email date, the observation date, the precovery date, the date s.o. realized how big the object was, etc. I think the date the object was classified as a DP works best. That's what we all remember, at least, when the official announcement was made by the IAU. However, that causes some problems with the first three, which maybe we can discuss here? Ceres was the first demoted planet, so in my mind it should be first on the list. The difference in announcement date between Ceres, Pluto, and Eris was at a time when the whole DP concept was being ironed out, and speaks more of politics than history IMO. So the most natural order to me is Ceres, Pluto, Eris, Haumea, and Makemake. kwami (talk) 10:39, 16 February 2009 (UTC)

M was announced before H. Peter jackson (talk) 10:58, 30 March 2009 (UTC)

Haumea's orbital period: 283 or 285.4 years?

This article gives Haumea an orbital period of 285.4 years, while the Haumea (dwarf planet) and Makemake (dwarf planet) articles give around 283 years. Which is correct? The Haumea article suggests that the 283 figure is more consistent with a 12 : 7 resonance between Haumea and Neptune, whose orbital period is 165 years. Glenn L (talk) 15:33, 29 March 2009 (UTC)

The orbital peroid of all bodies is dynamic and varies depeding on the Epoch (astronomy) used, ie 1950 vs 2000. JPL currently uses an epoch of 2009 and shows a peroid of 283 years. Buie and the Deep Ecliptic Survey (DES) use an epoch of 1955 show an orbital period of 285 years. Neither is wrong because they are using different dates. -- Kheider (talk) 17:06, 29 March 2009 (UTC)

Grammatical error in section: History of the concept

The following line refers to a plural subject but uses the singular artical "a". For correct grammar, please remove the "a".

"...started to be used for the bodies now known as a dwarf planets." —Preceding unsigned comment added by Mrbynum (talkcontribs) 17:29, 6 May 2009 (UTC)

Logically inconsistent definition

The very first sentence of this article presents a logically inconsistent definition of "dwarf planet". It states:

"A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of planetesimals and is not a satellite."

This definition includes these propositions: A - A dwarf planet orbits the Sun. B - A dwarf planet is not a sattelite.

Now, a satellite is an object in orbit around another object*. So the intersection of A and B is the empty set. Okay, fine, maybe it's not technically logically inconsistent, but it is vacuous. Then the article goes on to list some specific examples of dwarf planets, none of which satisfy the definition (of course since nothing could possibly satisfy the definition).

*Technically object A is a sattelite of object B if and only if the they orbit a center of gravity of the two object system that is located within the volume occupied by object B.

How do they not satisfy the definition?
Satellites orbit the Sun. They just do so while simultaneously orbiting another body. Maybe the IAU felt they had to spell this out for the overly literal.
That is not the technical definition of a satellite. It has been proposed, but AFAIK has never been adopted by the IAU. It causes problems because a distant object might not qualify as a satellite despite being small. For example, the center of mass of the Sun-Jupiter system lies outside the Sun, so if we took your technical definition as a general statement of one body orbiting another, Jupiter would not qualify as a planet, but instead would be one component of a failed double star system.
Hey, this is fun! Let's take your technical definition as a general definition of "orbit". Then we have seven planets, and Jupiter is presumably a failed star. Since the Galileans have cleared their orbits, they are planets, bringing the total to eleven. However, the IAU definition of a planet is that it orbits the Sun, but the IAU still speaks of extra-Solar planets, so the logical conclusion is that the Sol system consists of 11 planets: 7 Solar planets, and 4 extra-Solar planets.
Another problem with the IAU ruling is that planets are satellites by definition, since they orbit their primary, and that's all a satellite is.
(Lest anyone take me too seriously, I am not proposing that we make the claim that the Solar system has eleven planets.) kwami (talk) 06:29, 18 May 2009 (UTC)
Perhaps worse yet, using the barycenter definition, some satellites on an elliptical orbit could travel in and out of the "definition zone" with every orbit... There will never be a perfect definition of a planet. -- Kheider (talk) 13:34, 18 May 2009 (UTC)
Someone did point that out to them, & they changed the wording to say the majority of the time, or some such. Academic anyway, as the definition was never adopted. Peter jackson (talk) 17:38, 27 August 2009 (UTC)
The definition is simply incomplete. The word Sun is used when the more general term of "a star" would be more appropriate. The writers of the definition simply assumed that anyone would realize that. The IAU also assumed that it would be obvious that a satellite orbits another body that, in turn, orbits a star. If an object directly orbits a star it is a planet(or dwarf planet, or planetessimal, etc.) Khajidha (talk) 22:58, 23 October 2009 (UTC)
Yes, it's incomplete. It was intended to define only planets of our sun. Why, I don't know. The 2nd part of your remark is correct. Peter jackson (talk) 09:31, 24 October 2009 (UTC)
Honestly I think we shouldn't get too bogged down in the definition of a satellite and use a clearly stated explanation of our own that follows the *intent* of the IAU ruling but makes it clearer to the average user of Wikipedia. Something along the lines of "is a celestial body that primarily orbits a star rather than a planet, and is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of planetesimals." —Preceding unsigned comment added by (talk) 13:23, 1 January 2010 (UTC)

Since we're getting off base here in debating the science ( a good thing) rather than critiquing the article (which can also be a good thing) let me add: astonomically a satellite is understood to be a natural object that orbits a planet. The term is synonymous for moon, which as I understand it is officially reserved for the Moon, which orbits our earth. True, planets are "satellites" of the sun and satellites of planets, i.e. moons do orbit the sun along with their planets, and smaller stars in binary pairs do orbit larger stars as so too are satellites. But that's not what is to be understood when the term is seen.

As for Jupiter, yes it could be oonsidered a failed star, not because the berycenter is outside the sun, but because its mass appraches that necessary to begin deuterium burning. As it stands it falls well within the sensible definition of a planet.

cheers and regards J.H.McDonnell (talk) 00:47, 25 October 2009 (UTC)

Weasel words; Describing the reaction to the IAU definitions

As of the time I accessed this page, the second paragraph of the introduction contained weasel words. "The definition officially adopted by the IAU in 2006 has been both praised and criticized, and remains disputed by some scientists." This unsourced, weasel word claim does not belong in the introduction to a Featured Article. MathEconMajor (talk) 13:48, 27 August 2009 (UTC)

Nonesense; evem though I wouldn't rate this as a featured article in the first place. Interesting, informative, and debative maybe J.H.McDonnell (talk) 00:29, 25 October 2009 (UTC)
I know it has been criticised, f.ex. by Alan Stern, I also believe the definition has been defended, f.ex. by the Eris discoverer Mike Brown, so the statement is simply true. Although a few more citations would make the support for the statement better. ... said: Rursus (mbork³) 15:50, 8 December 2009 (UTC)
The fact that, after 3 years of criticism, the next IAU Congress apparently didn't even discuss changing the definition suggests it's been accepted by most astronomers. It seems reasonable to mention opposition, but not to give it any sort of equal treatment. Peter jackson (talk) 10:51, 9 December 2009 (UTC)
I believe you're wrong about it being "accepted". The troubles will occur when major exoplanets that haven't cleaned up their orbits will be discovered. I think that most astronomers find the definition only being an "administrative one", not touching their research and being a futile thing to discuss. Nevertheless, we can await future troubles silently too. Rursus dixit. (mbork3!) 16:52, 28 January 2010 (UTC)
The line between a protoplanet (still undergoing significant growth and and clearing its orbit) and a grown-up planet will always be somewhat blurry. For example, when exactly did Jupiter move from a protoplanet to a planet? You could base an answer on mass, how clear Jupiter's orbit is, or how clear the solar system is as a whole. -- Kheider (talk) 18:28, 28 January 2010 (UTC)
I don't think Rursus' remarks contradict mine. There can be various sorts of & reasons for acceptance. Peter jackson (talk) 14:34, 29 January 2010 (UTC)


For some reason, when the table is sorted from most massive to least, Saturn comes first. The list works when sorting in the other direction, though. (talk) 22:46, 1 September 2009 (UTC)

Not in my browser. Either there was some trouble that have been fixed, or the trouble is still there, but doesn't occur in the Gecko engine (same as Mozilla Firefox) on Epiphany 2.22.3. The sortable tables are implemented in JavaScript/JScript/EcmaScript, and the behavior might vary depending on bugs in the WWW browser used. In the later case: just wait and upgrade your browser to get the old bugs substituted for brand new ones. Exciting, isn't it!? ... said: Rursus (mbork³) 15:55, 8 December 2009 (UTC)


In the section History of the concept, second paragraph:

In the 1990s, astronomers began to find objects ...

and later same paragraph:

Several terms including minor planet, subplanet, and planetoid started to be used for the bodies now known as dwarf planets.

gives the reader a very distinct impression that the terms minor planet etc. were starting being used after 1990, which is of course quite wrong: at least the terms minor planet and planetoid were used maybe starting in the 19th century as aliases for asteroid. The trouble is, that if the terms are to be introduced at that place in the paragraph, the grammatical verb tense must be Present perfect tense or Pluperfect tense to indicate that the terms were coined early in the place where they're mentioned. Rursus dixit. (mbork3!) 17:03, 28 January 2010 (UTC)

Yes, those terms were both used in the early 19th century. Peter jackson (talk) 17:37, 28 January 2010 (UTC)

Eris link

I believe the link in the "Eris" image would better point to: Eris (dwarf planet), instead of simply Eris. thanks. —Preceding unsigned comment added by (talk) 10:54, 18 February 2010 (UTC)

 Done. -- Kheider (talk) 11:15, 18 February 2010 (UTC)


Is it actually so hard to keep it consistent even inside of one article? The tables have somewhat different facts; Current members section tables vs Prime plutoid candidates table. Pluto's stats are close enough, but
-Haumea has 1050-1400 for diameter and 41-43 for mass in the first, 1436 and 40 in the latter.
-Makemake has 45.79 for distance and ~40 for mass (first), 45.3 and 30 (latter)
-Eris 67.67 for distance and 2300-2500 for diameter (first), 68.0 and 2600 in the latter.
Which ones are the right? The Current members section's 'Physical attributes' table has two citations marked for each, so those could be the right ones... (talk) 22:49, 27 September 2010 (UTC)

The orbits will vary based on the epoch used to retrieve the data and to a less extent orbital refinement as a result of larger observation arcs. Pluto varies somewhat less simply because it has a better determined orbit and whips around the Sun relatively fast and stable 3:2 resonance. Using a 1954 epoch Eris has a semi-major axis of 67.7, using a 2010 epoch you get a semi-major axis of 68.0. Makemake: 1995=45.79 and 2010=45.3. The orbital values are not fixed numbers with only one correct solution. -- Kheider (talk) 06:39, 28 September 2010 (UTC)


I've ran WikiCleaner through this and simplified a lot of redirects (piping them), so if there's any problems with them, just go-ahead and fix them.
--George2001hi (Discussion) 18:17, 15 October 2010 (UTC)


About a quarter of the asteroids are known to be spherical because they are presumably loose rubble remaining from outgassed comets and/or gravitational aggregations of smaller asteroids, or collision fragments, etc. Are they all technically dwarf planets under the present definition? Ginger Conspiracy (talk) 21:06, 14 November 2010 (UTC)

It would appear not. They'd still have to clear an orbit, & most asteroids aren't in "clean" orbits. TREKphiler any time you're ready, Uhura 21:36, 14 November 2010 (UTC)
A quarter of the asteroids are known to be spherical? You would need a reliable reference for that statement. As far as I am aware most asteroids when viewed up close are irregular in shape. Needless to say, even if some asteroids are spherical, very few are massive enough to be in hydrostatic equilibrium. -- Kheider (talk) 23:08, 14 November 2010 (UTC)
Actually only Ceres is spherical. Vesta and Pallas are nearly spherical but not completely. All other asteroids are highly irregular. Ruslik_Zero 19:05, 2 December 2010 (UTC)
Vesta was almost certainly once in equilibrium, given that it has a basaltic surface. The question is whether that's enough to qualify it as a DP today. — kwami (talk) 21:14, 2 December 2010 (UTC)

wait, what?

"The classification of bodies in other planetary systems with the characteristics of dwarf planets has not been addressed,[10] although if they were detectable they would not be considered planets." If a body in another planetary system is detectable, it would not be considered a planet? (talk) 06:38, 11 December 2010 (UTC)

It means a "dwarf-planet-like body" in another system would not be considered an (exo)planet, not any body.--Roentgenium111 (talk) 15:33, 11 December 2010 (UTC)

Reference list

I suggest the implementation of {{Reflist|colwidth=45em}} on this article, because of the length of the reference list. Opinions, rejections? —bender235 (talk) 10:51, 16 December 2010 (UTC)

Would you prefer me to take it back? I can if you want, it just wasn't registering as double-columned. :) -That Ol' Cheesy Dude (talk)
Whether {{Reflist|colwidth=45em}} produces double-columns depends on your screen size.
Given the fact, that most of the references are very long, {{Reflist|2}} should not be used because a smaller screen resolution (1024x768 and smaller) would produce too many line breaks. —bender235 (talk) 18:08, 1 January 2011 (UTC)

Definition: Orbiting the sun, or a sun/star?

The article begins with A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun. Is that the precise wording? If so, similar objects in other solar systems would be excluded. Is that correct? samwaltz (talk) 18:39, 16 December 2010 (UTC)

Technically, there is only one Sun (the star at the center of the Solar System). For other planetary systems there are currently only planet-like bodies and asteroid-like bodies. Heck even now masters and apprentices do not agree on the exact definition of a comet. :) -- Kheider (talk) 19:01, 16 December 2010 (UTC)
I'm pretty sure that was the wording used. At the time, I don't think anyone was really thinking about other solar systems. Given the problems we have detecting larger bodies around other stars, it doesn't seem likely that the question would be relevant. If/when such bodies are found the definition would probably be amended as your title suggests. --Khajidha (talk) 19:03, 16 December 2010 (UTC)

No new dwarf planets?

Eris was discovered five years ago and there have been no other dwarf planets since then? Does this call the definition into question again? Algr (talk) 16:55, 1 November 2010 (UTC)

Astronomers are basically finished searching from the Northern hemisphere, and are just now getting started with a Southern hemisphere search. There is no scientific need for non-dominant bodies like Eris, Pluto, or for that matter our moon to be full fledged planets. -- Kheider (talk) 17:07, 1 November 2010 (UTC)
And don't forget there are dwarf planet candidates. Rothorpe (talk) 18:31, 1 November 2010 (UTC)
Why would the number of dwarf planets call the definition into question? Since there is a fairly small window into which an object can fall to be called a dwarf planet, I would expect a fairly low number of them to exist. --Khajidha (talk) 18:48, 1 November 2010 (UTC)
Under the current definition, Jupiter would be classified as a dwarf planet if something larger drifted into it's orbit. One of the main arguments for demoting Pluto was that not doing it could result in 100 planets in our solar system. But it seems that that isn't going to happen. And in any case, there used to be 4 natural elements, and now there are over 100, but no one started insisting that atoms have to clear there outer orbits of electrons to be elements. Algr (talk) 17:39, 2 December 2010 (UTC)

There are many dwarf planet candidates and we will probably never know exactly how many of them are ~600km in diameter and in hydrostatic equilibrium. We will probably NEVER discover all of them since some of them will be near their farthest point from the Sun and will be very difficult to detect, much less study in detail. Dwarf planet candidate 2010 EK139 with an absolute magnitude of 3.8 would be the most notable discovery this year and might be a dwarf planet. Anything larger than Jupiter crossing Jupiters orbit would make the Nibiru collision look like nothing. -- Kheider (talk) 18:34, 2 December 2010 (UTC)
What he said. Also, the example of the natural elements doesn't really apply here. Individual elements are discrete things while planets, dwarf planets, small solar system bodies, etc are terms. They exist only as divisions along a continuum of objects. You may not like where the IAU has drawn those lines but they at least give reasons for those definitions. The "Pluto is a Planet" movement has not come up with any rationale that would keep Pluto on the list but exclude the other dwarf planets (which the Pluto boosters don't consider planets). --Khajidha (talk) 16:14, 16 December 2010 (UTC)
If something did come along and eclipse Jupiter and do as you propose, then of course you'd have to rethink things. However there isn't any evidence of that sort of occurrence happening. You can only classify what you have seen. (talk) 16:57, 19 May 2011 (UTC)

PLuto I've been told is a dwarf planet. Unfortunelty cause I have to learn the order of planets again. Now Has anyone heard of Planet X and is that a dwarf planet? (talk) 22:57, 16 December 2010 (UTC)

Planet X is indeed a Dwarf Planet. It was officially named Eris (talk) 16:57, 19 May 2011 (UTC)
I should add that by Planet X, i assumed you meant the Tenth Planet found as reported in the mid 90s as opposed to the object that astronomers were searching for for over a century earlier, which they now believe doesn't exist (talk) 16:40, 20 May 2011 (UTC)

Equilibrium vs. differentiated interior

I was wondering, is there, from a theoretical perspective, a link between achieving hydrostatic equilibrium and the formation of a differentiated interior? The section on Size and mass suggests there is, but it isn't spelled out anywhere. --JorisvS (talk) 20:22, 24 June 2011 (UTC)

There's a link, but I'm not sure we know how robust it is. Pallas is partially differentiated, or so we think. Vesta should be; maybe we'll have better answers in a couple months. — kwami (talk) 18:03, 4 July 2011 (UTC)

Table "Physical attributes of dwarf planets"

The entry for Haumea seems a bit problematic. The issue probably has to do with its ellipsoidal shape. If you plug in 1150 km as the diameter of the dwarf planet, and use a density of 2.6-3.3 g/cm^3, you get a mass of 2.8-3.5% of the Moon's mass -- not 5.7%.

Incidentally, what does "diameter" even mean for an oblong body like Haumea? Does it mean the diameter that a spherical body would need to have, given its suspected albedo, in order to be as bright as it is? Would it not make sense to give the dimensions 1,960 × 1,518 × 996 km, or at least take their average in some way? Maybe there's a way to briefly explain this, as a footnote to the table. Kier07 (talk) 17:03, 3 August 2011 (UTC)