Talk:Dwarf planet/Archive 7

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Archive 1 Archive 5 Archive 6 Archive 7 Archive 8

Extrasolar Dwarf Planets can't exist ??? Huh ?? Too Solar centric ...

I have an issue with the definition in this article. I mean, there are possibly numerous of these objects in our Solar System. One would imagine that there would be countless of these in the galaxy. But the fact that only those orbiting the Sun can be classified seems ridiculous. How is it possible to observe that exodwarf planets have cleared their orbital neighbourhood or that they have achieved hydrostatic equilibrium ? Shows just how flawed the definition is. Once Mercury sized objects are found orbiting a star, there seems to be no way of telling whether it is a dwarf planet or not (and therefore a planet). Recently confirmed KOI-961.03, not much bigger than Mars could well share its orbit with large planetesimals. We will never know and they will likely remain planetary candidates forever. --EvenGreenerFish (talk) 13:14, 22 January 2012 (UTC)

Please read WP:NOTFORUM. However, the IAU has released two different definitions. One for extrasolar planets and one for the Solar System. In their definition of extrasolar planets, which sets an upper limit for size, it specifically states that the lower limit would be the same as that defined within the Solar System. So basically they said that yes, extrasolar dwarf planets do exist. Serendipodous 13:34, 22 January 2012 (UTC)
Don't shoot the messenger, I'm just calling it as I see it. There is absolutely no reference to "extrasolar" in this article whatsoever. So I'm not the IAU, but just because the IAU defines it one way doesn't mean it makes sense or that the differentiation shouldn't be addressed somehow here. The article should mention that there are two separate definitions. I'm not a mind reader and don't certainly don't expect that other readers would be either. Anyway two separate definions ? IMHO thats absurdly redundant. --EvenGreenerFish (talk) 11:58, 23 January 2012 (UTC)
Do you have a ref for that? In the lead here we say that this has not been addressed. — kwami (talk) 03:29, 23 January 2012 (UTC)
here. Serendipodous 09:24, 23 January 2012 (UTC)
Thanks. I've removed that section from the lead, as this (which was the ref used there) does not support the claim. We'd said:
"although if they were detectable they would not be considered planets."
Since DPs meet the mass requirement for planets, they definitely do not say that. — kwami (talk) 10:09, 23 January 2012 (UTC)

reason for criticising IAU def

Ckatz reverted my rewording of the reasons for criticizing the IAU def of planet, but his "more accurate" wording is unclear. Ruslik, for example, seemed to think that Stern objected to Pluto being classified as a DP. Actually, it was Stern who proposed the term DP for bodies like Pluto. What he (and others) have objected to is the exclusion of DPs from planetary status. AFAIK, that is the only sig. critique: others, such as the potential ambiguity of 'clearing the neighborhood', are just consequences of this exclusion. — kwami (talk) 10:04, 23 January 2012 (UTC)

Moving on

Okay, the RfC has expired with no-one new commenting on it.

Do we agree on anything that we didn't before, so we can settle this ourselves? — kwami (talk) 09:00, 13 February 2012 (UTC)

Kwami, it seems pretty clear to me (and to others, based on the comments on this page) that there just is not support for the changes you want to make, nor for the manner in which you have been editing. It would appear that the only way we can properly move forward is for you to recognize that and accept it. --Ckatzchatspy 09:26, 13 February 2012 (UTC)
Seconded. Serendipodous 09:29, 13 February 2012 (UTC)

Besides the fact that there is support, please read WP:democracy. This article has blatant NPOV issues, as demonstrated with multiple RS's. If we cannot work out how to properly follow WP policy together, then we need to go further up DR, presumably to arbitration. The main issue is that the table in this article not be divided artificially, that we not equate the IAU with WP:truth, but only treat it as a widely respected RS. More important than other sources, but not the only professional opinion. — kwami (talk) 09:57, 13 February 2012 (UTC)

Kwamikagami, the consensus is that the dp articles have been adequately modified to reflect the sources, even if YOU do not like how they read. Please quit beating a dead horse.-- Kheider (talk) 11:27, 13 February 2012 (UTC)
Not as long as we violate NPOV. The 'consensus' is evidently based on too narrow a sample of editors. — kwami (talk) 11:58, 13 February 2012 (UTC)
Kwamikagami, you are going to find the "Joe Q. Wikipedia" does not care for the needless POV editing. We do reflect our sources and I am sorry that you feel that so many dwarf planet / planet articles are biased. Since August 2011, you have FAILED to get a consensus to make major changes to the dp articles. All the "probable dp" articles have been edited to include the sources without making out right claims. Can you please just drop the subject for 6 months and may be there will be some new sources to work with. Everyone following this "6 month debate" has grow tired of going in circles because YOU are not satisfied with the wording. -- Kheider (talk) 13:46, 13 February 2012 (UTC)
I wholly agree. Kwami, please, drop the stick and back slowly away from the horse carcass. Ruslik_Zero 18:22, 13 February 2012 (UTC)
Kwamikagami, please take your concerns to a Wikipedia:Dispute resolution page. The majority are tired of the same group (pro or negative) saying the same thing since August 2011. -- Kheider (talk) 01:22, 24 February 2012 (UTC)
I think all of the editors involved here should refrain from contributing to this page. Clearly this is an edit war and since the issue cannot and should not be resolved on Wikipedia by just two people, or one admin (Ckatz) who has clearly ganged up on another, they need to leave it alone and take a break from editing. Kwami is not necessarily to blame here, as Ckatz has a history of repeatedly edit warring and stalking certain pages. He may need some counseling or help. Does Wikipedia have a psychological counseling resource for over zealous admins? Maybe they need one. - Catpowerzzz (talk) 17:51, 24 February 2012 (UTC)
I disagree. CKatz has a history of vociferous editing but at heart here is Kwami's inistance that his point of view be heard above all others. I have deliberately stayed away from this discussion because I do not believe it will be resolved outside of arbitration, an opinion others involved in this dispute do not yet hold. However, much as I respect Kwami as an editor (and I do, very much) I think he has overstepped himself in his obsession with pushing his POV in this dispute, which is not only esoteric and virtually incomprehensible to anyone who hasn't been studying the topic for the last 6 years, but would place Wikipedia in the position of taking a stand in a still-unresolved argument among astronomers, which it should not do. Serendipodous 17:58, 24 February 2012 (UTC)
I wouldn't take "Catpowerzzz" too seriously, given that it is an account used primarily for COI-based editing of articles in a few specific areas. The post here is simply an attempt to stir up trouble due to an unrelated matter, as evidenced by the edit summary suggesting that Kheider agrees with keeping the POV tag and by a random tagging of the article on Ceres. --Ckatzchatspy 19:18, 24 February 2012 (UTC)
I agree with Serendipodous that Kwami's POV concerns can not be resolved without escalating it to arbitration. I have done my best to to try and find a reasonable compromise between the two extremes. When we find new sources we can move forward, in the meantime, I do feel the POV tag on this featured article is pointless to the general public. -- Kheider (talk) 19:36, 24 February 2012 (UTC)


There is a tag in the lead reading "cite petition here". The petition website www.ipetitions.comSLASHpetitionSLASHplanetprotestSLASH is blacklisted as spam. So, I don't think it can be linked directly. DrKiernan (talk) 19:16, 13 February 2012 (UTC)

The actual signature page from that site is here. It's letting me link here on this talk page.
And here's the press release for the petition itself: [1]kwami (talk) 00:20, 14 February 2012 (UTC)


In a nutshell, I'm at a loss as to what to do about him. I honestly think that the astronomy editors have tried to work with him and listen to him, and to try to work aspects of his concerns into the article text. However, it really feels like an "all or nothing" scenario here; he insists on maintaining a "POV" tag on this article, he's refusing to heed the results of numerous RfCs, and he's now rewriting the leads of Sedna et al again. There has to be some way to stop the damage that is being done to dwarf planet - related articles. --Ckatzchatspy 08:12, 5 June 2012 (UTC)

Take this to arbitration. Simple. Serendipodous 10:58, 5 June 2012 (UTC)
This is his standard operating procedures. He's butted heads with many many different groups of users, but being an admin, he seems to come up on top. (talk) 11:07, 5 June 2012 (UTC)
The general Wikipedia community does not care about this "basically meaningless" POV-war that has been going on since August 2011 between 4-10 of the top dwarf planet article editors. I agree that the tag has been on there long enough and should simply be removed. -- Kheider (talk) 13:12, 5 June 2012 (UTC)

Ckatz, the only reason you gave for opposing the edit at Sedna was that I was the one making it. Really, is that all it is? I've posted that edit for discussion below. I wouldn't think something this trivial would require discussion, not without someone at least giving a pertinent reason for opposing it.

I would say that you've refused to heed the RfC's, since several people have objected to your refusal to follow sources other than your preferred authority, and you ignore them.

Arbitration is where it is probably heading, but I've been too busy to address it right now.

As for editors trying to work with me, yes, Kheider has, and we were able to come to agreement on most things. You have not. I suspect that has to do with a fundamental disagreement on the role of authority in science or maybe in an encyclopedia. — kwami (talk) 23:12, 5 June 2012 (UTC)

This dispute will resolved in a much simpler way that you think. As time passes by the Brown's blog will become too dated to be useful. It has already become pretty useless as a source of the information about sizes of large objects—it has not been updated since the last summer despite all claims to contrary. In future it will be considered only as a historical curiosity. Ruslik_Zero 18:23, 6 June 2012 (UTC)
Still more recent than the IAU. Also, Brown isn't our only source. He will become dated only when we have more recent expert evaluations of whether or not these bodies are DPs. — kwami (talk) 21:14, 6 June 2012 (UTC)
No, Brown's blog if not updated will become irrelevant and forgotten in a few years whereas IAU statements will continue to be cited for many years. Ruslik_Zero 08:43, 7 June 2012 (UTC)

Wording in individual articles

This is a trivial point, which I would think would be uncontroversial, but I'm getting unexplained pushback, so I guess it requires discussion.

For the Tancredi/Brown DPs, we currently say that they are not "formally designated" as DPs by the IAU. However, we have no source that the IAU is in the business of formally designating DPs; the wording NASA uses in one of Ckatz's refs is "recognized". I therefore propose changing the wording to not "recognized" as DPs by the IAU. I think that sums up the situation without implying anything we can't justify.

Any objections? — kwami (talk) 23:05, 5 June 2012 (UTC)

Yes - why are you bringing this up once again? Can we not avoid stretching this dispute across every DP-related article in Wikipedia? --Ckatzchatspy 23:11, 5 June 2012 (UTC)
I've never brought it up before. I thought the wording could use improvement; it's basically copy editing, normally too trivial to discuss. I take it you have no actual objection, then? (It's a lot easier to take your objections seriously if you give a reason for them.) — kwami (talk) 23:14, 5 June 2012 (UTC)
I've never brought it up before. Surely you jest? The "recognized"/"candidate" vs. "official" issue has been the dominant discussion topic here and on other DP-related pages for almost a year. siafu (talk) 19:38, 6 June 2012 (UTC)
The topic has been whether we follow multiple sources or just the IAU. No-one disputes that only the five are recognized by the IAU; so, is there any reason not to word it that way? — kwami (talk) 20:29, 6 June 2012 (UTC)
There are multiple secondary sources (which are preferable over primary sources according to WP:V) that cite IAU. Can you point me to at least one serious secondary source that cites Brown's blog? Ruslik_Zero 08:46, 7 June 2012 (UTC)
What's this obsession with Brown's "log"? We're talking about using the wording of Ckatz'z NASA reference. — kwami (talk) 18:06, 7 June 2012 (UTC)
Please stop referring to the NASA page as "my" reference. You're the one trying to make this change, yet again. --Ckatzchatspy 18:11, 7 June 2012 (UTC)
You provided the ref. As for it being "yet again", you're the one who wanted that! You told me to bring it up here, so here I am. Do I take it there is no problem with the edit, only with the editor? — kwami (talk) 19:22, 7 June 2012 (UTC)

So, Ckatz, what is your objection to the proposed wording? --JorisvS (talk) 10:50, 9 June 2012 (UTC)

I'm not sure exactly which reference Kwami is talking about, but I did find a small NASA DP web page that uses the phrase "recognized". However, Tancredi's paper (doi:10.1017/S1743921310001717) uses the term "officially classified", which I think is closer to "formally designated". Could you split the difference and say "formally recognized" or "officially recognized"? Tbayboy (talk) 15:32, 9 June 2012 (UTC)

"Formally recognized" works for me. — kwami (talk) 15:35, 9 June 2012 (UTC)
Jorvis, the issue lay in watering down the wording with respect to "official" status, contrary to what we have discussed here and elsewhere. As long as we present something that reflects the IAU as category maintainer, it should be OK. --Ckatzchatspy 05:33, 10 June 2012 (UTC)

Observed DPs

In the lede, there is the following sentence: "However, only two of these bodies, Ceres and Pluto, have been observed in enough detail to demonstrate that they fit the definition." This is not sourced, nor is the similar statement in the article's body supported by a reference. I know this sentence has been around for several years, and with, at least, the occultations of Haumea by Namaka, and the stellar occultation by Makemake this may not longer be the case. Does anyone know more about this? --JorisvS (talk) 20:06, 25 July 2012 (UTC)

Haven't heard of any observations of the predicted occultations of Haumea, and we don't mention any in the article. We also don't cite stellar-occultation data for the diameter of Makemake. Have we just been lax in updating the articles?
Sheppard et al. (2011) wrote, "Though the dwarf planet definition is imprecise, it is clear that Ceres in the main asteroid belt as well as Pluto and Eris in the outer solar system are bonafide dwarf planets. Makemake and Haumea are also likely dwarf planets as are the next largest bodies in the outer solar system such as Sedna, 2007 OR10, Orcus and Quaoar."
That suggests that as of last year, the point in question in the lead hadn't changed. (AFAICT, Eris is assumed to be in HE because it's more massive than Pluto, not measured to be.) — kwami (talk) 21:10, 25 July 2012 (UTC)
The statement still isn't sourced. Practically, that doesn't bother me, because the combination of evidence is overwhelming -- visual alone for Ceres, mass and visual for Pluto. Pedantically, is the visual evidence alone for Pluto more certain than for Vesta? I.e., is the visual evidence for Pluto good enough that a Vesta-scale deviation from H-E would be detectable? The Pluto image shown on the page is the result of heavy image processing, not a direct image. Did that processing assume H-E (a reasonable assumption because of the mass)? Well, we'll know for sure in three years. :-) Tbayboy (talk) 02:14, 26 July 2012 (UTC)
In our previous discussions we've had other sources that Pluto is known to be in HE through direct observation. Remember, we observed many many mutual occultations with Charon, enough to determine the shapes of both worlds. — kwami (talk) 03:07, 26 July 2012 (UTC)
Not according to [2] Even with occultation, the error bars are large because of the atmosphere. Is an 90 km deviation over ~2300 enough to not be H-E? Please note that I'm not suggesting you remove the sentence, just that I agree with JorisvS that there should be a source. Tbayboy (talk) 03:40, 26 July 2012 (UTC)
Agreed. There are some around somewhere.
I doubt it's a 90-km deviation, but a 90-km uncertainty. AFAIK, no indication of irregularity. — kwami (talk) 04:35, 26 July 2012 (UTC)
There is no material difference between uncertainty and deviation. Ruslik_Zero 10:24, 26 July 2012 (UTC)
Sure there is. You can measure that s.t. is not the same relative size in all directions without being certain of its absolute size. Here one of the problems is whether we're measuring to the limb of the world or to the haze in its atmosphere. — kwami (talk) 10:55, 26 July 2012 (UTC)
No you can not. If the absolute size is known with uncertainty δ you can only be certain that it is the same in all directions with the same uncertainty. Ruslik_Zero 19:28, 29 July 2012 (UTC)

Given the intricacies involved the statement really should be properly sourced. I can't find results of the Haumea–Namaka occultation, even though this poster by Brown (among others) talk about the occultations and that it could constrain Haumea's shape to within ~20 km. They did not conclusively detect any but talk about follow-up observations. That was several years ago. --JorisvS (talk) 09:43, 27 July 2012 (UTC)

There were severe observational difficulties, esp. w the limited equipment they could get. There were also sig. uncertainties in the predicted eclipses. Perhaps they never did detect anything. — kwami (talk) 12:50, 27 July 2012 (UTC)
Well, I would think more would be known about this by now. --JorisvS (talk) 13:14, 27 July 2012 (UTC)
Negative findings tend to not get published. (A real problem w medical & toxicological metastudies.) — kwami (talk) 13:51, 27 July 2012 (UTC)
Even though they can be just as (or more) interesting... --JorisvS (talk) 13:59, 27 July 2012 (UTC)

I've now tagged the relevant statements in the body of the article. --JorisvS (talk) 12:06, 29 July 2012 (UTC)

Vestan equatorial diameters

"[...] but even so its equatorial diameters are not equal as they would be under equilibrium, and as they are for Ceres." Where was it written to imply what this sentence implies here: that this is part of Vesta not being a DP? And would Vesta's short rotation period of 5.342 h (compared with 3.9155 h for Haumea and 6.34 h for Varuna) not be enough to make the equatorial diameters different? --JorisvS (talk) 13:04, 18 August 2012 (UTC)

Unless someone can present an argument for this statement, I will remove it. --JorisvS (talk) 21:16, 22 August 2012 (UTC)
Maybe Vesta's high density and relatively small size might require a faster spin rate than Haumea or Varuna to elongate (under H-E), so the first part of the statement could be correct, but it's not so obvious as to stand unsupported by a reference. I don't see how the comparison to Ceres has any relevance. Tbayboy (talk) 14:32, 23 August 2012 (UTC)
Exactly. I suspect the comparison with Ceres was meant to strengthen the unequal equatorial diameters as an argument for Vesta not being a DP. --JorisvS (talk) 21:08, 23 August 2012 (UTC)

I've removed it. --JorisvS (talk) 22:20, 26 August 2012 (UTC)

Quaoar's size

We still have the outdated value of 890±70 km as Quaoar's size in this article, even though the longest measured chord (but not equatorial diameter) from 2011 was 1170 km. How shall we address this? --JorisvS (talk) 10:10, 15 August 2012 (UTC)

The chords suggest it is elongated, so there might not be much difference. Tbayboy (talk) 16:09, 15 August 2012 (UTC)
Which then begs the question: Why is it elongated? --JorisvS (talk) 16:18, 15 August 2012 (UTC)
See Emily Lakdawalla's report (paragraph 6), as well as the chord results brief that's referenced in Quaoar. The chord results are strange. Tbayboy (talk) 18:11, 15 August 2012 (UTC)
Is there a picture of the chords somewhere? --JorisvS (talk) 18:32, 15 August 2012 (UTC)
I haven't seen/read any more about the chords (other than another similar media report, I forget where). I don't trawl abstracts, so maybe there's something, but I've assumed it's because they haven't published because they are still working on trying to figure it out. Tbayboy (talk) 22:51, 15 August 2012 (UTC)
About a later occultation: [3], where the occultation by Quaoar was seen from France and Switzerland and the occultation by Weywot could be seen from somewhere in central Africa. The preliminary chords of Quaoar are [4]. --JorisvS (talk) 10:21, 17 August 2012 (UTC)
Those chords seem to agree with a spherical shape (if one discards # 3 and 4; obviously two of # 2—4 must be quite erratic). Here's a report about an even later occultation (7/2012), specifically mentioning the need to determine the shape... --Roentgenium111 (talk) 00:36, 30 August 2012 (UTC)
Strange indeed. The first link states that they could not rule out a contact binary - that surprises me, shouldn't contact binaries be impossible for dwarf planets? As soon as the two parts touch (or even slightly earlier), they should re-form into a single hydrostatic equilibrium body AFAICS... --Roentgenium111 (talk) 19:26, 15 August 2012 (UTC)
That's what had me wondering, too. Nor is Quaoar a fast rotator... --JorisvS (talk) 22:31, 15 August 2012 (UTC)

Table titles

Ckatz: "the section title says "official" simply to differentiate from non-official"

Exactly. And the tables separate official from non-official. They therefore need to say that, as readers skimming an article will see the tables without reading all the intervening text. It's not "wordy", it's precise. If you want the simpler title, then we should be logically consistent and put all of the bodies in it. If we separate the tables, we need to separate the titles accordingly. — kwami (talk) 05:52, 16 August 2012 (UTC)

Perhaps I should clarify. The section heading says "official" because we need a term in there to contrast with "nearly certain". We could certainly say "dwarf planets and nearly certain dwarf planets", but it's less wordy if we avoid the double DP (and IIRC you wanted the "official" in there). We could also use "dwarf planets and candidates", but I seem to recall that you don't like that either. With respect to the tables, we already imply an official status simply by saying "dwarf planet" in the first table, a point emphasized by the use of "nearly certain" in the next one. --Ckatzchatspy 06:24, 16 August 2012 (UTC)
Logic dictates just the opposite. "Dwarf planet" in no way implies official status, it only implies that they're dwarf planets. We could not say "dwarf planets and nearly certain dwarf planets", that would be like having one table for "Christians" and a second for "Other Christians". Or mammals and primates. Or felons and suspected felons. (Convicts and suspected felons would work, since 'convict' predicates official recognition.) Here we have a list of candidates, 5 of which have been accepted by the IAU. Whether a body is a DP has nothing to do with whether it is official; we defer to IAU recognition, but that doesn't mean that the other candidates are or are not DPs.
You're concerned about the 'wordiness' of adding a single word. But the cost is falsely labeling the table, on the assumption that everyone will have read the text and know not to take the title literally. Why not just say what we mean, as one would expect of a reference work? — kwami (talk) 08:19, 16 August 2012 (UTC)
The 'dwarf planet' in the upper two tables definitely needs a qualifier. I've therefore added 'official' to them. If someone knows a better qualifier, then please suggest it or change it. I'm not yet certain how to change the misleading qualifier '"nearly certain"' in the lower two tables. --JorisvS (talk) 14:40, 17 August 2012 (UTC)
Neither qualifier is ideal, but they're better than nothing. "Official" is bizarre because science is not decided by what is official. "Nearly certain" is odd because it applies to several "official" DPs. IMO we should list them in a single table and source who accepts them, just as we would with any other astronomical bodies. — kwami (talk) 21:16, 17 August 2012 (UTC)
How about "recognized"? --JorisvS (talk) 09:25, 18 August 2012 (UTC)
I like that better. Of course, it begs the question 'recognized by who?', since the others are recognized too. That would be resolved by putting them all in one table and adding a column for IAU recognition, but your suggestion is superior to what we have now. And maybe the section title could be simply "recognized dwarf planets". — kwami (talk) 22:34, 18 August 2012 (UTC)
Then how about "IAU-recognized"? --JorisvS (talk) 12:24, 19 August 2012 (UTC)
Perfect. — kwami (talk) 12:58, 19 August 2012 (UTC)
They are not "IAU-recognized". They are recognized by the vast majority of the astronomical community as apposed to others. Ruslik_Zero 13:09, 19 August 2012 (UTC)
But that's only because of the formal recognition by the IAU... --JorisvS (talk) 13:23, 19 August 2012 (UTC)
No, IAU would have never recognized them if their had not been such a consensus. Ruslik_Zero 14:36, 19 August 2012 (UTC)
If the IAU were to recognize Quaoar today, that would be reported in general texts as well. Remember, the current cutoff was made for naming purposes. Also, the general consensus for the 5 is implied by noting they're recognized by the IAU, and clarified if need be by the text. — kwami (talk) 18:45, 19 August 2012 (UTC)
The "naming purposes" cutoff does not mean that Haumea and Makemake are not fully accepted DPs. The IAU press releases declare them DPs with no hedging (i.e., no "for naming purposes only" disclaimer). We don't know what considerations went into their declaring them DPs, whether it was just H < 1 or whether they also considered other data. Tbayboy (talk) 14:06, 20 August 2012 (UTC)
The point though is that they are recognized by the IAU, while the others are not. That is the citable difference, since we don't have a count for the % of astronomers who recognize any of these. Since the IAU is the closest there is to a standard, IAU recognition implies wider recognition, so your point is covered. The current wording, though an improvement, is still factually incorrect: we have refs that the IAU five are nearly certain, and that the other four are recognized. — kwami (talk) 23:45, 2 September 2012 (UTC)

Minimum diameter

I have tagged the reference of "absolute magnitude brighter than +1 (and hence a mathematically delimited minimum diameter of 838 km)" for failed verification. The source does not say what is claimed, only that with H=+1 and p=1.0 gives a diameter of D=838 km. The geometric albedo p can be higher than 1, e.g. Enceladus has a geometric albedo of p=1.375. --JorisvS (talk) 13:27, 18 August 2012 (UTC)

I think the (now dead) IAU reference stated only the "H<1"requirement, not any corresponding minimum diameter. Presumably someone added the diameter value assuming albedo to be always <1. Are you sure the measured/assumed values for TNOs are those for geometric albedo? (E.g. the Bond albedo seems to be always <1.) If yes, is there an actual maximum value >1 for the geometric albedo which would allow calculation of a minimum diameter? --Roentgenium111 (talk) 17:59, 20 August 2012 (UTC)
PS: Here is a valid link to the IAU's magnitude requirement. This article gives the diameter value mentioned (but might have copied it from Wikipedia...) --Roentgenium111 (talk) 18:02, 20 August 2012 (UTC)
There is no maximum value for the geometric albedo. It can assume any value between zero and infinity. Ruslik_Zero 18:19, 20 August 2012 (UTC)
Having thought more about this, I don't think it can be infinite; an object cannot reflect more than the total light it receives back at zero angle, so there must be a maximum (probably very high) value for the geometric albedo, which would be reached by a hypothetical flat disc of the object's size reflecting only specularly, positioned perpendicular to the Sun. In practice, the albedo of an only specularly reflecting perfect sphere would probably be a realistic upper limit.--Roentgenium111 (talk) 17:35, 25 August 2012 (UTC)
Still, as it stands now, it is us Wikipedians assuming a geometric albedo of ≤1 even though it can be higher than 1. Just because the albedo is very likely lower than 1 doesn't make 1 the upper limit. --JorisvS (talk) 22:17, 26 August 2012 (UTC)
Yes, but since we state this assumption explicitly, I don't think it's misleading the reader. And as far as I know, no TNO is known or expected to have an albedo >1. (Eris is by far the highest with 0.99; Brown estimates albedo to be about 0.4 to 0.5 for H≈1.0 objects.) But feel free to remove the diameter estimate (or use a "more secure" upper limit for albedo, maybe 1.5?) if you think otherwise. --Roentgenium111 (talk) 13:56, 29 August 2012 (UTC)
The problem isn't that no TNO has a estimated albedo >1, but that we're talking about a minimum diameter of 838 km, which is just false because the geometric albedo can be higher than 1. How about "... brighter than +1 (and hence a diameter of 838 km for a geometric albedo of 1)."? Although, in that case I'm not sure how relevant the statement between the parentheses would be. --JorisvS (talk) 14:57, 29 August 2012 (UTC)
I see no problem with the current statement, "The IAU subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 (and hence a minimum diameter of 838 km assuming a geometric albedo of ≤1)..." The assuming is very obvious to me, and to use an albedo greater than 1 will confuse average readers. -- Kheider (talk) 15:05, 29 August 2012 (UTC)
Okay, I've come up with a very simple solution: "(and hence a diameter of ≥838 km assuming a geometric albedo of ≤1)". --JorisvS (talk) 15:19, 29 August 2012 (UTC)
"a hypothetical flat disc of the object's size reflecting only specularly, positioned perpendicular to the Sun", if it is a perfect mirror, would have infinite geometric albedo. As far as a spherical body is concerned there is no obvious upper limit either. Porous icy surfaces tend to back scatter light even if the incidence angle is not zero. Ruslik_Zero 18:32, 29 August 2012 (UTC)
Still wouldn't be infinite. The GA is a ratio of the light reflected back to the user by the object compared to that reflected back by a standard (idealised) object. Since the standard returns some fraction of the total incident light, and the perfect reflector returns only the total incident light, the maximum GA is the inverse of the fraction returned by the standard surface. Tbayboy (talk) 00:13, 30 August 2012 (UTC)
GA is ratio between the indicatrix of a perfect mirror and that of an ideal Lambertian reflector taken at zero phase angle. The former is delta function, which is infinite at zero phase angle (for a mirror positioned perpendicular to the Sun). The latter is a continuous function. Ruslik_Zero 12:25, 1 September 2012 (UTC)
(EC) Such a perfect mirror would have the same "angular brightness" as the Sun from 1 AU, which is high, but not infinitely higher than a Lambertian surface of the same size and distance; so the geometric albedo would still be finite AFAICS. --Roentgenium111 (talk) 00:22, 30 August 2012 (UTC)
This is true but only because the angular size of the Sun is finite. So, you can not position the mirror perpendiculat to the Sun. However from the practical point of view the brightness of the Sun's photosphere is so high that amounts to infinity. Ruslik_Zero 12:25, 1 September 2012 (UTC)

9 "nearly certain"

Ckatz wants this discussed. We currently say 5 are accepted by the IAU and 4 others are "nearly certain". However, what we actually have are 5 accepted by the IAU and 9 total nearly certain. Wording? — kwami (talk) 09:38, 3 September 2012 (UTC)

As an aside, it's weird that Orcus makes it in the special table when, if you look them up in the articles, Salacia is likely larger. Tbayboy (talk) 15:53, 5 September 2012 (UTC)
Well, that's our sources. Salacia is a more recent discovery. I understand the caution in wanting to be conservative about this, just not being "official", which is unscientific. — kwami (talk) 17:54, 5 September 2012 (UTC)
Well, it's not so much a question of when they were discovered (both in 2004), as it is what their absolute magnitudes are: 2.3 for Orcus and only 4.2 for Salacia. (307261) 2002 MS4 illustrates this well: It was discovered in 2002, but with an absolute magnitude of only 3.8 it suffers the same fate as Salacia. --JorisvS (talk) 22:27, 5 September 2012 (UTC)
Is Brown basing stuff just on magnitude? I'd assumed that he just hadn't updated his table for Salacia, perhaps because he wasn't involved in the recent estimate. — kwami (talk) 06:32, 6 September 2012 (UTC)
I don't know, and it's not just Salacia, though. It looks a lot like the size is a simple combination of absolute magnitude+expected albedo (larger TNOs tend to have higher albedos, the difference in albedo of cold vs. hot classicals, the bright Haumea family), except for 2002 TC302, which was measured but Brown just believes to be on the low end of the (large) uncertainty because of the anomalous size–albedo combination, despite the fact that now there are other large TNOs that have measured low albedos and that even if it is rocky the lower end would still be sufficient for it to round. --JorisvS (talk) 09:27, 6 September 2012 (UTC)
Yes, Brown just assumes a given albedo for a given magnitude unless someone has measured otherwise. The otherwise values require him to manually edit the entry. -- Kheider (talk) 09:40, 6 September 2012 (UTC)
Why hasn't he updated the albedos of Salacia, 2002 MS4, and others? --JorisvS (talk) 09:47, 6 September 2012 (UTC)
I assume he is not very active updating the page. -- Kheider (talk) 10:12, 6 September 2012 (UTC)
Yes, the website says 'last updated 27 Jun 2012'. But still, the papers were published months before that and he, at the very least, must have read them[5][6]. --JorisvS (talk) 11:25, 6 September 2012 (UTC)
Brown has never updated his list, or at least I have not noticed any changes. It remains in precisely the same state as when it was published. Ruslik_Zero 10:27, 7 September 2012 (UTC)
He has updated it multiple times, which is why we preserve an old copy for comparison when updating our own lists. — kwami (talk) 14:49, 7 September 2012 (UTC)
No, his automatic program has added new objects as they are discovered. I can not think of any human changes to the list since it was created. The list does not include (the likely dp since H=4.5) 2010 VV11 with a 2 day observation arc, and yet it includes 2007 HV90 with a 1 day obs arc. -- Kheider (talk) 16:50, 7 September 2012 (UTC)
There are frequent changes to the values of existing objects as well. Hardly matters if the changes are manual or automated. — kwami (talk) 08:05, 8 September 2012 (UTC)
I disagree. The automatic changes do not amount to much more than a modified version of Johnston's list. Manual updates hopefully add measured values that are far better than assumed values. -- Kheider (talk) 11:36, 8 September 2012 (UTC)
Measured values are explicitly stated. Few of them are measured. — kwami (talk) 22:00, 8 September 2012 (UTC)


Looks like with recent edits we are coming to an agreement on the wording, with Ckatz and I accepting much of the other's changes. The main remaining problem I have is labeling just one table 'nearly certain', when it is the bodies in both tables which are nearly certain. Since the motivation for separating them is who has accepted them, that should be reflected in the labels. I'm also dubious about calling the IAU five "official", as that is a rather unscientific POV for a scientific article. We don't speak of "official" birds or exoplanets for example. Or rather, official bird has a very different meaning, one which has nothing to do with ornithology. — kwami (talk) 22:07, 7 November 2012 (UTC)

Please, let's not revisit the :official" status of the IAU yet again; they are the body governing this,and we have hashed that out over and over again. --Ckatzchatspy 03:21, 8 November 2012 (UTC)
My objection was not about the official status of the IAU, and never has been. But I'm okay with your latest wording.
As for the table titles in your latest edit, to be true to our sources we would need to duplicate Eris, Makemake, Haumea, etc. in the 2nd table, since they are also "nearly certain" per these sources. For something closer to your wording that keeps them where they are, "objects recognized by the IAU as dwarf planets" and "objects recognized by others as dwarf planets" would work.
I separated 'by the IAU / by others' from 'orbital/physical attributes' using the table title fmt, so they wouldn't be so wordy. — kwami (talk) 04:55, 8 November 2012 (UTC)


Anyone remember the statistical review that concluded the vast majority of astronomers are okay w the IAU def of 'planet', so that it wouldn't have mattered if more people had voted? Opponents frequently complain that the vote was not representative, so would be good to include this. — kwami (talk) 23:33, 3 January 2013 (UTC)

Dwarf planet and planetoid as interchangeable terms

I've removed part of Kwamikagami's recent edit to the talk page for discussion, as I'm not yet convinced that it is accurate or even appropriate for the first sentence. The wording involved the addition of ", or planetoid,[1]" immediately following "dwarf planet" in the first sentence. First off, I can't access Brown's book to verify the context of his use of the term, and beyond that the change involved a significant restructuring of the lead that may need revision and dicsussion. Kwami, could you please not revert your material back in but instead post the relevant section form Brown's book so that we can examine it? Thanks in advance. --Ckatzchatspy 08:24, 14 January 2013 (UTC)

P. 223: "For years we've called things like Pluto and Xena [Eris] 'planetoids'—planetlike. That was a perfectly good word yesterday. But they're trying to be sneaky, they are. 'Dwarf planet' is dumb, but they need it so Pluto can become a planet with [resolution] 5B."
Sedna, of course, was announced as a planetoid. Our article has refs of Astrobiology Magazine using the term.
There is no significant restructuring of the lead. That was the only change. — kwami (talk) 08:53, 14 January 2013 (UTC)
They've also been called "protoplanets" and "planetary embryos". And "planetoid" can also be used for non-dwarf-planets -- in particular, ejected planets or DPS, and differentiated non-DPs like Vesta. Also, planetoid redirects to "minor planet". The "History..." section already mentions it, and you could add the Brown ref there. Since it's been obsoleted by DP anyway, I don't think it belongs in the lead. Tbayboy (talk) 02:57, 15 January 2013 (UTC)
"Protoplanet" has a different connotation. Evolutionary POV.
Do we know it's obsolete? We have refs postdating the IAU declaration. — kwami (talk) 03:03, 15 January 2013 (UTC)
See the Dawn mission journal. They constantly refer to it as a proto-planet.
By "obsolete", I meant amongst Brown's group, who now use DP. Tbayboy (talk) 14:24, 15 January 2013 (UTC)
The constantly refer to Vesta as a proto-planet, but Vesta is not on our list. — kwami (talk) 20:13, 15 January 2013 (UTC)
I was speaking to the "evolutionary POV". Tbayboy (talk) 03:34, 22 January 2013 (UTC)
Here's another: "A dwarf planet or a planetoid is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces ..." (Karttunen et al. ed, Fundamental Astronomy, 2007). That, BTW, is a rather successful textbook, as several of the review attest. — kwami (talk) 06:14, 15 January 2013 (UTC)
And also see the other references that Wiktionary gives, as well as other dictionaries. Also, this Nasa page refers to Hyperion as a planetoid. Tbayboy (talk) 14:35, 15 January 2013 (UTC)
Yes, "planetoid" has had a rather loose definition. But the statement that DPs are called "planetoids" is correct. We should probably add a 'sometimes' etc. so as to not imply that the two terms are always equivalent. — kwami (talk) 20:13, 15 January 2013 (UTC)
I think mentioning planetoids in the lead only leads to more confusion for the casual reader. -- Kheider (talk) 01:03, 22 January 2013 (UTC)
Okay, moved down to the name section, along w some stuff in the history section. (And moved the extra-Solar discussion out of the name section.) — kwami (talk) 02:18, 22 January 2013 (UTC)
Here's a few refs from searching "planetoid" on Nasa.
[7] and [8] refer to Vesta
[9] refers to the moon Hyperion as a planetoid
Mike Brown (I think this is also on his website), writing before 2006, says "a planetoid is any round object in the solar system that is not big enough to be considered a planet"
Also, Marsden's investigation of the relevent nomenclature has it generally used as an equivalent to "asteroid" and "minor planet"
So (along with dictionary defs and poking around RAS and a couple of others, which I didn't keep track of) there appears to be two common usages (which includes Brown's), neither of which is the same as "dwarf planet", although DP is a subset of both. Tbayboy (talk) 05:26, 22 January 2013 (UTC)
It's the same as Brown's. It's clear from context that he doesn't include moons:
What is the definition of a planet? — It is difficult for scientists to have to define a word that everybody thought they already knew the meaning of. But discoveries such as Sedna, Quaoar, 2004 DW are blurring the line between planets, asteroids, and comets. These objects are all big, so what are they? We prefer to call them planetoids. To us, a planetoid is any round object in the solar system that is not big enough to be considered a planet (actually we don't know that any of these objects are round, but it is a reasonable assumption).
'Planetoid' and 'asteroid' were synonyms a hundred years ago. But over time, 'planetoid' came to be used for larger (planet-like) objects. Using it for round objects as Brown does is the natural extension of that.
That example with Hyperion is odd. AFAIK, no-one does that!
As for Vesta, it's not clear that it isn't a DP, since it's rounded from HE; AFAIK, the issue has not been addressed since 2006.
Marsden proposes returning to the 1802 definition in conjunction with replacing DP w "planetino", but AFAICT no-one has followed this suggestion, so it's not really relevant for us. — kwami (talk) 05:41, 22 January 2013 (UTC)
Marsden surveyed and reported current use of the term, so the article (not his suggestions) are relevent. It's common to use planetoid as a synonym for asteroid, just google it. And even Brown wasn't using it as exactly DP, but in a dynamics-independent way. Tbayboy (talk) 14:08, 22 January 2013 (UTC)
The most recent citation of 'planetoid' in Marsden is 1954, so it's hardly current usage!
I've checked Google books, and almost all the top hits for 'planetoid' since 2006 are either reprints of pubs a hundred years old, WP mirrors, sci fi, or things like Metaphysics and The New Age which claims that in 1957 Earth was attacked by aliens in Orion who aimed a 'planetoid' at us. I'm not finding it in common usage as a synonym for asteroid, but we do have a well-respected textbook presenting it as a synonym for DP.
Ah, here's one: Roth (2009) Handbook of Practical Astronomy, which gives 'planetoid' as an occasional alt for 'asteroid' due to their planet-like orbits. Tinder (2007) Relativistic Flight Mechanics And Space Travel has an exercise where a spacecraft passes a "spherical planetoid", which may be the more recent (not synonymous) use.
Could you give me an example of how Brown's usage is not equivalent to DP? — kwami (talk) 19:54, 22 January 2013 (UTC)
Round moons? --JorisvS (talk) 20:01, 22 January 2013 (UTC)
No: In the 2004 Sedna article, he defines planetoids as HE objects in orbit around the Sun. That means planets too, but it doesn't appear that he ever used the term that way, and he didn't retain that aspect in 2006 or 2010. It's not how Karttunen (or anyone else, for that matter) uses it. 1800 – ca. 1950 it was used as a synonym for asteroid/minor planet; since that time (and maybe earlier) it tends to be restricted to the larger minor planets. So, some recent sources restrict it to the largest (DPs), but only after people started seeing HE as relevant to classifying objects. Anything before that of course didn't consider that aspect. It would seem that Brown, Karttunen, et al. are formalizing what is meant by 'larger' minor planet: an existing term that fits a new concept.
So I'd agree with the initial point of this thread, that planetoid and DP are not in general interchangeable terms. DP means either minor planets in HE (IAU), or non-solitary planets (Stern). Planetoid means either minor planet or is restricted to the larger MPs, and recently a synonym for DP (Brown, Karttunen, IAU draft resolution 5A). — kwami (talk) 20:23, 22 January 2013 (UTC)

arrange by orbital period?

Can we arrange the tables by orbital period, as we do in all other articles, so that people can compare them side by side, rather than by acceptance? It's still obvious who has accepted what. — kwami (talk) 00:14, 8 February 2013 (UTC)

I think the distinction is important. The article is about dwarf planets. They should remain distinct from the leading candidates. Tbayboy (talk) 04:09, 8 February 2013 (UTC)
But they are dwarf planets according to our sources, and we'd maintain the bureaucratic distinction in the list, in the intro, and in the notes for each entry in the table (we once had a column for IAU acceptance). I can't think of another scientific article where the inventory for a natural category is broken up according to sources. In List of stars in Orion, for example, all the stars are listed in one table, despite the fact that not all of them occur in every catalog. It would be ludicrous to break up the table into "List of stars in Orion according to Bayer", "List of stars in Orion according to Flamsteed", and "List of stars in Orion according to Gould", etc., and no-one would argue that U Ori isn't a star just because it isn't listed in the Hipparcos Catalogue. Yet that's what we do here. It's profoundly unscientific. — kwami (talk) 04:46, 8 February 2013 (UTC)
Distance (or orbital period) will result in splitting hairs (based on the epoch) when you list multiple objects that are in the same resonance with Neptune. I see nothing wrong with how it is currently presented. -- Kheider (talk) 10:41, 8 February 2013 (UTC)
Is it splitting hairs to arrange the moons of Saturn by distance? Why is that good enough for other articles but not for here? It will group similar orbits together: Ceres, the 2:3's Pluto & Orcus, then Haumea & Quaoar, Makemake, the SDO's OR10 and Eris, then Sedna. We already take that approach. Why would we organize them by distance, and then split them up to disrupt a straightforward comparison by distance? Rather than doing a half-assed job of that, why not just arrange them by date discovered, or alphabetically, or some other factor that's irrelevant to the bodies themselves? It makes no sense. — kwami (talk) 20:33, 8 February 2013 (UTC)
I want to assume good faith, but this honestly reads like yet another effort to blur the lines between the official DPs and the candidates. Can we please, for the sake of article stability, avoid revisiting that notion? --Ckatzchatspy 00:55, 9 February 2013 (UTC)
We're very clear about the distinction, and there are all manner of ways we could continue to make it obvious, such as the extra IAU column that JorisvS once suggested. What we have, though, is classification by source rather than anything directly to do with the bodies. "Official" isn't a scientific concept, and shouldn't be the basis of a scientific classification. This is like classifying birds by the person who named them rather than by their species, diet, or geographic range.
I have no problem with saying "these 5 are official/accepted by the IAU", and am not trying to revisit that notion. I do have a problem with unscientific organization of a scientific article. An analogous classification of the planets of the Solar system would have one table for the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn (the classical planets), and a second table for the Earth, Uranus, and Neptune (the modern planets). While that may be interesting historically, it wouldn't be a good way of presenting the planets scientifically. Similarly, having one table for "accepted by the IAU" and a second for "accepted by Brown and Tancredi" is not a scientific presentation. — kwami (talk) 05:00, 9 February 2013 (UTC)
This is the same argument as a few years ago. The [list of possible dwarf planets] is suitable for what you want. Tbayboy (talk) 23:55, 9 February 2013 (UTC)
You're suggesting that we redirect to that article, rather than simply fixing the anti-scientific bent of this article? All I'm asking is that we stop implying that it's IAU approval that makes a body a DP, when according to the IAU it's fitting the definition of a DP that makes a body a DP. — kwami (talk) 01:10, 10 February 2013 (UTC)

Ckatz, accept your rearrangements as more logical, made some of my own. — kwami (talk) 22:30, 15 February 2013 (UTC)

In Tancredi and Favre's "Which are the Dwarfs in the Solar System?", they have Eris as being a dwarf because of "case I - direct measurement of shape", together with Pluto and Ceres. Tbayboy (talk) 00:13, 16 February 2013 (UTC)

Yes, that's true. That's not the original ref, which had only Pluto and Ceres directly measured, and Eris assumed. Actually, given the recent Cassini results, we can't know even Pluto and Ceres, but I don't think anyone's addressed that yet. — kwami (talk) 05:50, 16 February 2013 (UTC)

Stars, Planets, Moons and Baricenters, or Distance Matters, Too

Under the section "Planetary Mass Moons" would it not be helpful to note that the location of a baricenter is as dependent upon the distance between the objects as it is on the difference in mass between them? The only reason that the baricenter of the Sol-Jupiter system is outside the sun is because half a billion miles separates them, whereas the only reason that it does not lie outside the earth in the earth-moon system is that the two are so close together. If Jupiter's mass were to the same ratio to the sun as the moon's is to earth, then wouldn't its baricenter with the sun be further outside the sun than it is? (talk) 16:55, 28 July 2013 (UTC)

equatorial diameters

Our diameters are not equatorial as claimed. Should they be so, or should we change the label? — kwami (talk) 02:33, 4 September 2013 (UTC)

I noticed that, too. Given the error bars on most of these, and the tri-axial shape of (at least) Haumea, I favour changing the label. It only needs to be an approximation here, anyway -- just to give an idea of the size of the object. Tbayboy (talk) 19:39, 4 September 2013 (UTC)
OK, only Ceres is still equatorial. Makemake has 2 diff diams in the same ref - which should we use? — kwami (talk) 20:36, 4 September 2013 (UTC)
They had two good fits, one circular and one elliptical, and they preferred an intermediary 1430x1502 solution. (I'm actually looking at the pre-print of the Ortiz paper, not the actual published paper.) See also "On the size, shape, and density of dwarf planet Makemake" by Brown (arXiv:1304.1041v1 [astro-ph.EP] 3 Apr 2013), a bit of a rebuttal to the Ortiz paper over the latter's density determination. Brown gets 1434x1422 (1430 as a spherical equivalent) in his analysis of the occultation data (also including other data). I think they're all in the same ballpark, so pick any one. The current 1478 actually matches the 1430x1502 as a spherical equivalent. Either seems reasonable here. Tbayboy (talk) 00:03, 5 September 2013 (UTC)

The Name Doesn't IMPLY Anything. It Explicitly States...

The Name section of the article leads off, "The term dwarf planet has itself been somewhat controversial, as it implies that these bodies are planets..."

This statement, I originally thought, was misleading, so I corrected it last week, so it said the name explicitly states that these bodies are planets, but someone undid that change. Now, I'm almost completely certain that the statement is dishonest. Let's reiterate the statement, but change a few of the details:

"The term black person has itself been somewhat controversial, as it implies that these bodies are people..."

You see the issue? To call something a "dwarf planet" is to continue calling it a planet, the same way to call something a "cotton sock" is to call it a sock or to call someone a "black person" is to continue to call them a person. The statement, "A dwarf planet is not a planet," is self contradictory. Taking away all adjectives from the sentence, you're saying, "A planet is not a planet." The thing that really scares me about this is that it leads to the bigotry in my first example. (talk) 23:15, 9 September 2013 (UTC)

Think of a dwarf-planet as a compound noun. Minor planets are not really planets either. -- Kheider (talk) 23:34, 9 September 2013 (UTC)
They also have "planet" right in the name. These names are dishonest if these bodies are really not planets. (talk) 23:47, 9 September 2013 (UTC)
You're right that the names are unsatisfactory, but sometimes language does unfortunate things like that. This has been discussed before on Wikipedia. We have to accept the names, as the IAU is unlikely to change them. Rothorpe (talk) 00:15, 10 September 2013 (UTC)
The choice of name appears to have been part of a strategy to get Pluto reinstated as a planet "through the back door". So yes, it would seem a bit dishonest. If you dislike it, I suggest you take Brown's advice and use "planetoid" instead. — kwami (talk) 03:10, 10 September 2013 (UTC)

Planetary discriminant of Sedna

I restored because the edit summary for deletion was off the mark: Eris and OR10 etc. are not is Sedna's orbital zone. But I haven't reviewed the citation as for whether there's actually a useful mass estimate of the zone to calculate the discriminant. — kwami (talk) 19:14, 30 December 2013 (UTC)

What is the reason to add Sedna in this list, but not other leading dwarf planet candidates, mainly Quaoar and OR10 which appear to be more massive? Ambi Valent (talk) 23:18, 30 December 2013 (UTC)
Sedna is the largest known body in its region, which makes it analogous to Ceres, Pluto, and Eris. It's obvious the other bodies are not going to make planetary status if their larger neighbors do not, but it's not obvious in the case of Sedna. — kwami (talk) 23:33, 30 December 2013 (UTC)
You're right about Eris and OR10: they overlap, but the period difference is more than an order of magnitude. (Cool - it's there to exclude comets, but now we're looking at comet-Sedna!) The mass estimate, though, is wildly inaccurate, since it doesn't consider any smaller (higher-H) bodies. Also, the estimate of 40 is simply based on the odds (best fit) of their seeing exactly one Sedna amongst similar objects on similar orbits -- the realistic range they give is 15-92 (1σ), so 40 is not even a good lower limit. It also doesn't consider any similar sized bodies that might be in less eccentric orbits (as they mention), hence not detectable by their surveys. The reference is not an estimate of the mass of the zone, nor intended to be. If we're okay to use it as a lower limit (say 15 Sedna-mass), then I recommend "<0.07" rather than just the bare number. Tbayboy (talk) 02:54, 31 December 2013 (UTC)
Sounds good. I was wondering if there was anything salvageable at all. Perhaps "estimated <0.07"? — kwami (talk) 04:27, 31 December 2013 (UTC)
Okay. I made the change. Tbayboy (talk) 04:47, 31 December 2013 (UTC)
But 15 is like realistically a lower limit of Sedna-sized objects. But that means that there must be many more smaller objects and possibly some larger objects. So simply "<0.07" would be accurate. --JorisvS (talk) 21:39, 3 January 2014 (UTC)

New Dwarf Planets

Article should probably be updated re: newly discovered dwarf planets 2012 VP113, 2013 FY27 and 2013 FZ27 — Preceding unsigned comment added by (talk) 03:31, 8 May 2014 (UTC)

Although those three are all quite likely to be dwarf planets, they've yet to be studied well and could turn out to be smaller than expected. Either way, they are not yet recognized as dwarf planets, but they are already listed in the article list of possible dwarf planets. --Patteroast (talk) 07:05, 8 May 2014 (UTC)

Banners at the top of this page

There are two banners at the top of this talk page that talk about content from Dwarf planet candidates having been merged into this article. The second one also says "That page now redirects here.", but in reality it redirects to the list page we also have, list of possible dwarf planets. This is a bit dishonest. Can we do something about it? --JorisvS (talk) 16:23, 30 September 2014 (UTC)

I found something

somewhat objectionable. In Section 3.2, “Characteristics#Size and mass”, the second paragraph, which begins, “When an object is in hydrostatic equilibrium…”, has no inline citations. It is a fairly long paragraph, and having such a long passage without direct citations is undesirable, particularly in what is nominally a Featured Article.--Solomonfromfinland (talk) 03:06, 20 January 2015 (UTC)


"It is estimated that there are hundreds to thousands of dwarf planets in the Solar System. The IAU currently recognizes five: Ceres, Pluto, Haumea, Makemake, and Eris.[11] Brown criticizes this official recognition: "A reasonable person might think that this means that there are five known objects in the solar system which fit the IAU definition of dwarf planet, but this reasonable person would be nowhere close to correct."[12] It is suspected that another hundred or so known objects in the Solar System are dwarf planets.[13] Estimates are that up to 200 dwarf planets may be found when the entire region known as the Kuiper belt is explored, and that the number may exceed 10,000 when objects scattered outside the Kuiper belt are considered.[14] Individual astronomers recognize several of these,[13]" This paragraph should be re-written, consolidating the estimates. (talk) 02:15, 24 January 2014 (UTC)

How would you consolidate them further? They're already consolidated in the first passage you put in bold. — kwami (talk) 02:52, 24 January 2014 (UTC)
I agree it's murky. What does "clear its orbit" mean? Pluto and Earth both have large moons, so why is Earth a planet but Pluto a "dwarf planet"? Do the Trojan asteroids in Jupiter's orbit disqualify Jupiter? (talk) 04:00, 18 February 2014 (UTC)
"Clearing its orbit" means that an object scatters objects that are in similar orbits. Most of those objects are then removed from its neighborhood or impact it, but may also be captured in resonances (of which the trojans are a special case), or be captured as moons. The opposite does not work: An object need not be able to clear its orbit to have moons: There are very small asteroids that are known to have moons. Pluto orbits with oh-so-many Kuiper belt objects, so can't clear its orbit. Jupiter has those trojans locked in 1:1 resonance, so needs to control its orbital zone (and hence can clear its orbit). Neptune controls countless resonant Kuiper belt objects, notably Pluto itself, so same here. Earth also has a trojan. --JorisvS (talk) 07:38, 18 February 2014 (UTC)
Clearing the neighborhood means that the body controls the orbits of everything in its path. The orbits of the Moon and the near-Earth asteroids are completely controlled by Earth. Ditto with Jupiter and the Trojan asteroids. Pluto, on the other hand, does not control the orbits of the Kuiper belt, Neptune does and that makes Neptune the planet. 2601:8:8900:436:7CC1:77A9:4DE3:5A63 (talk) 05:16, 21 February 2014 (UTC)
True, astronomers think there are probably hundreds if not thousands of DPs in our Solar System. However, except for Ceres, they are too far to observe in any detail, so it is hard to see directly what shape they are. Therefore, only Ceres, Pluto, Eris, Haumea and Makemake have been officially declared DPs; Ceres because it is very nearby and we can see directly that it is round; the other four because they are so bright that, even with 100% albedo, they would be so big that there is ~no way they could fail to be round (except Haumea, which is egg-shaped due to rapid rotation). Sedna is almost certainly a DP, but there is ?just enough doubt that it hasn't been officially declared such. We can tell how massive Quaoar and Orcus are, because they each have a moon; they are almost certainly dwarf planets, but they haven't been formally declared such.--Solomonfromfinland (talk) 02:54, 20 January 2015 (UTC)
An sidenote should be placed with this: the size at a (geometric) albedo of 100% does not correspond to a "minimum" size, because geometric albedo can be higher than 100% (e.g. Enceladus at 1.375). It would, however, be exceedingly unlikely that they would not be round. Also, Makemake is (also) noticeably flattened. --JorisvS (talk) 09:56, 20 January 2015 (UTC)
Geometric albedo can be greater than 1? I didn’t know that. Can you give a source? (And by what mechanism can it exceed 1?) If so, the fact that geometric albedo can exceed 1 should be mentioned on one or more relevant Wikipedia articles, possibly including this one. Still, I believe Makemake, Sedna etc. are round. As for Makemake being flattened, that could be due to it spinning (Earth is slightly flattened as a result), or perhaps a telescopic illusion (Makemake is so far away, it is hard to see in any detail; I don’t know how, if at all, a telescope might slightly distort the appearance of such an object).
Btw, it should be “A sidenote”, not “An sidenote”.--Solomonfromfinland (talk) 02:11, 30 January 2015 (UTC)
See Geometric albedo. Tbayboy (talk) 04:58, 30 January 2015 (UTC)
@Solomonfromfinland: I know that, it's just a typo I missed. That it can be higher than 1 is, as Tbayboy points out, discussed in that article. It would be good to remark this more explicitly here (the note "assuming a geometric albedo of ≤1" in the lead was already supposed to imply this to the reader). The only way Makemake would appear flattened to us is because it is flattened, which should be expected with its small rotation period. Because rocky Vesta achieved hydrostatic equilibrium in the past (only to have it disrupted in multiple ways) and icy Phoebe at just over 200 km in diameter also having achieved it only to be battered out of it, I have a hard time imagining many of the larger and not-so-large TNOs as not round. If they likely have thermal histories more like that of Proteus, it becomes easier. Moreover, we know that this roundedness need not imply hydrostatic equilibrium thanks to the round moons of Saturn, most of which are not technically in hydrostatic equilibrium. --JorisvS (talk) 10:37, 31 January 2015 (UTC)
Can you explain the exact difference between roundness (or oblateness, for rapidly-rotating objects like and hydrostatic equilibrium? If Vesta was in hydrostatic equilibrium but it got disrupted, I can see why it wasn’t corrected: Vesta is too small. This implies that Vesta is not truly in hydrostatic equilibrium.
I guess Makemake is flattened after all. How fast does it rotate?--Solomonfromfinland (talk) 08:07, 13 February 2015 (UTC)
Makemake is indeed flattened, which is because it rotates quickly, with a period of only 7.77 h. Vesta attained HE in the past, but a different rotational period froze in and its ellipsoidal shape was disrupted by giant impacts. Now, if it weren't for those impacts Vesta would still be round, but because its rotational period does not match its ellipsoidal dimensions, it would still not be in HE. We have examples of this in the Solar System: All round moons of Saturn except Titan and Rhea are not in HE because their dimensions do not match their rotation periods. This is also true for Iapetus, which is approximately the size of Makemake. So if DP-ness is dependent upon technical HE, not roundness, then Makemake need not be a DP. But then again, so what if its shape froze in at a different rotational period than its current one: It still freezes in for similar-sized objects that just happen to stay rotating at the same period as when their shape froze in, which does not mark an important dividing line in what such objects are, but is just a meaningless technical point. --JorisvS (talk) 12:15, 13 February 2015 (UTC)

"Nearly round"

We need to avoid this wording, even if some dumbed-down sources use it. Haumea is not nearly round, but is a DP, while Vesta *is* nearly round, but is not a DP. Utterly useless as a definition. Sometimes we just have to write beyond a grammar-school level. — kwami (talk) 18:40, 19 February 2015 (UTC)

I would not call Vesta nearly round. In fact I find that Vesta's criteria for inclusion have been overrated from the start. Serendipodous 19:38, 19 February 2015 (UTC)
Agreed, I don't see roundness by any definition in Vesta, not even the old Hubble pictures. From the Feb 12 pictures, Ceres looks pretty rough, not as smooth as the similarly-sized moons -- the main belt is one tough neighbourhood! Tbayboy (talk) 00:38, 20 February 2015 (UTC)
The IAU is the origin of the phrase, in the definition itself, so it's not really "dumbed-down" for sources to use it. "Round" is sometimes used in maths to mean "everywhere convex", which may explain why they used it (reminds me of "metal" in astronomy, which is not the dictionary definition). "Convex" might make a suitable shorthand, but I don't think we could use it, or any other such description, without sources. But I'm happy with the "...H-E..." phrase you used, ugly as it reads. Tbayboy (talk) 00:38, 20 February 2015 (UTC)
That would be okay, then, though we'd want to supply that definition of "round". Still, "nearly round" would mean not-everywhere-convex, which could include Vesta.
More critically, what about a body that is an ellipsoid but not in HE, like Saturn's mid-sized moons (if they weren't satellites)? Would they be DPs, or former DPs? — kwami (talk) 04:51, 11 March 2015 (UTC)

New NEWS today, for future editing

To quote: (CNN)NASA's tractor-trailer sized Dawn spacecraft will snuggle up to Ceres on Friday, getting close enough to be pulled into orbit and to complete the first mission to a dwarf planet. "I'm just delighted that Dawn is now on the doorstep of Ceres," Jim Green, director of NASA's planetary science division said in a news conference on Monday. Ceres was discovered in 1801 (Pluto wasn't found until 1930) and was the first object found in our solar system's main asteroid belt between Mars and Jupiter. ... ... ... [As you all know, right?]

Headline-1: NASA spacecraft nearing mysterious dwarf planet Ceres

QUOTE: "Ceres was demoted to an asteroid because 19th century astronomers couldn't be sure it was round. But it was bumped up to a dwarf planet when that category was created in 2006." -- AstroU (talk) 13:21, 3 March 2015 (UTC) -- PS: FYI for future editing.

CNN is not a RS. And in this case they're wrong. — kwami (talk) 04:52, 11 March 2015 (UTC)

Discovering new dwarf satellite

A group of astronomers of university of Cambridge have discovered 9 new dwarf satellites which orbit the Milky way galaxy. The largest number ever discovered. Read more:

MansourJE (talk) 07:53, 11 March 2015 (UTC)

Those are dwarf galaxies, not dwarf planets, so not relevant to this page. Tbayboy (talk) 12:17, 11 March 2015 (UTC)


'A dwarf planet is an object the size of a planet...' So if Mercury were the size of Ceres it would, having cleared its orbit, still be a planet? Just checking. Rothorpe (talk) 17:37, 7 December 2014 (UTC)

Yes. But that's unlikely, since a low-mass object like Ceres is not gravitationally strong enough to clear its neighbourhood completely. Serendipodous 18:11, 7 December 2014 (UTC)
Right, thanks. Rothorpe (talk) 18:36, 7 December 2014 (UTC)
It would have a Stern–Levison parameter of less than 1 (Λ~Μ2), and so would not clear its orbit over the age of the universe, let alone during its existence. However, if one would suddenly reduce Mercury's mass to that of Ceres, it would still appear to have cleared its neighborhood, and therefore still appear a planet. But that would be artificial. --JorisvS (talk) 18:47, 7 December 2014 (UTC)
Yes, that's what I was wondering about. Thanks. Rothorpe (talk) 20:14, 7 December 2014 (UTC)
The definition points up the fact that it is an unsatisfactory term, which I suppose is good. ('Planetoid' would perhaps have been a little better, but it still has the connotation of size. Which reminds me of 'asteroids', 'little stars', a much worse misnomer, long accepted.) Rothorpe (talk) 16:45, 8 December 2014 (UTC)
Don't "planetoid" and "asteroid" mean "like a planet/star", rather than "little planet/star"? Iapetus (talk) 10:19, 12 March 2015 (UTC)


There has been a change by an IP removing Sedna, which has been reverted. However, I agree with the removal of Sedna as of now - as has been stated, it isn't on the IAU's list and while it is "accepted by many" (as in the reasoning behind the revert), so is e.g. Quaoar. I cannot see the reasoning behind including Sedna and at the same time excluding the other "mostly certain" candidates. I would be more than happy to include them all, but as it stands, the IAU is the authority we are referring to (as they started the "dwarf planet" category) and they do not include Sedna - yet. --Ulkomaalainen (talk) 02:46, 20 March 2015 (UTC)

Sedna is there as a representative of that region of the solar system. Whether or not it is a dwarf planet, it's the largest known object in a distinct dynamic class. The other major dynamic classes with known candidates have representatives amongst the IAU DPs. Tbayboy (talk) 03:21, 20 March 2015 (UTC)
Also, the IAU isn't much of an authority. They've declared certain criteria for which commission gets to name which body. They aren't actually in the business of deciding whether s.t. is a DP. Since no other bodies meet their dual-commission criteria, they aren't bothering with DPs any more. The IAU five are a bureaucratic set, not an astronomical one. For the life of me I can't understand why we're using them an the authority, when they plainly aren't trying to be. — kwami (talk) 03:55, 20 March 2015 (UTC)
Basically because including Sedna and excluding others would need another authority. Otherwise we would end up using WP:OR. And the dismissal of the question of "whether or not it is a dwarf planet" seems strange on an article about dwarf planets. There are other articles here about candidates, trans neptunian objects, asteroids and so on, and even here they can be mentioned. But adding Sedna to a table with the designated dps is in my opinion confusing the reader unless we find an authority which includes Sedna (and excludes Quaoar, Orcus, Varuna etc.). --Ulkomaalainen (talk) 11:36, 20 March 2015 (UTC)
Not so much. It is not meant as a exhaustive list of μs or Λs. Only the most massive objects in a region need to be considered. If they fail, all others automatically fail, too. Quaoar, Orcus, Varuna etc. all orbit squarely in the Kuiper belt, so if Makemake fails (it does), then these do, too. Their μs are lower than that of Makemake. No point in including them. --JorisvS (talk) 12:34, 20 March 2015 (UTC)
Since we are talking DPs, not planets, it's not so much about "failing planetary criteria", but about what makes Sedna included in this list which would be understandable. In an article about DPs, this list as of now includes (a) the eight planets, (b) the five Dwarf Planets as chosen/accepted by the IAU, (c) Sedna. And this kind of grouping fails to be explained or sourced to a credible source. It is not about the criteria being technically wrong - I am not enough of an expert to discuss this - but about this sole inclusion seeming like OR to me. The source quoted for the table does not include Sedna (nor Makemake or Haumea for that matter) so it cannot justify this inclusion. If this were a non exhaustive list of "some celestial bodies", it should say so and make clear criteria for inclusion and exclusion. But as it stands it seems like a maybe very useful list, but made by Wikipedia itself which would constitute OR and presented in a way that furthers the suggestion that this set of six (Ceris, Eris, Makemake, Haumea, Pluto, Sedna) has a common ground which is not explained (my first reaction when scrolling across this table was "Oh, the IAU included Sedna now?" - which of course was easily countered by the lead paragraph. Long story short, I still think this list does not explain its criteria for inclusion, especially its deviation by one entry if compared with the easily spotted set up of "planets and IAU recognized dwarf planets" and at the same time does not correctly reference the quoted source. --Ulkomaalainen (talk) 21:36, 20 March 2015 (UTC)
I agree that the rationale for inclusion should be explained (better). These values remain accurate even if Sedna would turn out not to be a DP, they just wouldn't have any relevance. Maybe we could prune the IAU-5 down, because I think what I said above may apply to the Pluto–Makemake–Haumea set, but that should be analyzed better first. --JorisvS (talk) 23:13, 20 March 2015 (UTC)
Note that this is in the section "Orbital dominance", which is a criterium for planets. The table is there to show how DPs (both official and candidate) are not planets, as explained in the section text, and to illustrate the huge gap in dominance. JorisvS is correct that Makemake and Haumea aren't really necessary, since Pluto and Eris together cover the TN belt and are clearly larger than anything else. Also note that Pluto's µ is incorrect in the source, since Soter forgot to include Neptune in Pluto's orbital zone! Tbayboy (talk) 00:24, 21 March 2015 (UTC)
Resonances are a tricky thing with these values. Even though Jupiter and Neptune are by far the most massive in their orbital zone (and the dominant one; else there couldn't be also those minor planets in resonance with them), the resonant objects are not going to be scattered away by them. Rather, it is a special case of clearing their orbital zone. Including these objects' mass in the calculation can be misleading as can be understood from the hypothetical case of two co-orbital planets of roughly equal mass in an exchange orbit (say like that of Saturn's Janus and Epimetheus): A naive calculation of their planetary discriminant leads to a value on the order of ~1, which would lead to the false conclusion that these are not planets. Similarly, two (massive) planets (ice giants or even gas giants) could be in a non-co-orbital resonant configuration on crossing orbits, yet it would be ridiculous that this would disqualify them from being planets. The latter case is not unlike that of Neptune and Pluto, so I don't think it is actually correct to include Neptune's mass in the calculation of Pluto's planetary discriminant. --JorisvS (talk) 00:52, 21 March 2015 (UTC)
You're right. And Soter explicitly excludes resonant objects in his definition. I always think of an object in resonance as a kind of satellite, and that in turn as a back-handed accretion. Would Pluto and Orcus be considered resonant with each other? Their orbits should be synchronised, but obviously not because of their own gravity. Tbayboy (talk) 14:24, 21 March 2015 (UTC)
That's tricky. Beyond some 10–20 million years (its Lyapunov time), Pluto's orbit is unpredictable (nevertheless stable), and something similar should be the case for Orcus. So although they currently stay very far away from each other, wouldn't this mean they may come to orbit much closer to each other in the future/past, meaning one would scatter the other if they had sufficient mass? --JorisvS (talk) 16:46, 21 March 2015 (UTC)
They could also be at different points along their orbit (e.g., one at perihelion and one at aphelion) so that even if they're in the same orbit they might never get close. I wonder how much "slippage" there is; i.e., breaking the 3:2 resonance then getting pulled back into it, but at a different point in the orbit. Or does that manifest as a different argument of perihelion? Anyway, I don't think resonance is transitive, so Pluto and Orcus would count towards each others orbital zone material. Tbayboy (talk) 14:24, 22 March 2015 (UTC)
Could be, but not necessarily so. Don't their orbits librate/circulate? And what about the perturbations from the other planets, and even other large minor planets, slowly reorienting their orbits? --JorisvS (talk) 14:37, 22 March 2015 (UTC)
I think a note should be added to the table's caption that the table includes 8 planets, 5 dwarf planets and Sedna as a representative of Ooort cloud population. Ruslik_Zero 20:01, 21 March 2015 (UTC)
Agreed, but if a correct note (i.e. that the most massive object in an orbital region is shown, because these values are necessarily lower for all other objects) is added, is there still a point in keeping Makemake and Haumea in there? --JorisvS (talk) 20:29, 21 March 2015 (UTC)
I took a try at it. Lightened the purple to be printer friendly. Commented out Haumea and Makemake, so we don't lose the numbers. It's too much text to put above the table with the caption. Tbayboy (talk) 15:12, 22 March 2015 (UTC)
I like the version a lot. Thanks for the change and the constructive and polite discussion. --Ulkomaalainen (talk) 03:22, 23 March 2015 (UTC)

H values in the tables

Since it is used as a criteria for the recognized dps, the H value should be added to the physical characteristics tables. Nergaal (talk) 06:17, 30 May 2015 (UTC)

Done. Tbayboy (talk) 18:45, 30 May 2015 (UTC)


"On March 6, 2015, the Dawn spacecraft began to orbit Ceres, becoming the first spacecraft to orbit a dwarf planet. Later in 2015, the New Horizons is expected to fly by Pluto.

After Ceres, the next-most-massive body in the asteroid belt, Vesta, might also be classified as a dwarf planet, as its shape appears to deviate from hydrostatic equilibrium mainly because of massive impacts that occurred after it solidified. The definition of dwarf planet does not address this issue. Data from the Dawn probe, which orbited Vesta in 2011–2012, may help clarify matters."

I'm assuming there is other information that is outdated with the new Pluto measurements from New Horizons. Jameswrjobe53 (talk) 02:19, 15 July 2015 (UTC)

I removed the Vesta comment. Pluto's size was correct, just an error in the error bar. I haven't looked into the derived numbers (density, albedo, gravity, etc.). Tbayboy (talk) 02:38, 15 July 2015 (UTC)
And I fixed the tense in the other statement. I also removed the {{outdated|date=July 2015}} hatnote. It's a complete overkill, especially since this is a featured article and there is already a hatnote {{Current related||New Horizons{{!}}''New Horizons''. Rfassbind -talk 09:58, 15 July 2015 (UTC)
    • ^ Mike Brown, 2012. How I Killed Pluto and Why It Had It Coming