Talk:Kuiper belt

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Pronunciation of Kuiper[edit]

A website about the Dutch pronunciation of names is linked as a source reference for the pronunciation of "Kuiper". Nevertheless, the English pronunciation is used in this article. In Dutch, the "ui" digraph is IPA: [œy], therefore I believe that "Kuiper" should be IPA: [ˈkœypər]. – Ilse@ 13:13, 15 July 2008 (UTC)

Well, the Dutch page has a recording of someone pronouncing "Kuiper," and he pronounces it "Kyper". Scroll down to where it says "scientists". Serendipodous 12:23, 17 July 2008 (UTC)
The IPA transcription is original research. No IPA is given on the linked site. Besides, the English name Cowper is cognate with Kuiper. I don't think there's any greater authority.--Rfsmit (talk) 22:01, 10 February 2010 (UTC)
I have always heard it pronouned as "Kaiper", which the article appears to be consistent with. -RadicalOneContact MeChase My Tail 22:04, 10 February 2010 (UTC)
Pronunciation discussion copied from its original location

Verbatim, below. Iridia (talk) 01:11, 21 April 2009 (UTC)

I've followed your advice and read, but the only discussion I see regarding the pronunciation of Kuiper is, in which Ilse@ confirms my correction, and Serendipodous's reply that the mentioned website has Kuiper pronounced as Kyper is wrong, it is clearly pronounced [œy], which is correct, see [œy] being not a native vowel in English may have caused this confusion. —Preceding unsigned comment added by Upquark2 (talkcontribs) 10:32, 20 April 2009 (UTC)

You claimed by your IPA link that it was the English pronunciation, which by your own admission is impossible. The Dutch pronunciation is provided in Kuiper's bio. kwami (talk) 10:46, 20 April 2009 (UTC)
OK, now I'm confused. Do you mean that in English, non-English names should be pronounced as if they were English? So Kuiper should be pronounced /ˈkaɪpər/ while it's actually a Dutch name? Confusing... but if it's the case, thanks for having learned something new. Upquark2 (talk) 10:57, 20 April 2009 (UTC)
Sigh. Please check that Dutch link again. If you go down to where it says "scientists", Gerard Kuiper's name is listed next to an audio file. Listen to the audio file, and the voice clearly says, "kyper." Presumably, Kuiper changed the pronunciation of his own name when he went to the States and, since he was in the States when he wrote his paper, it follows that that was the pronunciation he used at that time. Ergo, it is pronounced "Kyper." Serendipodous 11:14, 20 April 2009 (UTC)
Sorry, but the voice (native Dutch speaker) really says [œy], like 'ui' should be pronounced in Dutch. I agree it's close to 'Kyper', though. Upquark2 (talk) 11:41, 20 April 2009 (UTC)
Even if that weren't the case, his name has become fully anglicized by English-speaking astronomers, and we would still use their pronunciation. kwami (talk) 11:35, 20 April 2009 (UTC)
Reasonable argument, I can live with that. Upquark2 (talk) 11:41, 20 April 2009 (UTC)
The problem is that people, when told not to pronounce it "Kyper", tend to pronounce it "Koyper", as an analogy to "Huygens", so it's best, for English speakers anyway, to say "Kyper." Serendipodous 10:04, 24 April 2009 (UTC)

Fair enough that the name got Anglicized and therefore now rhymes with "viper" (as mentioned in the article), whereas in fact it does NOT rhyme with viper. I would suggest to at least add the original Dutch pronunciation to it. Something like this: (pronounced in English /ˈkaɪpər/, rhyming with "viper" and originally in Dutch: /'kœypər/). For Dutch people there is a big difference between aɪ and œy. Baske77 (talk) 21:18, 31 January 2010 (UTC)

Is there some way to indicate the difference to English speakers? Because I have listened to that word hundreds of times and I still can't hear it. Serendipodous 23:04, 31 January 2010 (UTC)
I don't think there is an easy way to indicate to native English speaking people how the sound is significantly different for Dutch people. As the English language does not have the sound it is hard to hear it, I think. In favour of my suggestion I would like to point you all to the article of Christiaan Huygens (also a Dutch name, with the same sound in it) Christiaan_Huygens Where indeed both the English and the Dutch pronunciation are mentioned. I think a similar construction would be good for the Kuiper Belt article. Baske77 (talk) 12:30, 2 February 2010 (UTC)
The Huygens article has "hy-gens" for the English and "hoy-gens" for the Dutch, which sound very different to English ears ("by"/"boy"). The Dutch pronunciation site I linked to sounds almost exactly like "ky-per"Serendipodous 14:01, 2 February 2010 (UTC)
Doesn't matter. That's Howgens, this is Cowper (heh heh). Your English ears aren't attuned to Dutch pronunciation, the same way Chinese ears have great difficulty distinguishing L and R; the same way my Northern English ears have great difficulty distinguishing Southern English A and I.--Rfsmit (talk) 22:12, 10 February 2010 (UTC)
My problem with this is that a lot of English speakers think that Kuiper should be pronounced like "koy-per", which doesn't appear to be the case. If I just include the recommended Dutch pronunciation without some kind of example, people might come away assuming it should be pronounced "koy-per". Serendipodous 16:25, 11 February 2010 (UTC)
Indeed, since the word is fully anglicised, the Dutch pronunciation is irrelevant in this article which is about the Kuiper Belt. People can go to the article on Kuiper, the man if they want to know how to pronounce the name of the person from whom the Belt's name comes. Ashmoo (talk) 23:37, 23 March 2010 (UTC)
Just a quick thanks for having the pronunciation in this article. I've always wondered and finally followed-up on my curiosity. – Kerαunoςcopiagalaxies 22:05, 26 May 2010 (UTC)
I don't want to argue here about the anglicised pronunciation of Kuiper, I only want to give some final information about the Dutch pronunciation. I'm Dutch, and I've met many people with English as their native tongue. Among them some who speak nearly accentless Dutch, but they allways 'give themselves away' in their pronunciation of the Dutch 'ui'. They simply can't get it done. It's not oy as in boy, neither y as in by. For a Dutch man's ears, these two suggestions don't even come close to what it should be. To be complete: uy is an old spelling of ui, and it's pronounced exactly the same way in modern Dutch (we can't be sure of the 17th century pronunciation).Dunglisher (talk) 20:47, 30 April 2012 (UTC)
From a South African English point of view Afrikaans /ui/ is perceived to be the rounded form of /ei/ or /y/ and therefore if speaking English and not trying to exactly match the Afrikaans pronunciation (as the /ui/ sound is not native in English) that is what it would be pronounced like. Kuiper would be pronounced as "caper" (the little green pickled thing). Now I'm not sure if Dutch /ui/ is pronounced the same as Afrikaans, but I suspect it is.
At school we were always taught to pronounce the sound in this way; if trying to say "Kuiper", say English "caper" but keeping the tongue firmly on the bottom of the mouth for the "A" sound, with lips rounded and slightly pouted as if to to kiss someone! — Preceding unsigned comment added by (talk) 12:50, 13 July 2015 (UTC)
As a native Dutch speaker living in the Netherlands, I just wanted to say I think this is the best description I have ever seen, of how to pronounce the "ui" sound in Dutch. I had to try it to believe it, and yes, I think you nailed it. ;) As Dutch people we are aware how tricky our "double vowels" (au/ou, oe, eu, ui, ei/ij) are to pronounce for foreigners, and frankly, a lot of Dutch people do a sloppy job themselves on a daily basis. Especially "ui" "eu" and "ei/ij" may be tricky to learn, and tricky to distinguish between them. They are different though, and "ui" is also different from the "y" (like in "hyper"). They may sound so simmilar to a non-native Dutch speaker, that people may THINK they are hearing "y" even in an audio clip demonstrating the pronunciation (as evidenced by a few reactions here in this discussion), while a native Dutch speaker will say, no that's clearly an "ui" you are hearing. Greetings, RagingR2 (talk) 12:03, 4 February 2016 (UTC)


Some notes on origins and the Nice model

The instability has many variations, in those examined in the 2008 paper Neptune is scattered outward into a high eccentricity orbit which is then damped by dynamical friction and migrates out toward its current orbit. While Neptune's orbit is eccentric its mean motion resonances overlap and orbits in the region between its 3/2 and 2/1 resonance are chaotic, during this phase low inclination objects are shifted outward forming the cold belt. Later as Neptune is migrating outward the hot belt forms as some of the scattered objects are decoupled from Neptune through secular and mean motion resonances. In addition to the eccentricities in this variation not matching observation, the loosely bound binaries in the cold belt would be split if they encountered Neptune leading to suggestions that the cold disk formed in place, and the hot belt doesn't include enough higher inclination objects.

There were some later (rather technical) papers that examined what orbits Neptune could have which preserved a cold belt while populating a hot belt, these used lower eccentricities than the 2008 paper. And another that looked for ways of leaving the outer part of the cold belt with higher eccentricities.

Then there is the five planet version where in some cases Neptune migrates outward several AU before the planetary encounters begin. The hot belt is created in much of the same manner as in the 2008 paper, except part of this occurs before the planetary encounters, and the inclination distribution can be matched with the right combination of timescale and migration distance, Objects captured in the 2/1 resonance during the first part of Neptune's migration are left behind as a local concentration at 44 AU in the cold belt when Neptune semi-major axis jumps outward as it encounters the extra planet sometime before that is ejected. Later the eccentricity distribution of the cold belt can be truncated by slow resonance sweeping.

I'm thinking of adding, well seeing how long it turned out, some of this to the origin section. Probably the point about the cold belt being formed at its current locations because of the loose binaries, the inclination distribution mismatch in the 2008 paper, and something about the five planet version.

But, this having been rated a feature article, I would like other opinions first.Agmartin (talk) 18:24, 1 February 2016 (UTC)

I think this would be good material to add. This article is somewhat dated and in need of refresh to be brought up to speed. -- Kheider (talk) 20:26, 1 February 2016 (UTC)
Same here. Serendipodous 12:28, 13 February 2016 (UTC)
I've rewritten parts and added some new material from a recent five planet version of the Nice model with some comparison between the two versions.

@Agmartin:, just going through your additions to the article (great addition on the whole) and am unclear as to the definition of the "hot disk"; I'm assuming that is the same as the dynamically hot classical Kuiper belt, but am not certain. Serendipodous 16:27, 27 February 2016 (UTC)

That's what I meant, I was trying to abbreviate since my additions were getting rather long. Given that the current division between the hot classical belt and the scattered disk at a semi-major axis of 50 AU appears arbitrary, I think it could also be used to refer to both, though using it that way may need to await a paper that specifically spells out that they formed via the same process. Agmartin (talk) 17:47, 27 February 2016 (UTC)
Perhaps using hot belt instead might have have been better. Agmartin (talk) 17:51, 27 February 2016 (UTC)
I've done some changings. Serendipodous 18:04, 27 February 2016 (UTC)
Good idea about relocating sections. I switched the 'recent modifications' link to Hypothetical_fifth_giant_planet. I've been pondering moving that article to five planet Nice model since that is what it is describing. What do you think? Agmartin (talk) 19:46, 27 February 2016 (UTC)

Oort Cloud a thousand times more distant? I think not...[edit]

The article reads "The Kuiper belt should not be confused with the theorized Oort cloud, which is a thousand times more distant..." That depends on how you look at it...

Kuiper Belt: from 30 to 50 AU from the Sun. Oort Cloud: beginning at somewhere between 2000 and 5000 AU, and ending somewhere between 50.000 and 200.000 AU. (Note that the outer limit carries the greatest level of uncertainty.)

So depending on these numbers, you could say:

  • the beginning of the Oort Cloud is somewhere between 67 and 167 times as distant as the beginning of the Kuiper Belt
  • the center of the Oort Cloud is somewhere between 26.000 and 102.500 AU, so that's somwehere between 650 and 2562.5 times as distant as the center of the Kuiper Belt.
  • the outer limit of the Oort Cloud is somewhere between 1000 and 4000 times as distant as the outer limiet of the Kuiper Belt.

As you can see, these numbers vary greatly, and it depends strongly on which way you look at it, which number is the most appropriate. Personally, I feel when describing how distant something is, it makes more sense to talk about where it begins, or MAYBE where the center is, but not where it ends. You don't say "Europe is XXXX kilometers away", and then refer to the geographical center of Europe or where Europe ends. No, you will refer to whatever European border you will reach first from your location. You don't say "that group of people is standing XXX meters away from me", and then refer to where the center of the group is. No, you will measure it according to where the first people from your position are standing. In any case: these numbers are also based on data (for the Oort Cloud specifically) that is still pretty uncertain.

So all things considered I think it's at the very least a false suggestion of accuracy, and in the worst case an exaggeration to say that the Oort Cloud is 1000 times as distant as the Kuiper Belt. I think a more appropriate description would be "2 or 3 orders of magnitude more distant". That way you leave it open whether it's in the 100's or in the 1000's; which is appropriate since the specific details of the Oort Cloud still carry a great level of uncertainty.

(P.S. And even then it's pretty generous, because if the Oort Cloud indeed will prove to begin at 2000 AU, then the beginning is "only" 67 times as distant as the Kuiper Belt's beginning, so that's not even in the 100's.)

Greetings, RagingR2 (talk) 00:35, 5 February 2016 (UTC)


Looking at the citations in this section it doesn't appear to have been updated recently. I have found this review article from 2012 discussing the composition and the surfaces of the Kuiper belt objects. The Compositions of Kuiper Belt Objects And this more recent paper Agmartin (talk) 22:26, 1 March 2016 (UTC)

Some things from the first source that could be added to this section.

The binary objects with known masses determined from their orbits and diameters determined by measuring albedo using thermal emissions have a variety of densities. Some small objects have densities significantly below that of ice indicating that they are very porous and contains little rock. The largest objects are more dense indicating that they contain a significant fraction of rock. The varying densities may be due to the locations where they formed with the mix of materials varying with distance from the sun, or be due to loss of ice when objects merged to form the largest bodies.

The albedos of the moderate to large objects increase with diameter.

The spectra of the largest bodies indicate the presence of methane, in some cases dissolved in nitrogen, carbon monoxide is also expected to be present. Their presence on the surface of only the largest objects may be due to their retaining a thin atmosphere. The methane in processed by radiation into ethane and heavier hydrocarbons causing surfaces to darken and redden. Crystalline ice has been detected on surfaces of moderate to large objects, this may be due to cryovolcanism aided by the depression of the melting point of water due the ammonia.

The colors of smaller objects are either dark and neutral or brighter and very red. Binaries have similar colors indicating that both components formed in similar locations or that they binaries formed in their original collapse. One hypothesis for the differing colors is that the red objects formed far enough from the sun to retain methanol. The cold classicals are all red, other dynamical classes contain a mix of colors. Agmartin (talk) 22:45, 3 March 2016 (UTC)

I'll get going on this soon. Serendipodous 22:52, 3 March 2016 (UTC)


I've replaced the histogram with an up to date one split by inclinations above and below 5 degrees. That file didn't include Neptune trojans. The link to the file with those included is here

Histogram of Kuiper belt objects with inclinations above and below five degrees. Includes Neptune trojans.

(click on edit to see the link) if that is the preferred version. Agmartin (talk) 21:54, 4 May 2016 (UTC)

What is the "kernel"? I don't think that's defined in the text. Serendipodous 21:35, 4 May 2016 (UTC)
I mentioned a concentration of objects left behind when Neptune jumped outward in the origin section. I hadn't noticed that it wasn't discussed previously. I guess I'll need to add that. Agmartin (talk) 21:54, 4 May 2016 (UTC)

size distribution[edit]

I believe the illustration and text related to the size distribution power law are wrong. If N represents the number of objects with diameters greater than D then if q=4 the number of objects of diameter 2D should be 1/16 of those of diameter D. The total number of objects larger than 2D should be 1/8 of those larger than D. If I'm misunderstanding would someone point out what I'm missing. Agmartin (talk) 20:25, 11 August 2016 (UTC)