Talk:Scattered disc

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Featured article Scattered disc is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Wikipedia community. Even so, if you can update or improve it, please do so.
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FA status![edit]

Congratulations to every one who contributed to making this article FA along with 16 other solar system topics. I have been wanting to see this article become FA for a while now... Celtic Muffin&Co. (talk) 20:04, 11 September 2008 (UTC)

Subdivisions of trans-Neptunian space[edit]

The caption in the illustration of scattered-vs-resonant-vs-classical TNOs defines KBO/Plutoids as 5:2 resonance, the article defines them as 3:2. I assume the caption is just a typo, but am not sure enough to risk changing it. -- PaulxSA (talk) 00:21, 17 October 2008 (UTC)

Thanks for pointing this out. It is correct, but I can see why someone could be mislead by the wording. I linked 5:2 resonant to Resonant trans-Neptunian object. All plutinos are in a 3:2 resonance, but there are many other resonances. -- Kheider (talk) 01:12, 17 October 2008 (UTC)

Featured![edit]

Congratulations to election to Featured article! ... said: Rursus (mbork³) 07:27, 23 October 2009 (UTC)

is the SD in the KB?[edit]

Over on the KB talk page,* s.o. claiming to be Mike Brown said that the SD is part of the KB, and that our claim that Eris is not a KBO is bizarre. I've checked a few articles, and though none say it explicitly, they do seem to take it as understood that this is the case. (Though not Sedna, which several say lies outside the KB.) What were our reasons for excluding the SD from the KB? Can we justify it? Considering this is a FA, IMO we should settle this quickly. — kwami (talk) 16:53, 10 September 2011 (UTC)

The issue is the Minor Planet Center, which classifies scattered objects and "Trans-Neptunian objects" separately. Given that there is no consensus among astronomers as to what to define as the KB, as can be seen here, the best thing to do is to follow, as best as possible, the Minor Planet Center's lead, as was decided here. Serendipodous 17:35, 10 September 2011 (UTC)
Thanks for the link! — kwami (talk) 22:40, 10 September 2011 (UTC)
IMO trying to read anything explicit into the MPC categories is OR, unless they actually explain what they're doing an why. People often make 'other' lists, and that's all the TNO list might be, considering that everyone agrees that the SDOs are TNOs. The MPC list should therefore not be used as evidence for anything.
At User:AstroMark/wip/KB definitions I added a ref explaining the two uses of the phrase KB. That does seem to be what's going on: even within a single volume, authors sometimes switch back and forth between the SD being a subset of the KB to it being a distinct region. There would thus seem to be no one correct answer, and we should do whatever is convenient for us, unless usage converges on one def or the other. I think if we add "(classical)" in front of KB/KBO when we're excluding the SD, that should make it clear what we're doing.
I've added a note to several articles, explaining that when we say KB, we mean the classical belt. The most confusing aspect of this may be the classical Kuiper belt objects, which are not generally members of the classical Kuiper belt. — kwami (talk) 23:09, 10 September 2011 (UTC)
Actually, when we make the "Kuiper belt" and "scattered disc" separate we mean both the classical belt and the resonances, so employing the term "classical belt" is insufficient. It's one thing to say that Pluto is the largest object in the Kuiper belt, but if we start saying Pluto is a classical Kuiper belt object, we're screwed. Serendipodous 06:12, 11 September 2011 (UTC)
Resonances occur both in the classical Kuiper belt and in the scattered disk.
As for reverting my sources, perhaps you'd like to provide something other than your say-so. I never said Pluto was a classical KBO. I said it was in the classical KB. As confusing as that may be, the two phrases do not seem to be synonymous. At least, not according to the source I provided. Perhaps you have better sources, and a clearer term for [KB less SD]? — kwami (talk) 06:37, 11 September 2011 (UTC)
I actually have the source to hand. I checked what it said. It said that it used the term "classical kuiper belt" to identify the "stable regions". That is remarkably vague and suggests that the authors misread the meaning the term. I have provided six references that define what the classical kuiper belt is. Classical Kuiper belt objects are very specific. DO you want me to email these people and ask them? Would that settle it? Serendipodous 06:44, 11 September 2011 (UTC)
I've checked the four of those six sources I have access to, and no, they do not define what the classical belt is. They define what a classical KBO is. Not necessarily the same thing. They include the SD in the KB, as it seems most sources do: there are resonant, classical, and scattered populations of KBOs. An email might be worthwhile. If one includes the SD in the KB, what term is used for the non-scattered population? We could just say Pluto is the largest resonant KBO, but it's also larger than any classical KBO. Another possibility would be to simply merge the SD back into the KB, since our reason for separating it, following the example of the MPC, may well be spurious. (SDOs are obviously TNOs, so the MPC is simply wrong unless one takes "TNOs" to mean "other TNOs", and AFAIK the MPC has not said.) — kwami (talk) 06:55, 11 September 2011 (UTC)

The problem, as I understand it, is that not all scattered objects are purely cis-Neptunian or trans-Neptunian. Some are both. So the MPC's decision to separate them this way makes a certain kind of sense. Serendipodous 07:21, 11 September 2011 (UTC)

Oh, I agree. But it doesn't follow that they're promoting the exclusion of scattered bodies from the Kuiper belt. Most of the sources I've seen, including (I think) most of the ones you've provided, speak of "scattered KBOs" or something similar. Yes, the boundary between those and centaurs is fuzzy, just as the boundary for what one considers an asteroid or a comet is fuzzy. So while it makes sense to list them with centaurs, I think it's OR to draw any further inferences from that. If the majority of sources followed that pattern, it wouldn't matter, but it seems that the majority of sources count them instead as KBOs. Doesn't really matter much, as it pretty much just affects the organization of our articles, until we start saying "Pluto is the largest KBO", as if that were undisputed, when many of our sources would say Pluto's the second largest. I wonder if any of this is planet envy? ('Okay, Pluto may not be a planet, but it's the king of the Kuiper belt!') — kwami (talk) 07:37, 11 September 2011 (UTC)

For the record, here are 172 astronomical articles which use the term "classical belt". Serendipodous 11:48, 11 September 2011 (UTC)

According to the review of Morbidelli (see also [1]) "The trans-Neptunian population is “traditionally” subdivided in two sub-populations: the scattered disk and the Kuiper belt.". Ruslik_Zero 16:47, 11 September 2011 (UTC)

Odd to call anything 'traditional' when the categories are only a few years old. — kwami (talk) 23:52, 11 September 2011 (UTC)
Okay, from the first page of results in Serendipodous' search, we have:
1 [particle physics]
2 Allen: ESD in KB
3 Gomes: CKB between 2:3 and 1:2 res (40-48AU)
SD beyond 1:2 (ad hoc), not clear if in KB
4 Morbidelli: CKB = non-res 40-48AU
not clear if SD in KB
5 Trujillo: scattered KBOs
6 Chiang: scattered KBOs
7 Allen: KB incl. SDOs
8 Levison: ESD beyond 1:2, part of KB
Sedna not in ESD/detached, but a new pop.
9 Gladman: SD != KB
SD not beyond CKB, only beyond Neptune
10 Morbidelli: SD != KB; but SD may also inside KB
So a slight majority count the SD as in the KB, but whereas we say that the SD is beyond the KB, the sources here do not agree. The KB and SD overlap. An exception is Gomes, who proposes we take the SD to beyond the KB; Gladman notes the SD is not well defined. — kwami (talk) 00:31, 12 September 2011 (UTC)
This is not a question of majority. Morbidelli 2008 is a secondary source, which should have precedence over all other (primary) sources. Ruslik_Zero 12:17, 12 September 2011 (UTC)
You mean 2003, I presume.
Jewitt (2000), in Protostars and planets IV, is also a 2ary source, and states that the resonant, classical, and scattered objects are three populations of the KB.
So is Kavelaars (2008) in The solar system beyond Neptune, which speaks of the "scattered" pop of the KB.
2ary sources go both ways too. — kwami (talk) 20:16, 12 September 2011 (UTC)
I meant Morbidelli 2008. Another review, which states that SD is not part of KB, is here. As to your examples, the paper of Jewitt from 2000 is too old.
In addition, from a geometrical point of view it is misleading to call a nearly spherical (somewhat flattened) cloud of objects (SD) a "belt". Belt means something that has sharp outer and inner boundaries and is flat in the vertical direction. Kuiper belt is flat and has sharp boundaries while SD not. Ruslik_Zero 18:57, 13 September 2011 (UTC)
These are all new terms, and still poorly defined. Or at least, they may have explicit definitions which disagree with each other. I'm no judge of the lit as to which is best for our purposes, but I think we do need to keep in mind that many of our sources do not use our definitions, and we need to be up-front about that with our readers. Hopefully the definitions will settle down, but I don't think that's happened yet, and when it does, it may not settle on the usage we've chosen.
I agree that "belt" is a bit odd for the SD, but then "disc" is even more odd, isn't it? A disk is flatter than a belt! Belts tend to have a substantial vertical dimension while discs do not. Personally I would use scattered (TN) objects and leave "disc" out of it for that reason. (Yes, I know SD is common usage, I'm just musing.)
There's also the problem of us saying the SD picks up where the KB leaves off, whereas they actually overlap. — kwami (talk) 01:19, 14 September 2011 (UTC)
Nobody has disputed that they overlap. They are defined as dynamically distinct population of objects occupying the same space. Ruslik_Zero 12:04, 14 September 2011 (UTC)
The articles dispute that. In several places we say that the SD lies outside the KB, that it is further away than the KB, that there's the KB and then beyond that the SD, etc. True on average, perhaps, but incorrect as a general statement. — kwami (talk) 23:31, 14 September 2011 (UTC)
This overlap is why I have not commented as of yet. Many small solar system bodies fall into multiple categories. Myself I generally check the MPC centaur/SDO list and then check the DES evaluation. -- Kheider (talk) 14:32, 14 September 2011 (UTC)