Talk:Clearing the neighbourhood/Archive 1

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(UTC)Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's. (AP)

But what about Neptune? Should not it be disqualified as well? ST47 20:59, 24 August 2006 (UTC)

Was that TIC? •Jim62sch• 21:02, 24 August 2006 (UTC)

Pluto's orbit only overlaps Neptune's in a 2 dimensional map. In 3d space it never does. I think Pluto gets gravitationally dominated by Neptune in it's 2:3 resonance. I think the confusion is coming up by the terminology. We think of "clearing the neighbourhood" like we think of sweeping the porch. All of the major TBOs have "cleared their neighbourhood", their orbit, of all the smaller trash. It's just in a weird sorta way, they don't directly and independantly orbit the sun. They aren't satellites of Neptune, they aren't captured...but satellites of the Sun with Neptune greatly influencing them. There is a lot more empty space between the KBOs and Earth vs. Venus. However Earth doesn't alter Venus' orbit. It you moved Earth all the way out to Pluto's orbit, it is still not massive enough to free itself from Neptune's influence. The definition of a planet has less to do with the

This article is a serious misunderstanding of the term. I don't even know where to begin. It probably doesn't even belong here. I wish people would at least make an attempt to read the primary sources before creating stuff.Derek Balsam 21:05, 24 August 2006 (UTC)

The term means to clear all objects from an orbit, either by taking it as a moon, colliding with it, or slingshotting it out of the orbit.

It properly refers to the history and end-state of the dynamic process of accretion over time from the original planetary disk.

This definition is questioned by the fact that

Trans-Neptunian objects such as Pluto

.

Neptune's orbit does not "overlap" with Pluto's at any point. This is well known, not merely "possible".Derek Balsam 21:11, 24 August 2006 (UTC)

I wiped this and replaced it with a newer stub; it's still wrong (because I'm not entirely clear on this myself - slept through too many lectures) but it's a lot closer to right. Isn't there a better term for this, anyway? "Orbital dominance"?

talk

| 21:17, 24 August 2006 (UTC)

I don't remember what the technical term is either but "clear the neighborhood" is the term used in the popular press at least. If someone can locate a more technical term we should consider moving this to that and making this a redirect or making that a redirect to this with a note about what the technical term is. JoshuaZ 21:21, 24 August 2006 (UTC)

I've given a link to an excellent paper by Steven Soter on the subject, and which uses the term. I guess technically you might call it many things, for example dynamic dominance, or as Soter does, "tendency of disk evolution in a mature system to produce a small number of relatively large bodies (planets) in non-intersecting or resonant orbits, which prevent collisions between them."Derek Balsam 21:26, 24 August 2006 (UTC)

I think someone might beat us up if we move the page to that, though...

talk

| 21:27, 24 August 2006 (UTC)

tendency of disk evolution in a mature system to produce a small number of relatively large bodies (planets) in non-intersecting or resonant orbits, which prevent collisions between them Go for it! LOL Derek Balsam 21:32, 24 August 2006 (UTC)

I like Shimgray's suggestion of "

Dancter

05:39, 26 August 2006 (UTC)

It looks way better than it did...but you're right, it's still not totally accurate. It'll get there though. I'm not 100% sold on the argument regarding "clearing the neighborhood" simple because the eccentricity of its orbit takes it inside Neptune's orbit. The real question should be, given the obliquity of Pluto's orbit could it ever get close enough to Neptune to be cleared out of Neptune's orbit? Anyway, there are also problems with Pluto's gravitational pull as Charon and Pluto orbit each other with the focus of their orbits relative to each other being in the space between them. OK, I'm rambling. Sorry. •Jim62sch• 22:24, 24 August 2006 (UTC)

Hmmm. The concept of dominating an orbit is pretty solid science, and so is the answer to your question about Pluto and Neptune's orbits. Pluto and all the other plutinos are now stabilized in an orbital resonance determined by Neptune, the dominant body. So the answer to your question " given the obliquity of Pluto's orbit could it ever get close enough to Neptune to be cleared out of Neptune's orbit?" is, "not any more, because over the last few billion years the plutinos have fallen into resonance with Neptune as it came to dominate its orbital domain".Derek Balsam 01:15, 25 August 2006 (UTC)

Atually, I was being a bit of a smart-ass. Then, lo and behold, we see this: "Dr. Alan Stern, of the NASA New Horizons mission to Pluto, points out that Earth, Mars, Jupiter and Neptune have also not completely cleared their orbital neighborhoods, which would technically make them qualify as dwarf planets. Earth co-orbits with 10,000 near-Earth asteroids, and Jupiter has 100,000 Trojan asteroids in its orbital path. "If Neptune had cleared its zone, Pluto wouldn't be there," he has said." I could argue these points either way, although I tend to see flaws with the earth and asteroids bit. •Jim62sch• 00:29, 26 August 2006 (UTC)

Yup, there is some disagreement about where to draw the line. But even Dr Stern does not disagree with the concept. Derek Balsam 00:36, 26 August 2006 (UTC)

I don't either, although it's interesting to see how much debate this change in Pluto's planetary status has engendered. I think my personal preference might have been to classify Pluto and Charon as a dual-planetary system, but even that's not 100% supportable. •Jim62sch• 00:46, 26 August 2006 (UTC)

My understanding of this clearing business is this Neighbourhood of a point is a set containing the point where you can "wiggle" or "move" the point a bit without leaving the set. (from Wiki)

This neighbourhood is trem used in Topology. We can define it in simple words as

The neighbourhood of size Theta around a point P is the set of all points whose distance from P is less than Theta.This can be extended to: the neighbourhood of size Theta around a set of points S (such as an orbit) is the union of the neighbourhoods of size Theta around each point of S.

Now the problem is, we need a parameter and measurement for this neighbour hood. Then all confusion will over. In this senario we know that the parameter is km. But how much wherther it is 100 or 1000 or 10000km . The number of planets depends on the size of this neighbourhood. If the size of neighbourhood is large then almost all planets especially Jupiter, Mars and Neptune will be Dwarf Planets. So what we need now is an explanation from Astophysicts about this Neighbourhood.

The term is well defined. See reference 2 of the main article http://arxiv.org/abs/astro-ph/0608359 In that document an orbital zone is defined as follows: "Two bodies share an orbital zone if their orbits cross a common radial distance from the primary, and their non-resonant periods differ by less than an order of magnitude.", which is a pretty simply definition of neighborhood. I would add that the current neighborhood is to a first approximation the torus traced out by the orbital path of the planet's

Lagrangian points as well. But that's really saying the same thing: non-resonant, non-crossing orbits.Derek Balsam

14:40, 28 August 2006 (UTC)

The order of magnitude part doesn't affect any interesting cases (except maybe Sedna), so this is essentially equivalent to saying that two bodies share an orbital zone if their orbits cross. Which is contrived, since the definition is allegedly based on the idea that the planet has gravitationally influenced nearby objects, and gravitational influence happens when two objects are close by, regardless of whether their orbits cross. Specifying that the orbits cross seems more like an arbitrary attempt to exclude Pluto than to actually do what the definition is supposed to do. Ken Arromdee 07:53, 3 September 2006 (UTC)

None of this has any bearing on the article. If you object to the "demotion" of Pluto, I would suggest you correspond with the International Astronomical Union and explain to them why they are wrong. •Jim62sch• 13:14, 3 September 2006 (UTC)

By this definition, does it not mean that a planet cannot have any satellites? /confused. --Djedi 22:07, 24 August 2006 (UTC)

Think of it this way: it has cleared its orbit of anything that's not under its direct influence. Anything left in the orbit has either collided with it (and become part of it), been pulled into orbit around it (as a moon), or left in a synchronous orbit (like a

Kirkwood gaps (by Jupiter).Derek Balsam

22:14, 24 August 2006 (UTC)

And how does Pluto not meet this definition?--Djedi 02:46, 25 August 2006 (UTC)

Quite simple, Pluto has many other objects in its orbital domain, notably all the plutinos.Derek Balsam 02:50, 25 August 2006 (UTC)

My understanding of these things sucks, but looking at the plutino page seems to show they have different, yet similar orbits. So, I'm guessing I'm just misinterpretting, but to me for the clearing bit would that not mean you have the real potential to collide at some time in the future to be considered in the same orbit?Derekloffin 04:56, 25 August 2006 (UTC)

Remember, we're talking about objects in the *orbital domain* not necessarily the exact orbital path. Pluto is one of many very similar objects all orbiting in very similar orbits. If all of those orbits were governed by Pluto's gravity, then Pluto would be a planet. Instead, all of those orbits, including Pluto's orbit, is governed by the gravity of Neptune, so Pluto is not a planet in itself, but essentially an accessory body to Neptune...vaguely similar to the situation with Jupiter and the Trojan asteroids. --Aelffin 15:44, 25 August 2006 (UTC)

what about planetary rings, such as saturn's? if so that should be included.

Planetary rings are essentially just big smushed-up moons, they don't invalidate the concept.

talk

| 08:18, 25 August 2006 (UTC)

In fact they explicitly support the concept. They are in orbit around the planet, and being in orbit means that Saturn has cleared it's neighbourhood as "capture" is one of the three means of so doing. •Jim62sch• 12:44, 26 August 2006 (UTC)

From what I am seeing we have gone from one ambiguous term, "Clearing the neighbourhood" to another, "orbital zone". With neither being concrete defined terms. I see very little use for this article at this time. Some interesting ratios are shown but where are the corresponding list of sssb to show how the aggregate mass was determined, again ambiguous or poorly defined. Abyssoft 11:06, 31 August 2006 (UTC)

Soter's definition of the term is unambiguous; "Two bodies are defined to share an orbital zone if their orbits cross a common radial distance from the primary, and their non-resonant periods differ by less than an order of magnitude." The version used by IAU hasn't been made explicit yet but since they got results similar to Soter I expect it's something similar. Bryan 15:56, 31 August 2006 (UTC)

This term is just casual (poorly defined) working of the recent decision about Dwarf planets. Until it is better defined (it it becomes better defined), it should be left in the context of the subject it relates to. Thee is nothing here that woudl not go better in teh various articles about orbital dynamics and physics. Dalf | Talk 23:26, 24 August 2006 (UTC)

I disagree (and have reverted a merge made without any discussion). Whilst the term has suddenly come into prominence from that debate, it has a seperate meaning... In addition, why to "dwarf planet" specifically? The ruling pertains as much to planets, or to

talk

|

Oppose merge, for Shimgray's stated reasons. Clearing the neighborhood refers to planetary disk accretion and orbital dynamics in general, not just for dwarf planets. A merger to Dwarf planet would be too specific. Maybe to

Planetary orbit, though... Derek Balsam

01:10, 25 August 2006 (UTC)

Support merge, but to Definition of planet. I think that whole article probably needs to be overhauled now anyway, and it should explain each of the criteria in the new definition, including this one. This information has already been put into both Planet and Dwarf planet in summary form, but the detailed information should be in Definition of planet. I do not think there needs to be a separate article. Plus someone who is not into astronomy might look at this title and think the article is about Urban renewal. 6SJ7 01:16, 25 August 2006 (UTC)

Oppose merge too, as stated above this term is in the mouth of everyone following the recent astronomical developments. It would be nice to somehow add some astronomical reference to the title or quotes, becasue "clearing the neighbourhood" can be just a mudane expression.Dr. Guillermo A. Sanz-Berney 03:45, 25 August 2006 (UTC)

A final definition of this term will be very helpful. It should be a sub article of "Definition of Planet". For example, by some definitions Earth has done a better job clearing its orbit than Jupiter. Jupiter has

Trojan Asteroid in substantial quantities. Ergo, it could be said that it hasn't "cleared it's neighborhood" and should be downgraded with Pluto. This is an important discussion, but should be a sub article of Definition of Planet, and/or Dwarf Planet. 70.177.71.206

04:21, 25 August 2006 (UTC)

Not only that, but even the business of 10,000 near-earth asteroids (and similar) is also a red-herring, as these objects have orbital occupancy times that are O(1e7) years (I'm going off memory from Murray and McDermott Solar System Dynamics). The "clearing the neighbourhood" stuff didn't stop once the planets themselves accreted: it has been continuing ever since, and will continue as long as Mars and Jupiter keeps sending stuff down. mdf 14:36, 25 August 2006 (UTC)

I removed a comment about how the Earth, Mars, Jupiter and Neptune (and who knows what else) are now "dwarf planets". This is flat nonsense on its face, so the editor will need to come back with a seriously good, incontrovertible, reference before inclusion can be entertained. I am sorely tempted to remove the remaining paragraphs. While referenced, they are nothing more than a commentary on the recent IAU definition: we already have an article on that one, and those comments would probably be better placed there. mdf 15:52, 25 August 2006 (UTC)

It's amazing what people interpret this as meaning. I really wish they'd used a much more complex term for it, one which didn't have an "obvious" (and wrong) interpretation...

talk

| 16:02, 25 August 2006 (UTC)

I agree with the last comment and would also say that, as a non-scientist who likes to read about science, I am very surprised at the informal manner in which this was done and the informal and undefined language in which it was expressed. I have learned to expect a high degree of precision in scientific pronouncements; these resolutions are really political documents more than anything else. Rather than approve a scientific paper, they have adopted something more like what I would expect from my state legislature (and that isn't good.) As a result, the collective effort by Wikipedians to express what has happened is, predictably, chaotic and unscientific as well. 6SJ7 16:47, 25 August 2006 (UTC)

This new definition was supposed to get rid of the ambiguity that plagued the old definition, but it did just the opposite. Now, with terms like “neighbourhood” and “nearly round”, it’s more confusing than ever. Really disappointing. 206.47.141.21 17:58, 25 August 2006 (UTC)

"Nearly round" isn't the definition - it's an explanation of the definition for laymen.

talk

| 18:01, 25 August 2006 (UTC)

"an orbiting body (a planet or protoplanet) "sweeping out" its orbital region over time, by gravitationally interacting with smaller bodies nearby.": In my opinion this is not satisfactory, for instance, for Mercury. Is the orbit of Mercury clean because of the gravitational interaction of the planet, or for the much greater force derived by the proximity of Sun? If Mercury was in the Kuiper belt, would be able "sweep out" its orbital region because of its mass? Remember that it's just a bit bigger than the largest moons of Neptune... I think this definition is as arbitrary as establishing a mass and distance threshold. Maybe this article should be closed pending further clarifications of the IAU committee or the scientific community. dawide 23:08, 25 August 2006 (CET)

" Is the orbit of Mercury clean because of the gravitational interaction of the planet, or for the much greater force derived by the proximity of Sun?" um, yes, both. See

Roche sphere. It would be helpful to understand astrophysics to properly contribute to an article on that subject.Derek Balsam

22:04, 25 August 2006 (UTC)

Or maybe you can read a book on solar system dynamics? The definition as written is perfectly fine. Mercury is Mercury because of how it formed and where it is, and Pluto is Pluto for the same reason. Move Mercury out to 50AU and, la dee da, it will stop acting like a planet! The IAU definition is dynamical, and this is because dynamical processes created it, and dynamical processes maintain it. mdf 21:35, 25 August 2006 (UTC)

Despite what I've heard on other science talk pages, this seems to be yet another case of scientific consensus being determined by voting. --Uncle Ed 20:25, 25 August 2006 (UTC)

No, this is applied politics. [1] makes clear that this is a conflict between the planetary geologists on one side and the celestial mechanics on the other. Dr Zak 05:00, 26 August 2006 (UTC)

Thanks for clarifying that. I would hate go off leaping to conclusions. I always look for patterns, being a Generalist, but 'false links' are embarrassing. ;-) --Uncle Ed 13:10, 26 August 2006 (UTC)

Did Saturn "clear the neighbourhood"? After all, the planet has massive, and visible, rings. If Jupiter had done it's job, Saturn wouldn't exist, and neither would the rings. Seems to me the IAU messed it all up. 206.156.242.36 20:39, 25 August 2006 (UTC)

ok this whole debate on scientist messing up, or a conspiracy theory is just a waiste of important editing time... don't you think? before the resolution nobody argued the validity of IAU's prerogative to define planet. When the result was not what expected disenter jump yelling FOUL!! Let's just say Pluto is not a planet anymore because Rove decided it had WMD and was a terrorist cell. DrCito 21:41, 25 August 2006 (UTC)

Re Saturn, the rings prove the validity of the concept as the capture of objects is one of the three ways a planetary body clears its orbit. The comment about Jupiter simply makes no sense. •Jim62sch• 13:17, 26 August 2006 (UTC)

I agree with you re: Saturn. I do think the very statement is a value judgement and not a metric despite some miguided soul at the IAU having come up with it. Just how does one define the term "clear the neighbourhood" in any meaningful measurable way? Robovski 01:18, 27 August 2006 (UTC)

The term is subjective in that the definition of neighbourhood is somewhat arbitrary -- yes, there is a value picked to determine neighbourhood, but like it's like the measurement of a quart: yep, it's 32 ouces, or 64 tablespoons, or 4 cups, etc, but the ounce is an arbitrary measurement -- a bit bigger or smaller and the volume of a quart changes. In other words, I agree with you. •Jim62sch• 22:18, 27 August 2006 (UTC)

Personally I don't care if the spelling is US, Canadian, UK, or whatever. But

Seconded. This isn't a proper name, as far as I can tell, so shouldn't be capitalized. Bryan 03:10, 26 August 2006 (UTC)

I wrote what's below first, and had an edit conflict and had to move my comments to this page. Whoever decided to change to the British spelling without discussing it apparently doesn't know about the capitalization conventions on Wikipedia. (And should perhaps practice better the convention of discussing the issue, which I raised in my edit summary on

2006 redefinition of planet.) -DoctorW

03:18, 26 August 2006 (UTC)

I realize this is a very small issue, especially given this page's problems, but why is the word "Neighborhood" capitalized in the title of this article? Shouldn't "Clearing the Neighborhood" redirect to "Clearing the neighborhood" instead? This becomes a bit more of a problem because there is also an issue of U.S. vs. British English in the spelling. I just had to fix the same link's redirect twice. -DoctorW 03:18, 26 August 2006 (UTC)

I think the spelling should be British. Though the article cites American astronomers, the phrase is becoming famous in relation to Pluto, and the IAU statement uses the spelling "neighbourhood."(See RESOLUTION 5A) -DoctorW 03:31, 26 August 2006 (UTC)

I agree we should use Commonwealth English spelling. The "n" should be lowercase, but we need an admin to move the page.--Sonjaaa 03:35, 26 August 2006 (UTC)

Another for commonwealth english Nbound 05:30, 28 August 2006 (UTC)

Should

I think it will end up being merged with Definition of planet, which is its parent article. We just have to decide whether to keep all info about the definition of "clearing" here or there. --Uncle Ed 13:08, 26 August 2006 (UTC)

Which would be fine, but I'd rather see the issues the article has weorked out here first. •Jim62sch• 13:18, 26 August 2006 (UTC)

I think this article could be specifically reorganized around the concept of orbital mass dominance, and everything that deals more generally with "clearing the neighborhood" could be moved to the

Dancter

13:37, 26 August 2006 (UTC)

The article "Definition of planet" is already rather large, I think we should keep at least one separate article where this orbital dominance/clearing concept is described in detail. Especially considering we don't have the IAU's take on exactly what it means yet, just Soter's - they'll probably be quite similar but there could be some fiddly bits that are different. What title it'll be best put under, and whether to merge that list into it, I'm not sure. I'd prefer to let the articles evolve for a while longer before coming to an opinion. Bryan 16:35, 26 August 2006 (UTC)

I'm just concerned that we're conflating the "clearing the neighborhood" issue with Soter's concept too much. Especially with the controversies, the comments by Stern and others seem to refer specifically the phrase in the IAU resolution text, and don't seem to address the particulars of Soter's essay at all.

Dancter

22:21, 26 August 2006 (UTC)

Pretty interesting that Earth is technically no longer a planet. Preeeetty inteeerestinnng...

Such a section might very well be OR. In any case, I refer Flarn to

Near-Earth asteroid. •Jim62sch•

22:24, 27 August 2006 (UTC)

So it will be better if we rewrite the sentence as The IAU also explicitly stated that Pluto will now be considered a dwarf planet as it has not cleared the neighborhood of its orbit (vis-à-vis Kuiper Belt Objects) --Shijualex 05:13, 27 August 2006 (UTC)

OK, I'm going to throw in yet more hazily informed opinions here, but what I understand from reading this discussion page (not, you'll note, from reading the article) is that one of the means of "clearing the neighbourhood" actually involves "arranging the neighbourhood such that nothing gets in your way" (which, BTW, is a good reason to deprecate the term "clearing" ASAP).

The relationship between Neptune and Pluto is, if I've understood this point right, a useful illustration (just drafting this comment has helped me work through the logic): Neptune and Pluto, if they are in fact in the same "neighbourhood" (which, as you say, seems to be the subject of some confusion), have already "moved out of each others way". Given their relative masses, it is pretty easy to surmise that, unless it was complete coincidence, it is Neptune that has "cleared" Pluto, and not vice versa. Thus, the new definition would class Neptune as a full planet (it has cleared its neighbourhood, even of objects the size of Pluto), but Pluto as "something else".

I'm not quite sure whether the question of Pluto clearing Neptune is truly irrelevant or not, though - if, hypothetically, Neptune and Pluto were the only things left in a "neighbourhood", would the fact that Neptune had been the dominant force in the disruption be enough to define its overall dominance, and thus planethood? In practice, I guess, it makes no difference, since the important point is that Neptune is clear of Pluto and everything else, whereas Pluto is clear of Neptune, but not everything else.

Perhaps it's too easy to anthropomorphise words like "dominance" and "clearing", and understanding a more mathematical conception would render arguments of "who has cleared who" meaningless.

It's worth noting that that rewrite is factually iffy - the IAU stated Pluto was to be considered a dwarf planet, full stop. It didn't state this because A or because B; it stated it with no conditions attatched.

talk

| 10:47, 28 August 2006 (UTC)

Oh dear, I'm blathering again.

Basically, I think the different ways of "clearing", or, more elegantly, gaining "orbital dominance" should be spelled out far more prominently and clearly in the article, with clear examples of each. I'm not an expert, so I'll likely get this wrong, but even if it later has to be rewritten or supplemented based on more formal criteria, we need something like the following:

An orbiting body gains orbital dominance by, over many orbital cycles, interacting with all nearby bodies in one of three ways:

• Collision, in which the smaller body simply becomes part of the larger one - e.g. an asteroid entering a planet's atmosphere or hitting its surface ceases to exist once it has done so
• Attraction into orbit, in which the smaller body becomes trapped as a satellite of the larger, becoming a moon or part of a
  planetary ring
• Disturbance, in which the smaller body is either pushed into a completely different "neighbourhood", or is left in a stable
  trojan asteroids, or Neptune and the plutinos
  . Specifically, note that Neptune can be said to have "cleared" Pluto in this manner, but that Pluto itself has not cleared its neighbourhood.

I'm sure the wording can be much improved by using appropriate (but not obscure) technical terminology, but I think spelling it out would make fewer the cases of "yes, but what about..." on this discussion page and in readers' minds. -- IMSoP 14:56, 27 August 2006 (UTC)

I think one thing I'd like to have explained is not so much what is clearing, but rather what is not cleared. It would be nice to show the difference for Pluto and say Earth and why Pluto isn't clear while we can consider Earth to be clear. Pluto is obviously the naggy one, so using it as an example would be best.

I removed the phrase "which would technically make them qualify as dwarf planets" from the controversy secion because Dr. Stern didn't actually say that. If someone can find a cite where Stern says this, fine. Until then, let's keep this as accurate as possible and not put words in his mouth.

Correct me if I'm wrong but definition passed by IAU on August 24, 2006 doesn't actually reference Steven Soter's article. Soter's article is a separate work. In fact, the entire Details section presents details that are not in IAU's definition. Why are we giving 2/3rds coverage to ancillary information? This seems disproportionate. If we leave it in, it should be clear that Soter's article is a seperate work from IAU's definition. —The preceding

I think I prefer this approach b). What do you guys think? —The preceding

unsigned comment was added by 65.173.164.149 (talk • contribs

) 17:49, 28 August 2006 (UTC)

Methinks you have it backwards, in that the definition the IAU passed was about what defines a planet, but this article is about a dynamical process in the solar system. Why shouldn't we cite Soter or anyone else, even if "disproportionately"? I think most of the discussion about the recent IAU decision should be snipped to a single sentence, appropriately wikilinked. mdf 19:12, 28 August 2006 (UTC)

Because the official IAU definition is more important that Soter's article. Further, it's a bit unclear that Soter's definition and IAU's definition are separate works. —The preceding

unsigned comment was added by 65.173.164.149 (talk • contribs

) 19:33, 28 August 2006 (UTC)

The IAU definition already has its own article though. Do we need another one? mdf 19:40, 28 August 2006 (UTC)

Yes, but that's on the definition as a whole, not on 'clearing the neighborhood'. And on 'clearing the neighborhood', IAU's opinion is still more important that Soter's. The fact that Soter's article doesn't have it's own article shows IAU opinion's is more important.

Whether we agree with it or not, IAU will be making the official determination, not Soter. I'm not saying we should get rid of the Soter coverage, but there needs to be more balance, and it needs to be more clear that IAU's definition and Soter's article are seperate works. —The preceding

unsigned comment was added by 65.173.164.149 (talk • contribs

) 20:00, 28 August 2006 (UTC)

Actually, I'm with mdf on this one. I think you will see that when you take out the content on the broader topic of the IAU resolution, as well as the somewhat distinct Soter concept, there just isn't enough to justify a separate page on "clearing the neighborhood" apart from the section in the definition of planet article. The fact that Soter's concept doesn't have it's own article does not mean it is less important than the "clearing the neighborhood" phrase, but that noone has contributed a distinct article on it to Wikipedia. I argue that, naming aside, right now this article pretty much is an article on Soter's concept.

Soter's work does reference related work by Stern and Levison from 2002, I suspect the reason so much of the current article focuses on Soter's extensions to it is because that's the paper we happen to have an online link to use as a source for. At least, that's the reason I mainly added Soter stuff. So I suspect there's more basis for all this than a 12-day-old journal article submission.

planet formation so IMO we should leave this as a separate article for now and simply further clarify that the IAU didn't put forward a specific definition of "clearing the neighborhood" in their planet definition. Bryan

06:30, 29 August 2006 (UTC)

From the current version of Definition of planet:

It may not be entirely clear what "clearing its neighborhood" actually means. Alan Stern recently objected that “it is impossible and contrived to put a dividing line between dwarf planets and planets,” and that since neither Earth, Mars, Jupiter, nor Neptune have entirely cleared their regions of debris, none could properly be considered planets under the IAU definition. ("Pluto vote 'hijacked' in revolt".) This would appear to contradict his earlier published work: “we define an überplanet as a planetary body in orbit around a star that is dynamically important enough to have cleared its neighboring planetesimals ... And we define an unterplanet as one that has not been able to do so,” and then a few paragraphs later, “our solar system clearly contains 8 überplanets and a far larger number of unterplanets, the largest of which are Pluto and Ceres.” (“Regarding the Criteria for Planethood and Proposed Planetary Classification Schemes,”

S. Alan Stern and Harold F. Levison

, Oct.-Nov. 2000)

As you can see, Stern & Levison's paper, or some version of it, is available on the web, albeit as a postscript file. This paper may actually be the original source of the IAU paraphrase "clearing the neighborhood." If so, summarizing the debate continues to be a challenge, since Alan Stern is one of the main players on both sides. 67.168.216.176 16:56, 3 September 2006 (UTC)

Here's some of the relevant material from the paper:

The largest planetary bodies dynamically control the region surrounding them. Nearby small bodies are on unstable, transient orbits, or are locked in mean motion resonances or in satellite orbits. [Footnote: For example, the near-Earth objects are transient bodies with median lifetimes of only 10 million years, while Trojans and Plutinos are locked into mean motion resonances with Jupiter and Neptune, respectively.] We believe such a distinction is likely to be a common one in extra-solar planetary systems as well.

Our goal for a dynamical classification scheme is thus to determine whether any given body is dynamically important to the system in which it is found. Hence, we define an überplanet as a planetary body in orbit around a star that is dynamically important enough to have cleared its neighboring planetesimals in a Hubble time. And we define an unterplanet as one that has not been able to do so. It is important to note that, unlike the physical criteria for planethood, these purely dynamical criteria cannot be an intrinsic aspect of a body, but is necessarily dependent on the environment and dynamical context in which a body finds itself.

It is crucial for the reader to note that, owing to the coupled nature of N-body dynamical systems, it is not possible to write down a simple formula for whether a planetary body will clear its neighboring region. The only truly viable method for determining whether a planetary body is über or unter is to perform a series of numerical integrations.

Nevertheless, to provide a simple, heuristic feel for the nature of our proposed dynamical classification scheme, it is possible to construct a crude estimate of whether a planetary body can dynamically clear its local environment. To do so, we apply the techniques developed by Öpik (1951), which estimate the probability P per orbit that a small body with semi-major axis a will pass within distance b of a planet (assumed to be on a circular orbit) is: [sic]

Then follow several paragraphs of gnarly and difficult-to-transcribe math talk. The last relevant sentences in the section are

From a dynamical standpoint, our solar system clearly contains 8 überplanets and a far larger number of unterplanets, the largest of which are Pluto and Ceres. Interestingly, were Luna in heliocentric orbit at 1 AU, [it would be] dynamically capable of clearing its zone; as a result it would most easily be classified as an überplanet.

67.168.216.176 17:33, 3 September 2006 (UTC)

Well, I think the appropriate thing to do is to quote and cite him freely on both sides of the argument and simply make sure we point out that it's the same guy (the dates on the cites will also be of particular importance to get right). Unless he or someone else has published something since then that actually invalidates that paper, the maths still say the same thing regardless of what the guy who wrote them down now believes. I must say though, on a personal note, that although I knew this planet definition debate was bound to get silly I never expected this sort of silliness. :) Bryan 17:44, 3 September 2006 (UTC)

Dates on citations etc.

From http://adsabs.harvard.edu/abs/2002HiA....12..205S

Title:

Regarding the criteria for planethood and proposed planetary classification schemes
Authors: Stern, S. Alan; Levison, Harold F.
Publication: In: Highlights of Astronomy, Vol. 12, as presented at the XXIVth General Assembly of the IAU - 2000 [Manchester, UK, 7 - 18 August 2000]. Edited by H. Rickman. San Francisco, CA: Astronomical Society of the Pacific,

ISBN 1-58381-086-2

, 2002, p. 205 - 213
Publication Date: 00/2002
Origin: ARI
Keywords: Planets, Classification
Abstract Copyright: IAU
Comment: JD4: The transneptunian population. Eds.: A. Lemaître; H. Rickman; C. Froeschlé.
Bibliographic Code: 2002HiA....12..205S
Abstract:

We examine the question of planetary classification, making recommendations both for the criteria by which planethood should be evaluated, as well as for more detailed physical and dynamical subtype classification schemes.

And from the paper itself at http://www.boulder.swri.edu/~hal/PS/planet_def.ps:

Regarding the Criteria for Planethood And Proposed Planetary Classification Schemes

S. Alan Stern and Harold F. Levison
09 Pages, 02 Figures, 02 Tables
Submitted to the Transactions of IAU 2000: 04 October 2000
Revised: 11 November 2000
Running Title: Planet Classification: Gravity Rules
Abstract:

We examine the question of planetary classification, making recommendations both for the criteria by which planethood should be evaluated, as well as for more detailed physical and dynamical subtyle classification schemes.

The existing Wikipedia citation looks something like this:

• Stern, S. A. (2002). "Regarding the criteria for planethood and proposed planetary classification schemes". Highlights of Astronomy. 12: 205–213. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

How this document, maybe the central source material for the whole subject, should be footnoted exactly is not an area of expertise of mine. We have two different years and a number of different months to choose from, but I think these references are all to the same thing. Since it's possible to link to the actual document, probably we should. Maybe like this?

• Stern, S. Alan (2002). "Regarding the criteria for planethood and proposed planetary classification schemes" (PDF). Highlights of Astronomy. 12: 205-213 as presented at the XXIVth General Assembly of the IAU - 2000 [Manchester, UK, 7 - 18 August 2000]. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

67.168.216.176 03:19, 4 September 2006 (UTC)

shouldn't this be "orbital dominance" or something? 132.205.44.134 02:54, 4 September 2006 (UTC)

I disagree with the proposed split. The term "planetary discriminant" is used by Soter only to refer to the "μ" parameter that he calculated by dividing the mass of the object by the total mass of the other objects in its planetary zone, it doesn't refer to the "Λ" parameter proposed by the Stern-Levison paper. The section's content is currently about an even mixture of the two and I don't think there's so much of it that it warrants removing from this article. Bryan 03:31, 8 September 2006 (UTC)

Okay, so maybe it's pulled from two articles, and maybe some of this information belongs here, but It's kinda out of place to have all the math here when that's not the crux of the topic. I think it's a way good point, but the math belongs elsewhere. I think the perfect article could be written on Planetary discriminants. McKay 03:57, 8 September 2006 (UTC)

The information in that section makes up the bulk of the article removing it would make a somewhat useless article that really only goes into the controversy. I disagree with the split -- Nbound 04:06, 8 September 2006 (UTC)

There's a single equation, I don't see this as excessive. But even if it was a lot of math, why doesn't math belong here if it's math about neighbourhood-clearing? I'm afraid I still don't see the reason why this should be split out of here. Bryan 05:01, 8 September 2006 (UTC)

REally, my argument to make them seperate articles, is that they are seperate topics. Interelated sure, but seperate nontheless. McKay 13:45, 8 September 2006 (UTC)

But they're not. Stern and Levison's work was all about determining a theoretical estimate of how quickly a planet could clear its neighbourhood of other objects, Soter's work was all about determining an experimental measure of how thoroughly a planet already had cleared its neighborhood. That is exactly the topic of this article. I'm afraid I just don't understand your position. Bryan 00:00, 9 September 2006 (UTC)

Im with Bryan on this... -- Nbound 00:55, 9 September 2006 (UTC)

Let me be clear. I think the planetary discriminants should be here. The table is acceptable. But how those numbers are calculated isn't really a part of Clearing the neighborhood. It's a part of planetary discriminant. The planetary discriminants themselves are a part of the article. McKay 03:06, 9 September 2006 (UTC)

...Sorry, still completely boggled. I can't figure out what the distinction is here, or why the results of calculating planetary discriminants is okay but describing the process of how those results are achieved is not. Heck, I've even been considering merging

List of solar system objects by planetary discriminant into this article as well. I think we may have to simply agree to disagree on this matter, unless someone else can chime in and support splitting in some way I understand. Bryan

04:01, 9 September 2006 (UTC)

After reviewing the arguments, and re-reading the "clearing the neighbourhood" article, I am in favor of the split. In addition the resultant article should in truth be 3 articles, 1 for each of the 2 values ( "μ" , "Λ" ) and 1 specifically cover various planetary discriminants. Should any other values arise they to should have there own articles and be covered in the planetary discriminates article breifly. As for list of any kind, they should be separate articles both link to and from related articles. Abyssoft 14:27, 11 September 2006 (UTC)

I have no objection to articles specifically on those particular parameters existing and although I don't like the idea of separate list articles in this case it's no skin off my back if they exist too. What I don't get is why that information shouldn't be here, since they're on the topic of this article and the article is not overly large. You've stated your opinion on the matter but you haven't explained any of the reasons for it so I'm not left with any better understanding of this position. Why do you think this information should be removed from this article? Bryan 16:00, 11 September 2006 (UTC)

Rather then out right removal, I am refering to a brief synopsis of the information, with approriate links to the complete articles. This is simply a matter of proper organization. Lists while informative in terms of data tend to muddy a page and can detract from the meat of the article; hence why such lists should and are generally found on separate pages through out the wikipedia. The planetary discriminate article should be about, what is a planetary discrimate, its conception and history, and briefly touch on the various values, like ( "μ" , "Λ" ). By briefly a quick simple formula and what it represents; Leaving the background of the value to it's own article. Abyssoft 17:36, 11 September 2006 (UTC) updated for (sp) 22:17, 11 September 2006 (UTC)

I agree with Bryan. This information is being presented by non-experts based on the best sources we can find, and the presence of examples can serve to crystalize understanding where a block of awkwardly presented text may just be incomprehensible. You can look at the table and see yeah, Ceres and Pluto are different from the others, look at all the names and numbers together. Also remember this is already a "separate article," even a sub-sub-article. The main articles are probably Pluto and Planet. 67.168.216.176 02:27, 12 September 2006 (UTC)

This is Dwheeler citing himself as a source.

Not that I necessarily have a problem with that, but still ... 67.168.216.176 04:47, 8 September 2006 (UTC)

If hes not a reputable source.. then he should be removed (along with the info he presented) -- Nbound 05:37, 8 September 2006 (UTC)

it has been done (not by me) McKay 13:45, 8 September 2006 (UTC)

For Mercury to be considered a planet it clears out a ring of 2.406 AU For Pluto to be reupgraded it would have to clear out a ring of - 244.186 AU, an obviously much larger line, under the definition of Orbital Dominance. However, if we're talking about 3 Dimensional space, Pluto clears more "Neighbourhood" than Mercury by volume, correct? Hopquick 06:12, 11 September 2006 (UTC)

I dont know where you are getting your figures from... Mercury does not clear out to 2.4 AU... else it would have cleared Venus, Earth and Mars!... For pluto to be reupgraded it have to clear the Kuiper Belt and Neptune would probably have to disappear -- Nbound 06:53, 11 September 2006 (UTC)

You didn't read correctly. You're thinking Semi-major Axis. The Orbital circumference of Mercury (planet) is 2.406AU. It only had to clear out a ring around the sun 360,000,000 km in length to become a planet. The orbital circumference of Pluto is 244.186AU. Pluto has to clear 36,529,705,653km or a ring 100 times larger to be considered a planet. However, Pluto has cleared out an area on par with Mercury. It just cannot clear out the volume of its orbit because its orbit is that much larger. Put Mercury in the Kuiper belt and it would not be a planet. Compare the distance between Pluto and its Kuiper belt kin with the distance between Mercury and Venus. There is often much more space between Pluto and anything than the inner planets have with each other. Orbital dominance is an artificial determinant of planethood. Earth would not be large enough to clear out the Kuiper belt. I need to find the paper I was reading that backed this up, however I have a little one to take care of. Hopquick 19:29, 11 September 2006 (UTC)

You are right Hopquick. In millions of years Pluto would have collided with other bodies, gained mass, cleared its orbit and suitable to be classificated as a planet. But the 8 planets have already done this (Ceres has the same trouble like Pluto and its orbit is smaller than Jupiter's or Neptune's ones.). So, nowadays Pluto isn´t yet a planet.

Albireo3000 22:23, 11 September 2006 (UTC)

Actually though he's clarified what he was saying and it now makes much more sense, pluto is not a dense object (2g/cm^3), so the gravity it creates by its size is nowhere near that of Mercury (5g/cm^3), which is also much larger in diameter, and even more in volume. Its small gravity coupled with its 2:3 resonance with Neptune (along with the other Plutinos, also means that its hard for Pluto to accrete objects in its orbit as they are all travelling at roughly the same speed, Neptune is still the dominant body in that area. Ceres in a similar position, alot of the asteroids are affected by Jupiter resonance, and Ceres being small is not very massive and thus does not have much of a gravity well. The time it will take to clear out these belts is probably longer than the life of the solar system, but when they do they will be able to be termed planets. Your Earth in the Kuiper Belt comment is quite correct, as it would probably be in 2:3 resonance also, as Neptune is still by far the dominant mass. And thats the big reason why Pluto is not a planet, all the objects in its orbit are controlled by Neptunes gravity, not by its own, and this slows the accretion process incredibly. So if u want Pluto, destroy Neptune! :-) -- Nbound 23:01, 11 September 2006 (UTC)

Good notation on the problems for outer bodies like Pluto becoming planets under the new definition. Inner planets have several advantages for planetary accretion: greater differentials in orbit velocity bring co-orbiting materials into reach frequently, initial "hot" state of the system amplifiying that effect, shorter orbital periods themselves mean faster cylces in the process, probably a difference in initial system matter density. For a single star system I can see that a longer enough orbital period alone might mean that a potential planet could never catch up to enough of its co-orbit material. After all the larger the period the larger the volume/surface exposed to material wandering through from somwhere else. Sort of like shoveling a long walk during conditions of blowing snow -- at certain length of path it doesn't matter how big the person, they will never get it all clear.

But I wonder how much we are gaming the system by chosing a definition that helps prove that the planetary accretion process is unlikely at given ratio of solar mass to distance. The new planetary definition sort of sidesteps the issue of bodies having long term stability. After all if a Jupiter sized body was to pass through Earth orbit and gobble us up -- that new object would be declared a planet even if it was obviously going to spin into the sun in only a few hundred years. -CJF —Preceding unsigned comment added by 65.26.138.106 (talk • contribs)

How much "we" are gaming the system by choosing a definition? If anybody here is a professional astronomer, I'd be interested to hear about it. We could take one of the tags off. 67.168.216.176 21:25, 3 October 2006 (UTC)

I doubt that it would be, as by orbit, they would be refering to a stable orbit -- Nbound 01:00, 16 September 2006 (UTC)

• So the Earth in Pluto's orbit would be a dwarf planet by IAU's criteria? BTW plz stop adding tags to the article, the definition itself is unclear, not the article per si. Instead of an article we will end up with tags. LOL.---Pedro 21:46, 19 September 2006 (UTC)

Hard to say since the IAU criteria don't have specific numbers or equations attached to them at this point. However, the Stern-Levison Λ/Λ_E parameter for Earth under that circumstance would be 2.53×10⁻², which is comparable to Mercury's and four orders of magnitude larger than Pluto's, so I suspect by that measure it would still fall on the "planet" side of things. Assuming Earth was substituted for Pluto (ie, Pluto's not sharing its orbit too) then the Soter planetary discriminant μ would be 35.25 (assuming I'm doing the numbers right). This is two orders of magnitude larger than Ceres' μ but three orders of magnitude smaller than Neptune's μ, placing it in a much more ambiguous position. Leaving Pluto in that orbital zone as well makes things even worse. It'd come down to a question of what specific method and what numeric threshold IAU settles on. Bryan 03:40, 20 September 2006 (UTC)

Well the IAU criteria don´t have numbers nor equations to determine the hydrostatic equilibrium (nearly round) shape, as the pressure gradient is not easy to measure from Earth with observational data. An even 2 objects with the same observational (mass, density,etc... )data can have different shapes. We need models as with the clearance of the neighbourhood.Albireo3000 11:27, 20 September 2006 (UTC)

• Now I do understand why Pluto is not a planet: it is bound by an object of higher mass. It is not a moon, but a resonance object. But why Ceres and Eris are not planets? The are not bounded by any other body.--Nixer 11:44, 24 October 2006 (UTC)

Please review the rest of the talk page. Pluto is not bound by an object of higher mass, it is merely in an orbital resonance with Neptune. To understand the concept of clearing the neighborhood, it may be useful to consider what would happen if we removed the objects from the system: removing Neptune or Jupiter would drastically change the dynamics of the solar system, while removing Eris, Pluto, or Ceres, would not. Michaelbusch 16:07, 24 October 2006 (UTC)

“clear the neighborhoods around their orbits,” means that anything that is under its direct influence has either collided with it, or has been pulled into orbit around it, thats what it means right? so pluto isn't a planet because it orbit through stuff, right?

Not quite. "Clearing the neighborhood" means being the dominate mass in the vicinity of the orbit. So Jupiter outweighs the Trojan asteroids, Earth outweighs the near-Earth asteroids, but Pluto does not outweigh Neptune. Michaelbusch 22:12, 8 October 2006 (UTC)

Some one want to archive some of this? Michaelbusch 22:12, 8 October 2006 (UTC)

The talk page is less than two months old and is only 64K large so I'd suggest not archiving yet unless the size becomes truly unmanagable. Bryan 22:38, 8 October 2006 (UTC)