Talk:Clearing the neighbourhood

Programmatic Issue

I'm not sure where to report this, maybe one could guide it along the correct channels: To sort the list after values with 10x^6 and 5.6 is not only faulty and confusing but renders it as a tool useless. The Javascript sorting-code should be fixed to accept values with exponents (be it base 2, e, 10 or any other) and real-number points. —Preceding unsigned comment added by GENtLe (talk • contribs) 23:14, 29 January 2008 (UTC)

Stern's use of "clearing the neighbourhood"

Has Stern himself used this term in his papers? From everything I've read by him he supports the concept but think's the IAU definition has lousy wording. If he hasn't, this needs to be made clear in the article. The Enlightened 05:14, 13 October 2006 (UTC)

Yes, the Stern/Levison paper from 2002 used four slightly different versions of the phrase. All four were quoted in an earlier version of this article. Perhaps they should be put back in. See /Archive 1#Origin of the phrase, and what to do about Stern, above. 64.122.41.167 05:58, 17 October 2006 (UTC)

graffiti

I'm not sure where to put this, but there seems to be an extraneous bit of information on the page with the line "HE WAS BORN IN MICHIGAN IN 1946" near the top of the page.

24.159.236.28 06:57, 25 October 2006 (UTC) Mentor397

What are the cleanup tags actually asking for?

This article is accumilating various pastel-shaded boxes at the top that request work be done, but I can't easily tell exactly what it is that's wrong with the article. Why does this article need the attention of an expert? What sort of information on this subject would be "more general"? Which bits of the article are confusing to some readers? Bryan Derksen 17:56, 11 April 2007 (UTC)

From the edit history:

• {generalize} added 11th April by User:Wassermann "Please generalize for lay readers"
• {confusing} Added Sept 2006 by User:JianLi, no reason given.
• {expert-portal|Astronomy} Has been there from day 1, seems abundantly satisfied by now. PaddyLeahy 14:11, 26 April 2007 (UTC)

I'm taking out the confusing and expert tags, in that case. As for generalizing, I'm still not sure what can be done about that. The subject isn't a general one. Bryan Derksen 17:40, 28 April 2007 (UTC)

Probably not clear from the first few sentences of the intro what it was about; I have rewritten. I hope you also don't mind that I've renamed this to cleared the neighbourhood - this is the far more common term, it's what the definition refers to; the process of "clearing the neighbourhood" is not really given much discussion in the article anyway. —The preceding unsigned comment was added by Abu-Fool Danyal ibn Amir al-Makhiri (talk • contribs) 16:44, 16 May 2007 (UTC).

Use of Λ_E

As written, the article notes that bodies with a Stern-Levinson parameter Λ > 1 have "cleared a substantial fraction of small bodies out of [their] orbital neighborhood[s]", and implicitly those bodies with Λ < 1 have not "cleared the neighbourhood." Yet the table lists values of Λ normalized to the value for Earth, although the cited Soter article lists the actual (approximate) values for Λ in Table 1. To me, this seems like a disconnect between the text of the article and the table, and confusing for the lay reader. I would rather just be able to see at a glance whether the Stern-Levinson parameter for a body is less than or greater than 1, which is the important distinction, rather than the value of the parameter relative to Earth's value. This is why I added a note giving the value of Λ_E and the values of Λ for the other 10 bodies relative to 1. Can someone explain why the table in this article (and associated tables in related articles) uses Λ/Λ_E, rather than simply Λ? Spiderboy12 14:15, 19 September 2007 (UTC)

Perhaps this is in order to make the article more clear for the casual reader? Even if they are unfamiliar with this concept and just want to do some light reading, Λ/Λ_E gives a frame of reference for this value, as opposed to some arbitrary number that they know little about. 204.85.24.5 (talk) 18:42, 15 February 2008 (UTC)

But the only point of the parameter Λ for the casual reader (who only knows about Λ from this article) is the Λ > 1 vs. Λ < 1 distinction - the frame of reference is "cleared the orbit or not". Unless I'm mistaken, that's the whole point of the Λ parameter. This is an arbitrary parameter created for that purpose, and isn't something like mass or orbital period where the reader has at least a vague sense of Earth's value. If someone really wants to know what the values are compared to Earth, we'll still have the Earth value in the table. -- 76.204.102.226 (talk) 15:23, 24 August 2008 (UTC)

I agree, so I added in a column for Λ. I also added a column for where Λ=1 for that body, saying how far out it could be to be a planet, since some have claimed that Mercury wouldn't be a planet if it was in Pluto's orbit. I used k=0.0043, with units in Yg and AU. Tbayboy (talk) 17:07, 21 February 2009 (UTC)

What values are you using for the materials within the orbits? Jupiter would not dominate its orbit if it was surrounded by Jupiter-sized objects. Serendi^podous 19:53, 21 February 2009 (UTC)

Λ doesn't depend on the co-orbital materials, only the semi-major axis (or the period), the mass, and the approximately constant K (taken from the paper). One of Stern-Levison's goals with Λ was that it could be used outside the solar system, without needing to know unknowable (for the foreseeable future) data, i.e., small bodies. Soter's planetary discriminant is the one that needs the material estimate. Λ is a theoretical value indicating whether a body will clear it's orbit of small bodies, and μ is an observational value of how much a body has already cleared its orbit. Λ=1 is just kinda cool since it shows that Mercury would eventually clear out the Kuiper belt (if it was in, say, Quaoar's orbit), and that Pluto wouldn't clear out the main asteroid belt (if it was in Ceres' orbit). It's all just plugging the numbers into the equation shown on the page. Tbayboy (talk) 23:58, 21 February 2009 (UTC)

A related request, not strictly applicable to this page. Please could somebody with appropriate expertise, so not me, write an article defining and explaining the Stern–Levison parameter. It seems to be really good discriminant between planets and smaller things, but what is it? JDAWiseman (talk) 11:57, 1 October 2013 (UTC)

Further to previous request, the Stern–Levison paper is at boulder.swri.edu/~hal/PDF/planet_def.pdf and was quite helpful (though the explanation of the equations assumed more expertise than should Wikipedia). JDAWiseman (talk) 15:56, 9 February 2014 (UTC)

There's not much more to it than what is stated in this article, other than a bunch of math. They wrote an equation to figure out the probability of clearing a particular small body of given orbital parameters, then applied it to the numbers they had for the main belt objects to get the K. Is that value applicable to the trans-Neptunian domain? For Wiki purposes, have you seen many other papers refer to and use this parameter? Tbayboy (talk) 04:03, 2 October 2013 (UTC)

Well, there is an article on Mass–energy_equivalence, so one equation can have an article. What are the parameters, conceptually how do they lead to the probability, and so forth? For me, the ‘conceptually’ is the most important. I’m imagining a ten-minute lecture to keen undergraduates. JDAWiseman (talk) 17:27, 23 November 2013 (UTC) (And sorry about the slow response.)

Request added to Requested_articles/Natural_sciences#Astronomy JDAWiseman (talk) 14:08, 26 November 2013 (UTC)

Naming

This name is a bit cnfusing if you don't know what it should be about. A correct name should have "". Nergaal (talk) 03:59, 28 January 2008 (UTC)

Well, now when you pinpoint it: true. Who (or what) clears which neighborhood? It's not possible to guess from the title what topic is treated. Maybe "Clearing the neighbourhood (planet dynamics)"? ... said: Rursus (bork²) 09:53, 12 March 2009 (UTC)

I agree that the current title of this article ("Clearing the neighbourhood") is awkward. A decent encyclopedia deserves more fitting titles for its articles. In the article I added the definition that "clearing the neigbourhood" is a "criterion" (adopted by IAU). An article named The criterion of "clearing the neigborhood"' may be too long, or is it OK? Any better suggestions? Or how about moving it as a section of IAU definition of planet? --HYC (talk) 22:13, 23 October 2009 (UTC)

That article is quite long already. It's a phrase, and the most common one at that (or perhaps "cleared the neighbourhood", since we aren't really talking about the process but the fact of having done so). It's not obvious from the title who feeds what multitude either, but specifiers are for when there are other notable uses of the phrase. --99.245.206.188 (talk) 23:22, 20 February 2010 (UTC)

K?

Okay, this article has now been around a while. Re this part:

where k is approximately constant

...will someone please take the time to define k? Or has IAU become a secret society and this is a secret that we're not allowed to know? —Preceding unsigned comment added by 204.4.13.72 (talk) 22:27, 11 February 2008 (UTC)

Don't expect the IAU to be self consistent. It's constantly contradicting itself. Every time they gather to meet, Zombie Feynman heads the other way in search of brains. 24.254.163.150 (talk) 17:40, 14 June 2008 (UTC)

Oh, also, the reasoni t's "approximately constant" without an actual definition is so that they can adjust the value if need be to keep Pluto on the non-planet side of the line. Really, none of this had any kind of scientific motivation behind it, just arbitrary prejudice. I ridicule them for being rediculous. Did you know that their definition passed resolution with a 4% vote? That's not 4% more, that's 4% of the society voted to pass the resolution. The rest went home in disgust before the vote happened. 24.254.163.150 (talk) 17:58, 14 June 2008 (UTC)

ROTFL! Shouldn't we consider deleting this Hype-advertizing article? It's probably just designed to inflate the egos of the planetary dynamicists - kind of blatant self-advertizing, maybe? Said: Rursus ☻ 20:28, 28 July 2008 (UTC)

Well, since Alan Stern is one of those being "hyped", I can't say that only the dynamicists egos are being massaged here. Serendi^podous 13:19, 12 March 2009 (UTC)

Suggest adding information in table for Makemake (dwarf planet)

I recommend adding information about Makemake (dwarf planet) to the data table in the article showing planets and dwarf planets. (I'd have done it myself except I don't have the corresponding numbers.) 63.111.163.13 (talk) 21:37, 16 July 2008 (UTC)

What is k?

If "k" is "approximately constant", then what is its value? It could change the outcome of the equation radically if it is greater than or less than 1. Serendi^podous 07:47, 8 August 2008 (UTC)

The precise value of k does not matter, because only the ratio $\Lambda /\Lambda _{E}$ is important. The k is cancelled out. Ruslik (talk) 10:43, 8 August 2008 (UTC)

So is it possible to calculate Makemake's $\Lambda /\Lambda _{E}$? Serendi^podous 13:11, 10 August 2008 (UTC)

Yes, it is possible. Ruslik (talk) 13:54, 10 August 2008 (UTC)

Can we do it? Serendi^podous 08:37, 11 August 2008 (UTC)

---

The statement that, "the precise value of k does not matter..," does not seem correct. As stated everywhere, k is not a constant (even if it is close to a constant). The formulas for $\Lambda _{P}$ and $\Lambda _{E}$ would therefore be better presented as:

$\Lambda _{P}={\frac {k_{P}M^{2}}{P}}$

$\Lambda _{E}={\frac {k_{E}M^{2}}{E}}$

Since $k_{P}$ and $k_{E}$ cannot be assumed to be the same value, they cannot be mathematically cancelled in the consolidated equation. (Merely another issue with the IAU definition.) CoyneT ^talk 19:03, 23 September 2008 (UTC)

Are you claiming that k varies by a factor of a million from object to object? Unless you are, then I don't see what issue this creates. The entire point of that formula is a quick and easy way to determine what is likely to be a planet and what isn't from very easy to determine parameters, and the resulting values split the two groups by over a million times, so as long as the k value is even vaguely similar then the formula serves the purpose it was designed for. Also it is not part of the IAU definition, which doesn't need to be more than vague about the difference at this point for the same reason. --86.161.73.15 (talk) 17:35, 16 December 2010 (UTC)

Note that the above comments (by Ruslik) about k are wrong. $\Lambda$ is the predictive measure of the scattering ability of the object, scaled so that 1 is the uberplanet threshold for clearing the orbit versus not clearing (in a Hubble time, roughly 14 billion years). If you drop k, then you have to replace the threshold 1 with $1/k$, which gains you nothing. $\Lambda /\Lambda _{E}$ simply states it as a fraction of Earth's scattering power, which is not very meaningful, since then you would need yet another constant to be the uberplanet threshold (instead of 1).
k itself is a function (an integration) based on the orbits of the small bodies being scattered, their inclinations and eccentricities, which relates to their relative velocities (to the scattering body). k doesn't change much within the solar system's disc, since the bodies are mostly all going the same way. IIRC, Stern-Levison used a k derived from observations of the main asteroid belt. It would be very different out in the Oort cloud (anywhere beyond the original protoplanetary disc), and it might get significantly different as you get very close to the sun. So CoyneT is technically correct, but the difference in ks is too small to be significant over the domain we're concerned with here. Tbayboy (talk) 16:38, 17 December 2010 (UTC)

Need to add Haumea

Haumea_(dwarf_planet) needs to be added to the "In the Solar System" table, since it's now been officially declared a "dwarf planet". Dave (talk) 18:24, 23 September 2008 (UTC)

Wow. Thanks. Missed that one. Serendi^podous 18:38, 23 September 2008 (UTC)

Either Eris or Pluto is wrong in the table

According to the table, Lambda_Eris < Lambda_Pluto, but Lambda_Eris/Lambda_E > Lambda_Pluto/Lambda_E

It looks like the Eris/Earth ratio here is wrong. According to Soter's paper (the reference for that column), it should be 1.33e-8 (.002 / 1.5e5, versus the 1.41e-8 you would get from using the numbers in the lambda column, since Soter probably used slightly different Eris mass/AU numbers as his paper was published in 2006). Note that Soter didn't publish the ratio, so it looks like whoever calculated it here twitched a finger. Either sets of numbers (lambda columns or Soter's with lambda_Pluto = .003) will give reasonably similar results with the Pluto ratio being greater than the Eris ratio. Tbayboy (talk) 23:28, 8 June 2009 (UTC)

Since whoever made the Lambda/Lambda_Earth column hasn't appeared, I fixed the entry using Soter's numbers. Tbayboy (talk) 21:09, 21 June 2009 (UTC)

Definition official yet?

Did the IAU ever get around to defining the term, "clearing the neighborhood", say at their 2009 meeting? As I recall, that was left undefined in 2006. -- KarlHallowell (talk) 20:48, 8 December 2009 (UTC)

Especially interesting since even Jupiter has not "cleared its neighborhood" of Trojans, and can't... 2.31.162.113 (talk) 03:50, 7 March 2015 (UTC)

"Clearing the neighborhood" does not mean that there can be no other objects in similar orbits, but that the object controls its orbital zone: Jupiter has its trojans locked in trojan orbits, a specific form of 1:1 resonance. Those trojan are completely dominated by Jupiter. Those that are not in a very specific orbital configuration with Jupiter are quickly scattered away. That is what it means to be able to clear one's orbit. --JorisvS (talk) 08:38, 7 March 2015 (UTC)

The question that I have is, did Mercury clear it's neighbourhood, or did the Sun help??? Poor old Pluto has a 200+ year orbit, meaning a HUGE amount of very 'busy' space, and is supposed to clear the neighbourhood all on it's own before it gets to be a planet, while Mercury has a relatively tiny amount of neighbourhood to clear and has a very, VERY big 'helper' to do all the work for it. Seems a bit unfair. And given that we now know that Pluto doesn't have any craters, doesn't that mean that it HAS cleared it's neighbourhood, given that it obviously hasn't hit anything lately? How big is the 'neighbourhood' and when and how, exactly, is it determined that it is cleared? FillsHerTease (talk) 00:15, 15 November 2015 (UTC)

The sun does not help Mercury clear anything away, and Pluto does have craters. Tbayboy (talk) 16:06, 15 November 2015 (UTC)

Clearly the Sun most certainly did help Mercury clear it's neighbourhood - that's obvious and goes without saying - but you're right, it turns out that they have discovered craters on Pluto. They are old craters though and as such they are not relevant to this debate. The questions are:

1. Why is Mercury considered to be a planet when it didn't clear it's own neighbourhood itself?

2. How big is the neighbourhood around Pluto?

3. When is the neighbourhood around Pluto considered to be clear? This needs to be properly defined.

4. As there are no new craters on Pluto, it could be argued that it's neighbourhood is already clear. Obviously there can be no argument though - either way - until Pluto's neighbourhood is defined.

5. How is it determined that Mercury's neighbourhood - or the neighbourhood of ANY planet for that matter - is completely clear? At any stage a body like Senda - one with an enormous orbit which passes through the neighbourhood of one or more planets - could be discovered. What would happen then?

The problem with the definition is that it is too rough and could lead to one or more planets having to be demoted, or the definition being updated, at some future stage. It's bad science... FillsHerTease (talk) 04:49, 28 December 2015 (UTC)

No, the Sun did not help Mercury clear its neighborhood any more than it helped other bodies clear their neighborhood. With respect to the other questions, the IAU has not defined what "clearing the neighborhood" means in a quantitative manner (there was no resolution proposed on this topic at the General Assemblies in 2009, 2012, 2015). It is possible to write down a criterion for what it takes to clear an orbital zone of a specific extent in a specific time interval (e.g., "A Quantitative Criterion for Defining Planets"). JeanLucMargot (talk) 06:08, 28 December 2015 (UTC)

Food for thought

Consider the Saturnian moons Tethys, Telesto and Calypso. These moons share an orbit, where Telesto and Calypso lie in the 4th and 5th Lagrange points of Tethys. Now imagine we find a group of extrasolar planets of Earthlike (or even larger) size that orbit their star in a similar way, which we will almost certainly observe someday. Then doesn't this "clearing the neighborhood" business become a bunch of BS? ChessA4 (talk) 03:12, 24 April 2010 (UTC)

By the current definition they wouldn't be planets at all, as they don't orbit our sun. 24.18.124.254 (talk) 08:35, 31 July 2011 (UTC)

The current definition doesn't apply outside of the solar system, so it doesn't say that they're not planets. As an analogy: Belgium has a bunch of laws and regulations saying who is a police officer. But they only apply to Belgium. That doesn't mean that there aren't cops in Japan. Here, a separate committee of the IAU is responsible for defining extrasolar "planets", and they haven't finalised a definition yet. See Extrasolar planet. Tbayboy (talk) 15:38, 31 July 2011 (UTC)

Note that Telesto and Calypso are way smaller than the dominant Tethys. Dione has a similar configuration with two much less massive moons (Helene and Polydeuces). The orbit of the protoplanet Theia in a Lagrangian point of Earth apparently became unstable when its mass exceeded ~10% (about the mass of Mars) of the mass of Earth, ultimately having led to a collision with Earth. So it seems that such a configuration requires one heavy, dominant object and one or more smaller objects in orbit around an even far heavier central object. So maybe it's more appropriate to think of such a configuration of multiple round objects as one planet with one or more dwarf planets in Lagrangian points?

And then there could also be similar-mass (non-Lagrangian) co-orbital objects with a relationship like the one Epimetheus and Janus have (and which Earth and tiny 3753 Cruithne also have). I'd say that if, say, Venus and Earth were to share their orbits in that way, both could still be considered planets. They would both gravitationally govern each other's orbit, but not disturb it (as such a configuration is stable), so that the other's mass is excluded from determining one object's planetary discriminant, as explained in the article. This then contrasts with non-planets such as trojan objects, the asteroids, or TNOs, which either have little influence on the orbit of a dominant object (planet) in their orbital zone and have their orbits governed by it (if present), or chaotically disturb other non-planets nearby (but to an insufficient degree to remove them from their orbital zone). --JorisvS (talk) 22:43, 7 August 2011 (UTC)

Speaking of food

What does "cheese" mean in the table? At first glance, this appears to be vandalism, as it's not explained elsewhere in the article, but it's been in the article now for a couple of years. - BilCat (talk) 00:15, 12 May 2011 (UTC)

Where do you see the word "cheese"? --Ckatz^chat_spy 04:52, 12 May 2011 (UTC)

The problem was vandalism to Template:Esp, per this diff, but it's been fixed now. I should have thought to check the templates! - BilCat (talk) 09:00, 12 May 2011 (UTC)

Ceres planetary discriminant

The planetary discriminant for Ceres is given as 0.33. Is this really the correct number? Ceres has about one third of the mass of the asteroid belt, but the definition of "planetary discriminant" has mu= mass(Ceres) / mass(Ceres-crossers). Which means if mu = 0.33, then the mass of Ceres-crossers would be 3 times that of Ceres, and not all of the asteroids in the belt cross Ceres either. So, was the discriminant actually computed (meaning there are many Ceres-crossers outside the belt), or just copied in? Ambi Valent (talk) 09:53, 7 October 2012 (UTC)

Not just the mass of the crossers (and grazers), but all objects sharing its orbital zone. --JorisvS (talk) 14:02, 8 October 2012 (UTC)

Orbital zone IS the crossers (as explained in the article). The 0.33 is taken from the paper, so we can't do anything about it here. I think Ambi Valent's concern is valid in principle, but doesn't really have any practical effect: Vesta, Pallas, and Ceres all mutually cross, and each alone is enough to disqualify any other (the threshold is 100). Similarly, in the trans-Neptunian belt, Eris and Pluto range far enough to disqualify each other and everything else short of Neptune. The true value of any particular discriminant won't be exactly Soter's values, but, since they all fall short by orders of magnitude, a ballpark estimate is good enough. Tbayboy (talk) 17:24, 8 October 2012 (UTC)

Not exactly, think of just-not-grazing minor planets. Planets would clear those too. In fact, crossing per se does not do it. Consider, for example, two Jupiter-mass exoplanets in exchange orbits or in moderately eccentric crossing orbits stabilized by a 2:1 resonance. Logically, this would then also apply to Neptune and Pluto (this still means Pluto is a dwarf planet, but for a somewhat different reason: the Kuiper belt). --JorisvS (talk) 17:56, 8 October 2012 (UTC)

Just to be clear, the paper defines the orbital zone as if they share a common radial distance at some point in their orbits. I.e., the perihelion of the outer object is within the aphelion of the inner. Soter also excludes resonant objects and "comets". (I was interpretting Ambi Valent's "cross" to mean that, but I think you're interpretting it to mean one object crossing another's semi-major axis, and "grazing" as overlapping but not crossing the semi-major axis. I like your definition better.) Tbayboy (talk) 19:37, 8 October 2012 (UTC)

I had meant "Ceres-crossers" as objects with a perihel distance smaller than Ceres' aphel distance and an aphel distance greater than Ceres' perihel distance. Anyway, I prefer the Stern-Levison parameter Λ when it comes to determine which object is a full planet and which isn't.Ambi Valent (talk) 21:47, 10 October 2012 (UTC)

The real objection to the new planet definition is that it takes into account not only the mass or physical size of the planetary body...but its location (i.e. orbit). This doesn't matter (too much) for very massive bodies, but for objects at the very boundary of the definition it matters a lot. Look at the table in the article -- if Pluto is moved from the Kuiper Belt to the orbit of Venus (0.8 AU or less), its "clearing the orbit" ratio becomes greater than 1.00 and it qualifies as a planet. For Eris, the qualifying orbit is roughly 1 AU (Earth's orbit). Many astronomers are uneasy with a definition that depends on *where* the object is in the Solar System...because that makes the definition look like it was finessed to include just the eight most massive bodies (and to exclude the next 10 or so qualifying bodies). It has the appearance of being scientific...without being so at all. Imagine if a college had a qualifying formula that took into account your GPA *and* how many miles away you were from the university (i.e. a particular score would get you in *if* you were 300 miles away, but not if you were 1,500 miles away, etc.). It would be clear that the formula discriminates against those with borderline GPA scores. The union could have achieved its goal with a simple definition that said "are you rounded by gravity? are you in orbit around the sun -- and only the sun? are you 1,000 miles in diameter (or more)? If yes-yes-yes you are a planet. That would put Pluto and Eris in the group (and probably 10 more Kuiper Belt objects) and keep all the lesser stuff out. But they didn't want to do that. Thus, a Mars-sized body at 150 AU is not a planet...but at 90 AU it is a planet...which is nonsensical. The article needs more content on the opposition to the formula 66.19.84.4 (talk) 00:50, 24 August 2013 (UTC)chesspride

That's a real concern. I remember some comments around the time of the definition debate, which said that there are two main bodies of opinion - that of people such as plantary geologists, who consider the body in isolation, and are therefore interested in whether it is in hydrostatic equalibrium etc; and that of people who are interested in solar system dynamics, and are therefore interested in interaction between different bodies. In my view, the IAU was quite wise in realising that the planet/not-planet boundaries are significantly different, depending on the type of science under consideration, and that we therefore need a 3-way classification. Planetary scientists would therefore be interested in the boundary between (planet + dwarf planet) and (other objects), while solar-system scientists would be interested in the boundary between (planet) and (dwarf planet + other objects). Bluap (talk) 02:25, 24 August 2013 (UTC)

It's not really a concern. There was (and is) little call (although non-zero) for making Mimas and Ganymede planets. If Earth was where Ganymede is, it wouldn't be a planet. Location matters. As Mike Brown pointed out, cleave nature at the joints. There's no joint between round and non-round, but there's a huge one in orbital dominance. Tbayboy (talk) 04:57, 24 August 2013 (UTC)

Yes, satellites, even those that are the size of (small) planets, are seldom considered "planets". This means that location clearly does matter! --JorisvS (talk) 14:34, 1 September 2013 (UTC)

Where have you seen opposition to the formula? Or even mention of it? There is some opposition to the concept of using clearing as the discriminant, but I haven't heard of any complaints of either of these specific formulae. Tbayboy (talk) 05:04, 24 August 2013 (UTC)

I agree with editor "chesspride" on the Mars-sized body aspect of this. The obvious flaw in the new planetary definition from the start has been that we can't be certain how objects got to be where they are. (Did they form as planets within the solar system...or as something else or somewhere else?) Essentially the current "clearing" definition serves as a mass cut-off for non-satellites. As Stern has noted, this was done in reverse order to obtain a given a lower object count. This contrived cut-off works at the moment because of the ~20 fold difference in mass between the largest known dwarf planets and the smallest inner planets. However, who is to say that a relatively large (e.g. half the mass of Mercury or greater) but distant object won't be discovered? The object will easily fail this "clearing" criteria. For this and other reasons, the definition doesn't seem scientific...particularly when it states that "dwarf planets are not planets." That's like saying short humans are not humans. (The IAU shouldn't have called them "dwarf planets" if they weren't planets at all...something about subsets that I learned way back in early elementary school.) Good luck with rationalizing the IAU's present definition, it falls short--yes, pun intended. Red Harvest (talk) 07:25, 4 April 2014 (UTC)

It is a common fallacy to require a mass or size criterion for planethood. Clearing the neighborhood is about dominance, not about size. Dwarf planets are usually smaller than planets, but need not be. It is quite scientific; in fact, a criterion based on size or mass will need an arbitrary (i.e. non-scientific) cutoff to lead to 8 (or 10) (known) planets. You could call dwarf planets 'planets', but that makes no difference: the major real-world difference between the dominant 8 and the other round bodies remains. --JorisvS (talk) 11:42, 4 April 2014 (UTC)

That is a strawman argument as I didn't set the criteria, I'm observing it's effect. It is largely about size, because the combination of mass and location is what sets "dominance." But if you put any of the inner planets far enough out they are also no longer planets. Furthermore, the current 3rd criteria was attained in a non-scientific manner: to specifically exclude bodies, while at the same time still calling them planets with only a qualifier in front. Creating a rigged test to get a specific result doesn't exactly inspire trust or confidence in the methodology. I don't have a problem with the dwarf planet nomenclature for Pluto, Ceres, Eris, etc., but I do have a problem with the IAU claiming something they've named a planet is not a type of planet. That's such obviously twisted logic that even elementary school kids start guffawing about it. And why is that the IAU decided to create such a hilarious contradiction? It appears that they were unwilling to take the next logical step at the obvious break point between the giant outer planets and the much less massive inner planets and create more defined subsets of planets. (For illustration compare the mass ratio of Neptune and Earth: 17:1 with that of Mercury and Pluto: 25:1 or Mercury and Eris: 20:1.) Stern does a very good job of breaking all of this down in the following article: http://www.space.com/9594-fighting-pluto-planet-title-planetary-scientist-alan-stern.html Dwarf planets are still merely a subset of planets, just as dwarf stars are still a subset of stars whether or not said stars have "dominance." Red Harvest (talk) 08:37, 5 April 2014 (UTC)

It is quite common for an X Y not to be Y (i.e. a dwarf planet is not a kind of planet, nor is a minor planet; a sea lion is not a lion). --JorisvS (talk) 18:21, 5 April 2014 (UTC)

Orbital dominance was already something Alan Stern himself noted. He only gave different terms to the same categories as those formalized in the IAU definition; the awkward semi-German "überplanet" and "unterplanet" for the IAU's "planet" and "dwarf planet"; the only upside was that in his terminology there is a term for planet+dwarf planet ("planet"). In spite of different terminologies, the concepts are identical. --JorisvS (talk) 18:27, 5 April 2014 (UTC)

Where did Stern say that dominance was used to achieve the pre-determined number? I find that hard to believe, since it was Stern himself who made the division (uber/unterplanet) well before the IAU addressed the issue (and even then, the IAU started with roundness, not dominance!). The dominance gap is not just an idiosyncracy of our system but a consequence of the physics. As for "dwarf planet", there were few complaints about "minor planet" for well over a century. Similarly, for roundness, there were no petitions to reinstate Ceres to planethood. The previous silence on these issues shows that these objections to the IAU definition aren't about science, but the emotion of Pluto. Tbayboy (talk) 13:34, 4 April 2014 (UTC)

I'll add that it is, of course, no coincidence that the planets are all much bigger than the known dwarf planets. The more massive an object, the more easily it can scattered other objects or sweep them up, and the more easily it clears its orbit. Stern talks about "dynamically important" objects or objects that "dynamically control" their surroundings.[1] I'd say that's clearly the same thing as 'dominance'. --JorisvS (talk) 15:15, 4 April 2014 (UTC)

überplanet

Can someone get rid of the garbage about überplanet and unterplanet? — Preceding unsigned comment added by 112.118.143.28 (talk) 08:19, 15 December 2013 (UTC)

It's not garbage: it shows the development of the concepts leading to "dwarf planet". Tbayboy (talk) 17:58, 15 December 2013 (UTC)

Planetary scientist's understanding.

The article said Most planetary scientists understand "clearing the neighborhood" to refer to an object being the dominant mass in its vicinity, for instance Earth being many times more massive than all of the NEAs combined, and Neptune "dwarfing" Pluto and the rest of the KBOs.

Neptune has not cleared its neighborhood because it dwarfs Pluto and the KBOs. Pluto is disregarded because its orbit prevents it from colliding with Neptune, and Neptune is not a KBO in any case. Saros136 (talk) 15:12, 5 October 2014 (UTC)

True, the relative masses do not matter. It has cleared Pluto from its orbit. Specifically, it has put Pluto into a resonant orbit so that Pluto never comes close to it. That Neptune does this shows it gravitationally dominates its orbit. As for Earth, though, NEAs are continually cleared and replenished; that the dominant body is Earth can be seen from the relative masses, but this is not the reason for the dominance. --JorisvS (talk) 15:24, 5 October 2014 (UTC)

Problem

How do you define orbital period if say the Sun is moving around the Galaxy, the Galaxy it self is moving and even where the Earth moves away from the Sun is completely different during each "orbital period."

You would say dominate body in its orbit, but is it? The dominate thing in any planet's orbit is not the planet, but the dark energy and dark matter in its orbit.

And wouldn't it make more sense to have true definition rather than arbitrary ones for the convenience of the market place, rather than actual science? Hmm?

Think about this? Is the sun, the center of our universe? It is not, then we do we morph our understanding of space to fit the criteria as though it is for an untrue view of our cosmos as a simple means to satisfy our market? Science and the market should be two separate things. We shouldn't be morphing our understanding of reality just to make a quick buck. — Preceding unsigned comment added by 70.160.104.223 (talk) 17:47, 7 November 2014 (UTC)

Simple: As seen from a co-moving reference frame. And dark matter and dark energy do not have a measurable effect within the Solar System. --JorisvS (talk) 19:02, 7 November 2014 (UTC)

Trojans / L4, L5.

Stupid laypersons question. As I understand it, Trojans (masses at Lagrange points 4 & 5) share the same orbit with the body under consideration for planethood, yet are stable so would not be cleared. So clearing the neighborhood, as I understand the definition, would mean Jupiter was a dwarf planet as it has a shared orbit (co-orbital configuration). Could the article be made clearer so I can see where my thinking is going wrong, please? — Preceding unsigned comment added by 31.50.82.206 (talk) 12:53, 15 July 2015 (UTC)

Actually, resonant orbits, such as that of the trojans (1:1) with mostly Jupiter or Neptune, are a special case of clearing the orbit. They have been put in a very specific configuration that is only possible with a dominant object, i.e. a planet. Similarly, Neptune has the plutinos, with Pluto the most prominent example, in resonant (2:3) configuration, which can cross Neptune's orbit. Again, this is a special case of clearing the neighborhood. And even if it weren't, like in the case of the near-Earth objects, for example, the combined mass of the objects is so small that nearly all of the mass is still in the planet whose orbit they cross (see the μ in the table). --JorisvS (talk) 15:41, 15 July 2015 (UTC)

Dimensions (i.e. physical units)

$\Lambda ={\frac {M^{2}}{a^{\frac {3}{2}}}}\,k$

Would someone be able to add the physical units to this equation, so that the result becomes dimensionless, as seen in the remainder of the article. Alternatively, what is the approximate value (including dimensions) of k. Tomeasy _{T C} 05:50, 16 September 2015 (UTC)

In reference #3, apparently, the formula they use is

$\Lambda ={\frac {M^{2}}{P}}\,k$ .

With

$P=2\pi {\sqrt {\frac {a^{3}}{GM_{Sun}}}}$ ,

these are essentially equivalent, though with different ks:

$k_{WP}={\frac {\sqrt {GM_{Sun}}}{2\pi }}k$

Within the Solar System the relationship between k_WP and k₃ is simply a constant. In reference #2, the mass they use in (4) is apparently μ = M/M_☉, basically a body's mass in solar masses, but with the thing dimensionless. Thus, the whole thing between the square brackets almost corresponds to k_WP, but not quite.

Anyway, because Λ is a dimensionless number, the dimensions of k necessarily have to cancel out those of the variables. k_WP = [kg² AU^−3/2] (if a in AU, which is often most convenient). For the one in reference #3, it's k₃ = [kg² yr⁻¹] (again most conveniently with P in [yr]).

As for the value of k, it varies somewhat with the orbital parameters of the small body. Reference #2 does give an estimate, saying "the average value of the term between the square brackets is 1.7×10¹⁶ years", but that would not make Λ dimensionless, which is a mistake on their part. All elements of the term between the square brackets except τ, G, and M_☉ are dimensionless. G is 6.674×10⁻¹¹ m³/(kg⋅s²), with τ in [s] and M in [kg], the term between the square brackets has dimensions [kg² m^−3/2] (which is the same as [kg² AU^−3/2], just with a conversion factor). That would be good if they used M as here on Wikipedia, not μ, because in their case it does not make Λ dimensionless. Just plugging in the number they give (disregarding the given dimension) with the mass of Pluto and its semi-major axis in [AU] does give a value close to the one they state (0.003 vs. 0.004), and for Ceres gives their stated value. --JorisvS (talk) 10:41, 16 September 2015 (UTC)

Thanks for the detailed analysis. I can only add that Figure 2 in this reference (which I was hoping would shed some light because it defines for which ratio mu/a^(2/3) lambda takes the value 1) is equally bogus. The y-axis coordinates of the points shown should be obtained easily: mu and the orbital period are easy to find for all planets. However, mu is dimensionless and the orbital period is time, so taking the logarithm does not make much sense unless you make some implicit assumption on time specified in years and the unit being dropped (or better formal division by the constant c=1 yr). But even if you ignore this (and try out years, day, hours, seconds) you do not end up with numbers so small as the y-coordinates would suggest not even without taking the logarithm. If I take the logarithm of the ratio, as the axis title suggests, I get rather negative numbers than small positive numbers - but again, one may assume this was not the intention of the authors.

Unfortunately, I do not have anything positive to offer. I am just very sceptical about reference 2 and basing our article on it. I still have to read reference 3. Maybe, this makes more sense. In the end, using lambda = k * M^2/P could be an appropriate alternative. Tomeasy _{T C} 16:54, 16 September 2015 (UTC)

Figure 2 plots μ²/T with orbital period T in years. It also says so in the caption, but the axis header is just crap. --JorisvS (talk) 18:47, 16 September 2015 (UTC)

I tried years, but it does not work at all: Uranus_mu = 14.536 and Uranus_T = 84 years, so the fraction becomes 2.515. You may want to try the log of this, which gives 0.4. Both values, however, have absolutely nothing to do with Uranus' y-coordinate, which is 1e-11. Tomeasy _{T C} 19:03, 16 September 2015 (UTC)

For example. Jupiter has a mass of 1047.56⁻¹ solar masses. Square this and divide by its orbital period (11.8618 yr), which gives 7.7×10⁻⁸, which is what is plotted in figure 2. Same applies to the other objects, though some may be plotted a bit crudely. --JorisvS (talk) 19:11, 16 September 2015 (UTC)

Right. I confused mu to be a normalization by Earth's mass, whereas it is the Sun's. 21:41, 16 September 2015 (UTC)

The expression for Λ given in Stern is the same as in Soter, just substitute Kepler's third law connecting M, a, and P (of course, k is then different). The units in Stern's eq.4 all cancel out, but I think their comment about the the bracket units is wrong, it's distance with exponent 1.5 (matching that of the semi-major axis outside the brackets). Tbayboy (talk) 23:15, 16 September 2015 (UTC)

Apparently, I wasn't quite awake when I wrote my above. The units are k_WP = [AU^3/2 kg⁻²], k₃ = [yr kg⁻²], and the term between the square brackets in #2 [m^−3/2], so that does make Λ dimensionless. --JorisvS (talk) 10:33, 17 September 2015 (UTC)

In case of the Earth, the article's list states lambda = 1.53e5. With the units you suggest (ie. AU, kg), this would give k = 4.29e-45 AU^3/2 kg⁻² for the formula that is given in the text. Correct?

If we agree on the above, why then not think in terms of SI units (ie. m, kg). This would give a somewhat larger (still extremely small) value for k = 2.47e-28 m^3/2 kg⁻². As I understand it, the choice of units is free and only the numerical value of k will change accordingly, while k's dimension is tight to the formula we choose to present for lambda (ie. function of distance or function of period).

In order to get "reasonable" k-values, we could also use this M_+ symbol, representing the mass of Earth. In this case, we could write that for the Earth, k = 1.53e5 AU^3/2 M_+⁻², which obviously equals the numerical value of lambda. Didactically, this may be the best option ...

Another topic. The lambda values shown in the list, where do they come from? I find very similar ones in Ref 3, however, at a lower digit precision. Any idea why this is? Tomeasy _{T C} 20:11, 17 September 2015 (UTC)

Stern-Levison give the value of k (1.7e16, I forget the units but they're easy enough to determine by working backwards from their results). I did that some years ago to get the k=0.0043 for units of Yg and AU, and moving the solar mass into k (as you did): the results then closely matched Soter. With those units and k, calculations are easy even on limited calculators. The numbers in the table here are from the table in Dwarf planet (see the formula there), using that k and the then-best mass for Ceres, and adding Haumea (a bit off now) and Makemake (the mass on it's page at the time, since removed). The precision here is unwarranted, and unnecessary since order-of-magnitude is enough.

What bothers me most about Λ is the "approximately constant" k, which they derive by averaging a bunch of main-belt asteroids. Would k differ significantly if they used a bunch of TNOs? I find it hard to believe that Jupiter would clear an orbit at near 100 light years (from the Λ=1 calc). Tbayboy (talk) 23:27, 17 September 2015 (UTC)

Jupiter doesn't (I find it hard to believe, too), but the time scale used is 12 Gyr and at Λ = 1 the scattering power is very limited. Λ is really 'the likelihood that a small body will suffer an encounter that leads to a deflection of magnitude Γ'. But there are many minor bodies; are all supposed to find themselves near this Jupiter-at-100-ly at some point? Also, as you say, their method of estimating that term is by looking at Ceres and taking the orbits of belt asteroids, which may not be the best way. Why not just evaluate its dependency on eccentricity, inclination, and semi-major axis numerically? This suggests to me that Λ = 1 may well not the best choice of cut-off? Anyway, they do note that the only viable method is really just numerical integrations, which seems prudent especially in such extreme cases. --JorisvS (talk) 09:28, 18 September 2015 (UTC)

k is a function of the orbit and shows small variance for different orbits considered. So, we will not be able to state one k value and claim it is valid for all. But if we specify it for a specific orbit, the reader may understand the order of magnitude being handled by it, and I think the order of magnitude is the same withín the solar system.

To me it appears most obvious to select Earth's orbit for this purpose. Tbayboy, note that I was using Earth's mass as a unit in one of the examples - not the Sun's. With this choice, and choosing AU as a unit for the semi-major axis, the formula given for lambda in the article collapses straightforwardly to lambda = k * 1 AU^-3/2 M_+², or equivalently, k = 1.53e5 AU^3/2 M_+⁻². I think this conclusion is simple enough not to be labeled as original research. Moreover, the formula for lambda as well as the lambda value for Earth are well sourced.

I propose to add this. Tomeasy _{T C} 07:41, 19 September 2015 (UTC)

The only k we have is for the asteroid belt. Deriving it from Earth's lamba is incorrect, since that lambda was calculated from original belt k and not a k from derived from small bodies in the Earth's orbital zone. All you're really doing with your Earth-k is changing the units of measurement to Earth masses, not deriving a new k for that zone. That then means that to calculate a lambda you first have to convert the body's mass from kg to Earth mass. It's more convenient to keep it in kg. Yg is also a conversion, but it's just sliding the decimal. It also happens to be very near Ceres mass. The k we really want is one derived from the trans-Neptunian belt, since that's where all the DPs are. Tbayboy (talk) 14:38, 19 September 2015 (UTC)

Maybe I do not understand this completely, but when the article states that lambda = 1.53e5 for the Earth, has the source used the wrong k-value for this? Has it used another formula than the one we show? Tomeasy _{T C} 18:08, 20 September 2015 (UTC)

There is only one k value used (modulo unit conversions, pulling in the solar mass, and any period-to-a conversion) in all the calculations, by the sources and on the wiki-pages, which was derived from main-belt asteroids. You seem to be trying to derive a new k from Earth's lambda, but that doesn't make sense since lambda is not measured, but something that is derived from k. In this case, Earth's lambda was derived from the asteroidal k, so your rearranging of the equation doesn't do anything other than re-state the asteroidal k using a different unit of mass, Earth masses. k might depend on the orbital zone, but the source indicates that it doesn't vary much ("approximately constant"). Tbayboy (talk) 22:09, 20 September 2015 (UTC)

What about making a plot as a function of i, V_∞, and V_p for Γ=1/2 and seeing what that gives us? --JorisvS (talk) 14:04, 21 September 2015 (UTC)

Indeed Tbayboy, I was just rearranging and using convenient units. The aim of this is to state in the article what value of k underlies the lambda values shown in the list. Maybe, you are right and the scientist have used "the wrong" k value for this, but even that could be mentioned somehow: Eg. "The lambda values presented in the list have been calculated with a k value of ..., which is based on the main-belt asteroids orbital properties." In doing so, at least the reader would be given an order of magnitude feeling about this constant and be able to estimate lambda values for arbitrary objects with mass M and distance a. I tried it out for some of the planets mentioned in the list, and it works pretty well. So, at least my initial question is answered. I think it worthwhile to put this information in the article. Tomeasy _{T C} 20:24, 21 September 2015 (UTC)

Ah! I misunderstood what you were asking for. For the first equation in this section (the one expressed with "a"), k is 1.7e16 from the article, where you enter the body's mass in solar masses, but I forget what unit "a" is in, probably km. It converts to 0.0043 if you want to use Yg for the body's mass and AU for the semi-major. Just slide the decimal if you want to use kg instead of Yg (4.3e-45). Tbayboy (talk) 22:38, 21 September 2015 (UTC)

Indeed. With k = 1.53e5 AU^3/2 M_+⁻², AU = 149,598,000 km, M_+ = 5.97e24 kg = 5.97e3 Yg, we can express k in many other units. Eg.: k = 1.53e5 AU^3/2 M_+⁻² = 7.85e-33 km^3/2 kg⁻² = 7.85e9 km^3/2 Yg⁻² = 4.29e-45 AU^3/2 kg⁻² = 4.29e-3 AU^3/2 Yg⁻². The last two are the ones you mentioned.

What I want to propose is that we should use AU and M_+ to state the value of k in the article. Most importantly because this is the best choice from a didactic perspective. Our target is to explain the subject in a way that allows the reader to understand it as easily and as deep as possible. With AU and M_+, the reader will quickly be able to identify the same numerical value in list, ie. the lambda value of the Earth. Understanding the relationships in the formula and its magnitude will be supported like this.

Moreover, Earth's mass, M_+, is commonly used as a unit in Wikipedia articles of planets, dwarf planets, and trabants. At the same time, AU is a common unit to measure the semi-major axis of these objects. Certainly, on a solar system scale, M_+ and AU are much more palpable than km and Yg.

I would add this information as a footnote to the column heading for lambda in the list. Here, we know for sure that this is the lambda value that was used, independent of the question whether it is the appropriate value. Tomeasy _{T C} 20:29, 22 September 2015 (UTC)

k includes U = V_∞/V_p, where V_∞ is the velocity of the small body relative to the planet and V_p the velocity of the planet, and its radial component U_x. These are not obviously constant throughout the Solar System, V_∞ and V_p certainly aren't, though it's not clear to me whether this would cancel out in U. --JorisvS (talk) 15:38, 19 September 2015 (UTC)

Add Jean-Luc Margot's planet discriminant?

Astronomer Margot proposed a planet discriminant Π which is proportional to M/(a^(9/8)), which means it falls steeper towards 1 with growing distance than Stern-Levison's scattering parameter. Margot discussed a looser variant (planets needs to clear just its feeding area) and a stricter variant (stability criteria, observed spacing of exoplanets). For Mercury, these would mean it could only successfully clear an orbit up to 29 AU from the Sun (loose) or 18 AU (strict); for Mars, the values would be 53 AU (loose) and 32 AU (strict). Should Margot's discriminant be added to the article and the table? Ambi Valent (talk) 04:13, 1 December 2015 (UTC)

I have been considering it, too, but I'm a bit fuzzy on how he calculates the scattering. I was hoping to find some of his sources for that, but I haven't had time recently. Π seems cleaner than Λ, since it seems based on the physics of the situation rather than the statistics of a particular set of bodies (Λ's "approximately constant" k). His acknowledgements section mentions conversations with Levison, Soter, Lineweaver, and others, so it seems a good candidate for "best to date" characterisation of clearing. As you allude, it's not a fixed formula, but a template formula that can be parameterised by the size of the orbital zone to clear and the speed of clearance. Tbayboy (talk) 05:09, 1 December 2015 (UTC)

In the paper he was using a template formula with different parameters, but in the proposal he published in the Astronomical Journal, he used the values that return the loosest requirement and rounded the result. See here: http://mel.epss.ucla.edu/jlm/ Ambi Valent (talk) 00:21, 2 December 2015 (UTC)

Need to add Planet Nine.

I think Planet Nine should be added.

In case it's helpful, I uploaded a figure showing that Planet Nine would clear its orbit https://commons.wikimedia.org/wiki/File:Margot2015OrbitClearingCriterionWithPlanetNine.png JeanLucMargot (talk) 22:01, 23 January 2016 (UTC)

Not here, until it's actually discovered. Should be okay in the Planet Nine page. The expected eccentricity is a problem here, too. Maybe P9 will spur work on that front (nudge nudge wink wink). Tbayboy (talk) 06:23, 24 January 2016 (UTC)

Unbalanced tag on Disagreement section

I have placed an unbalanced tag on the Disagreement section of the article as it is plainly written from the point of view of someone opposed to the IAU definition; it gives no arguments in favour of that definition and gives little weight to the views of its proponents.

I question whether this section should be in the article at all. It has no bearing on the meaning of 'clearing the neighbourhood' but instead is concerned with whether or not 'clearing the neighbourhood' should be a criteria in the definition of a planet. This should really be covered in articles relating to such a definition. All that is needed here is a paragraph noting the dispute and linking to the relevant pages. Cuddlyopedia (talk) 02:53, 27 January 2016 (UTC)

Thank you. I agree with your assessment. The recent rewrite of that section is neither neutral nor factually correct. JeanLucMargot (talk) 04:54, 27 January 2016 (UTC)

I reverted it. Aside from being unbalanced, it also overwhelms the article, and makes a minor issue seem like a major issue. There have been several IAU meetings since, and there hasn't been enough opposition to re-open the issue. If it belongs anywhere, it's in a dedicated article on the whole DP controversy. Tbayboy (talk) 05:03, 27 January 2016 (UTC)

Hello everybody,

I see your point that it overwhelmed the article, but I spent a whole day researching it and I tried to write it from a neutral perspective, so it was not a "rant". I gave arguments for the other side, though apparently not with balance so I will try to improve that. I also agree it probably should be a separate article.

However, the current section is itself not neutral and needs improvement. The main problem is that it mischaracterizes the disagreement and I was trying to fix that. The article brings up Stern's disagreement with declassifying Pluto, so it already puts the disagreement into the context of the planet definition. I didn't add that, I only tried to balance it. A more substantial part of the disagreement focuses on how "clearing the neighborhood" is an extrinsic property whereas some people say we should use only intrinsic properties for classification. That disagreement is completely relevant to an article about clearing neighborhoods, especially one that has a "disagreement" section, doubly so when that section puts it into the context of planet definitions. Per the neutral POV policy on balancing aspects: "An article should not give undue weight to any aspects of the subject but should strive to treat each aspect with a weight appropriate to the weight of that aspect in the body of reliable sources on the subject." I provided many references from reliable sources to show that this other issue is part of the disagreement on "clearing neighborhoods". The article should at least name all of the disagreements (or else it should name none of them) and then it should provide a link to an article that deals with all of them in full.

Also, since this section cites only Stern, it communicates the unbalanced idea that only one significant person is disagreeing, which undermines that perspective (in reality 400 planetary scientists signed a petition in 2006 to protest it, and the leadership of the AAS Division of Planetary Sciences criticized it, as did other significant scientists). And BTW, the reason it hasn't been brought up in later IAU meetings is only because planetary scientists know it would fail in another vote because the non-geoscience astronomers favor the present definition, in part out of a desire to move on. The fact that it hasn't been raised in another IAU meeting isn't relevant to this discussion. I gave references for all these people disagreeing with various aspects of clearing the neighborhood.

The article also violates neutral perspective in the way Stern's statements are uncharitably characterized. When Stern said that not even Earth has cleared its orbit and therefore fails the IAU definition, that isn't a "shift" from his 2001 paper in the least, since the whole point of that paper was to propose a specific metric that the Earth does not fail. By interpreting Stern in this uncharitable way, making it sound as though he shifted his arguments after Pluto was declassified (which suggests to the average reader that Stern's arguments derive from bias rather than from reasoning), the article is taking sides.

I agree in retrospect that some of the other disagreements I had included are better in an article on the overall planet/DP controversy since they are not specifically about the efficacy of clearing orbits or the valid application of clearing orbits.

If my edit failed to achieve balance then then it should have been corrected (and made smaller), not removed. Reverting it violates the intent of this policy:

As a general rule, do not remove sourced information from the encyclopedia solely on the grounds that it seems biased. Instead, try to rewrite the passage or section to achieve a more neutral tone.

I provided sources for everything that I wrote and the text will give readers a much better understanding of the nature of the disagreements. Calling what I wrote a "rant" to justify deleting it wholesale violates the Wikipedia policy to assume good faith. Furthermore, I feel it violates the intent of the "do not bite the newcomers" guideline. Although I'm not a newbie to Wikipedia, I am a newbie in editing this article. Wholesale deletion of an entire day of research made to improve the article isn't very welcoming.

I request JeanLucMargot to let me know what he sees as factually incorrect. Everything I wrote was reporting what other scientists have said as part of their disagreement, and they were all sourced, so unless I misquoted them then it couldn't have been factually incorrect, by definition. Their opinions are what they are. If there is something I am missing here please let me know what it is so when I work on the sub-article (trying to achieve more balance) and on this article (keeping what you said above in mind) then I can avoid any factual errors. Sanddune777 (talk) 01:46, 28 January 2016 (UTC)

Here is one example (among many) of misinformation. The statement that "400 planetary scientists signed a petition in 2006" is patently false. First, 305 people signed the petition. Second, people of all stripes, not just professional planetary scientists, signed the petition: electrical engineering, meteorology, countless students, etc. Among the signatories is someone who believes that the influenza virus emanates from Venus and is blown to Earth by the solar wind. Even though the organizers of the online petition had access to over 9,000 IAU members, less than 1% of IAU members signed it. The facts of "Clearing the neighborhood" are well explained in the article. The fact that a few people happen to have a preference for an alternate planet definition may deserve a brief mention, as in the current version. JeanLucMargot (talk) 02:45, 28 January 2016 (UTC)

Sorry about the "rant", it was a reaction to the size rather than the content, to making a mountain of a molehill. I think the content is better placed as a sub-article off of IAU definition of planet. However, it will always suffer from one-sidedness because those who agree with the IAU definition have little motivatation to produce defending press reports. Tbayboy (talk) 04:45, 28 January 2016 (UTC)

Sanddune777: I'm sorry that a day's research got deleted; but the results of the research are simply in the wrong place. Hopefully, you can utilise the research somewhere more appropriate. What's needed here is a relatively short note that the controversy over 'clearing the neighbourhood' is not so much over the concept itself but the use of the concept in the definition of a planet and to the imprecision of the concept in the IAU definition. However, I do agree that the current section is itself somewhat not neutral and could be improved. If no-one objects, I'll give it a go in the next day or so. Cuddlyopedia (talk) 07:42, 28 January 2016 (UTC)

OK, make it within a week. Sorry, life interruptus! :) Cuddlyopedia (talk) 13:33, 31 January 2016 (UTC)

To hurry things along I took a stab at it. 132.170.212.41 (talk) 15:42, 8 March 2016 (UTC)

Apologies -- I wasn't signed in. This was me. Sanddune777 (talk) 15:48, 8 March 2016 (UTC)

Now it is synth-y with "has shown that the vagueness is correctable". Has he ever claimed that the vagueness is correctable? Or that the definition would be acceptable with such a fix? If he has, he is contradicting his comment quoted in the previous sentence ("if Neptune has cleared it zone..."), as well as his statement in the source "it is impossible and contrived to put a dividing line between dwarf planets and planets", which is exactly what he did with uber/unter-planet. I don't think Stern's self-contradictions belong in the article (as previously), but neither should we put words in Stern's mouth. The vagueness complaint is echoed by Brown and others, but Stern is not just arguing against vagueness of the wording, but against the whole relevance of the concept being used in the definition. Tbayboy (talk) 20:13, 17 March 2016 (UTC)

I changed the wording to avoid being synthy. It wasn't intended that way, but I agree it could be read that way. Please see if this fixes it. Stern's statement that you cited here, "...it is impossible and contrived to put a dividing line between dwarf planets and planets," is taken out of context. Here's the full quote:

It's an awful definition; it's sloppy science and it would never pass peer review - for two reasons. Firstly, it is impossible and contrived to put a dividing line between dwarf planets and planets. It's as if we declared people not people for some arbitrary reason, like 'they tend to live in groups'. Secondly, the actual definition is even worse, because it's inconsistent.

The reporter then summarizes Stern's second argument where he says that major planets also fail to absolutely clear their zones, and it ends with another quote from Stern, "If Neptune had cleared its zone, Pluto wouldn't be there." It is this second argument (not the first one) that deals with the incompleteness of clearing zones, and Stern only says "the actual definition" (its wording) is "inconsistent" (not impossible). It is his first argument that contains the word "impossible", but there he is discussing the meaningfulness of intrinsic definitions, not the absoluteness of clearing zones. His illustration of separating classes of people makes this point. He isn't saying it is impossible to create sorting criteria that put people into groups; he is saying that people are intrinsically people despite how we group them, and it is impossible to make it otherwise with a definition. This is the thrust of the word "impossible" in context. Also, please looking at Stern's quote more carefully, because he didn't say it is impossible to put a dividing line between dwarf planets and major planets (unter- versus uber-). Rather, he said it is impossible to put a dividing line between dwarf planets and planets. He believes dwarf planets are still intrinsically planets, a subcategory of planets. He is saying it is impossible to make dwarf planets not be a subcategory of planets because they are still intrinsically the same types of objects. So here again there is no self-contradiction. I searched the web some months ago and found only one obscure bulletin board where somebody made a similar claim that Stern has contradicted himself. Today, I was unable to find anything making this claim. It certainly isn't in the news anywhere, and so it shouldn't be made into an issue here. We can report controversies but we can't create them where they don't exist, and Stern supposedly contradicting himself is not a notable controversy outside of this discussion. One way to change this article is to take the focus off Stern and instead quote several people saying the IAU's current definition is vague and should be changed or should not be changed based upon how we apply it in light of these discriminants. I think that would be a more meaningful summary of the public discussion related to this concept of "Clearing the Neighbourhood".Sanddune777 (talk) 19:20, 20 March 2016 (UTC)

I don't buy that argument (it's circular), but I think we agree that the whole issue doesn't belong here (nor anywhere else that doesn't serve beer). Under the worst reading, he's guilty of changing his mind, which is certainly not a fault for a scientist.

Your change fixed the synth issue I had, but now it's back towards the original problem, where, at least by juxtaposition, it's underscoring the (let's call it) irony of his previous work being used against his position. Is there any need for the second paragraph in this section? It's already mentioned in the Criteria section. If a counter-argument is needed, we only need refer back to the Criteria section to show that there are ways to meaningfully interpret the criterium as written. See also Brown's analogy of having a clean room. Tbayboy (talk) 18:32, 24 March 2016 (UTC)

I wouldn't make a circular argument and I didn't. Here is the main thing about this: it's not realistic to believe a scientist as accomplished as Alan would publish a paper defining a concept then go around saying that exact concept is impossible to define---unless he had subsequently written another paper disproving his earlier one for some particular reason. Saying Alan is doing this is an extraordinary claim, and "extraordinary claims require extraordinary evidence." I've looked at each of Alan's quotes and not only are they not extraordinarily clear in contradicting himself but in fact can be better understood without supposing he is contradicting himself. I speak with Alan frequently (I'm on a committee with him right now) and I have also heard him speak about Pluto many times during the past year. In many of these contexts he demonstrates that he still believes we can distinguish dwarf planets from major planets as different dynamical categories. (It sounds crazy to me to even have to say this, since it is so obvious.) For example, notice how he affirms this in this 2011 interview:

Suppose that in your mind, you created a solar system exactly like ours, except at each of the orbits of the nine classical planets, you put an Earth. As you go further outward in the solar system, you cross a boundary where Earth is no longer able to clear its zone, because the zone is too big. It turns out that happens around the orbit of Neptune, maybe Uranus. So you would have nine identical objects, six of which you would call a planet and three of which you would not. They're identical in every respect except where they are.(http://www.space.com/12710-pluto-defender-alan-stern-dwarf-planet-interview.html)

Notice that he directly acknowledges that orbit clearing is accomplished for six of these bodies but not for the other three, and that we can tell which bodies fall into each of the two categories, that we can even predict it ahead of time, and that we could form a classification system based on it (although he argues it would be an unhelpful classification system for people who study the bodies themselves). If Alan had indeed switched his views since his 2000 paper then he could not have given this recent quote. On the other hand, when he says at other times that not even Earth has "cleared its orbit", he isn't contradicting what he said in the above, recent quote; he is just lampooning the IAU's vague wording because taken literally it implies an absoluteness that no planet ever accomplishes. (By the way, Mike Brown has also used lampooning to make an argument opposing Alan.)

So what really are the disagreements? I know of two that could possibly be discussed: (1) the question whether the IAU's inclusion of "clearing the neighbourhood" was sufficiently precise as-worded, and (2) the question whether this concept should ever be part of the definition of a planet. As far as I can see (as a planetary scientist faculty member) everybody agrees that the IAU definition is vague as presently worded, and I don't know anybody (including Alan) who believes it is impossible to define orbit clearing criteria precisely enough to form a dynamical classification system. (And if anybody really wants, I can ask Alan to clarify what he means and whether he has contradicted himself. We will have an in-person committee meeting in a couple weeks and I will have opportunity to discuss it with him.) As far as I can tell there is no disagreement on the first of these two possible issues and there never has been. So that leaves only the second possible issue.

One option is to take out the disagreement section altogether. Another option is to state that the IAU's definition has been criticized for being vague, but the section title should be changed because it isn't a disagreement (everybody agrees that it is vague) and it is not a criticism of the orbit clearing concept (just a criticism of the wording of the IAU's definition, which is the subject of a different article). I think including it this way would be fine, but I think it would be better to state (simply) that there is disagreement on whether the orbit clearing concept should be part of the definition of a planet because it is an extrinsic rather than intrinsic property of planetary bodies, and then give a link to the main article on that topic.Sanddune777 (talk) 05:08, 3 April 2016 (UTC)

The argument made by Stern is incorrect. The Earth clears its orbit at 1 au, and it clears its orbit at 40 au, and it clears its orbit at 400 au. Stern's imaginary solar system would not have planets and non-planets under the IAU definition. It would have only planets. Stern and Levison computed what it would take to evacuate small bodies to infinity, which is not what the IAU definition requires. Perhaps this section should state that Stern misunderstands or misrepresents what clearing an orbit means. JeanLucMargot (talk) 18:26, 3 April 2016 (UTC)

A few problems with that. First, it would be synthesis to put that in Wikipedia. There aren't any sources outside Wikipedia making the explicit claim that Alan is making this kind of mistake or unethical behavior. (And are you seriously saying Alan is unethical??? I know him to be a very ethical person.) Second, it is arguably not true and needs to be settled in peer reviewed journals. If you run a simulation of that hypothetical solar system you will probably see that although the bodies at 20 or 30 AU are indeed able to clear their Hill radii, the huge population of small bodies will stay sufficiently nearby that perturbations return them into orbit-crossing trajectories too frequently to say the orbits are really cleared. The bodies can keep on clearing their Hill radii over the duration of the solar system but there has to be an element of staying clear to be clear, or at least this is an arguable position someone can take. Has anybody run a simulation to see if the small bodies will (in large part) diffuse beyond 40 AU in a relevant timescale for this kind of solar system or else form into well-behave belts between the planets? If it takes the age of the sun for 9 Earth-sized bodies to move most of that mass beyond 40 AU or into well-behaved belts then clearing the 9 individual Hill radii won't let them enjoy a relative absence of orbit-crossers over a relevant timescale. I suspect nobody has done this simulation and until it's been done and passed peer review then Wikipedia shouldn't accuse Alan of misunderstanding or misrepresenting the nature of orbit-clearing. It needs to take place in a peer reviewed environment. And third, your counter-argument brings up another aspect of Alan's argument (he was saying orbit-clearing is not an intrinsic characteristic of the bodies). If the overall dynamics of the N-body system does diffuse the small bodies outward on a fast timescale in some cases but not in others, or that the small bodies form well-behaved belts between all of the Earth-sized planets in some cases but not others, then it is definitely not an intrinsic feature of the individual bodies (it is a system-wide phenomena) and so Alan's reason for giving the illustration is still valid. Until it's been shown in simulations that the solar system--as a system-- clears the orbits, then the counter argument is question begging. In any case, it can't go in Wikipedia without sources.Sanddune777 (talk) 20:12, 3 April 2016 (UTC)

The description of orbit-clearing as an impeccable state ("absence of orbit-crossers") is not what the IAU intended. This is obvious from the IAU resolution (a reliable source), which describes orbit-clearing and provides a list of 8 solar system bodies that can clear their orbits. JeanLucMargot (talk) 21:28, 3 April 2016 (UTC)

I see your point that the resolution's footnote implies clearing isn't absolute and therefore Alan's lampooning (where he criticizes the lack of a specific metric by saying its absence implies absolute clearing) can be criticized for that reason. But putting this in Wikipedia would still be synthesis because there are no sources that go through that argument as you have done here. I don't see any sources saying, "The IAU's definition as-worded is adequate because the footnote clears up the vagueness." If there were, then that could be placed against Alan's argument as a disagreement. The IAU resolution is a citeable source about itself, but it is not a source for the derivative arguments. Presently I see several people (including yourself JeanLucMargot) saying to the press that the definition as-worded is not adequate, but I don't see anybody saying to the press or in published papers that Alan's particular way of criticizing its inadequacy is wrong.

Note that Mike Brown has also used lampooning when he criticized an alternative proposal, the one supported by the AAU's DPS. Mike says it would have included more than 53 bodies as planets, and thus it would have been a "no ice ball left behind" policy. This is not technically correct and could have been criticized since the geophysical definition of a planet leaves the vast majority of ice balls behind, those that aren't in hydrostatic equilibrium. The point of lampooning is not to be technically perfect, but to bring some inadequacy into sharp focus so people can grasp it, perhaps using hyperbole as Mike did. Attacking Mike Brown's "no ice ball left behind" statement on grounds that it technically misrepresented the DPS proposal would miss the point. Similarly, attacking this one of Alan's arguments that it isn't technically correct or complete for whatever reason is missing the point. The point is that the IAU definition fails to provide a measurable criterion, something everybody agrees with. Sanddune777 (talk) 15:42, 4 April 2016 (UTC)

I asked Alan to respond to the criticism that he contradicted himself and I just got his response. Here is my question to him.

When you point out that not even Earth or Neptune have cleared their orbits, does that mean you no longer believe it’s possible to define orbit clearing in a precise way as you did in 2001? Or are you simply pointing out that the IAU definition failed to be specific?

Here is his response:

Fair question. About the point below, I am saying as I have long said, that the IAU’s statement on orbit clearing was sloppy. It speaks to cleared zones, not the ability to clear zones, and as we know, no planet’s orbit in this solar system is cleared (else there would be no NEAs, no trojans of Mars or the giant planets, no Plutinos in MMRs that cross Neptune’s orbit, etc.), this is in part because there are stable niches (1:1 librators as one example) and because there are always new sources of objects injected once a zone clears. The point of this particular criticism is to highlight the rushed and sloppy nature of the IAU definition, adopted in violation of its own rules, in the rush to get out of Prague. Science should not be sloppy, and scientists should not respect definitions with such clearly sloppy, flawed language.

This does not contradict his 2001 paper, and it does not imply that orbit clearing must be impeccable to be part of a dynamical definition. He is just criticizing the sloppy language that resulted from a rushed and flawed process. Obviously he knows we can define dwarf planets.Sanddune777 (talk) 18:27, 4 April 2016 (UTC)

(Not sure where the indent goes here...) Re "circular": while trying to decide to what group the label "planet" is applied, the argument pre-supposes that his preferred group is the correct one, and then calls the alternate labelling illogical because it isn't his labelling. (I don't want to dissect Stern's arguments further here, since this is not a forum and it's not relevant to this page, but if you want to go to user talk...)

Re the section itself: The second paragraph ("However, Stern himself...") should be removed, since it's about Stern himself and not the issue, and since it's substance is already in the article twice before. If Stern's comment is intended as a lampoon, then it shouldn't be quoted here either. I agree with either of your suggestions: 1) "...better to state (simply) that there is disagreement ... and then give a link to the main article on that topic"; or A) just remove the section since it really applies to the definition of planet, and not what is intended by the phrase "clearing the neighbourhood", which is what this article is about, and which by itself doesn't have any disagreement. Tbayboy (talk) 01:26, 6 April 2016 (UTC)

Error in value for k in Margot's Π section?

In the Margot's Π section it is stated: "Using Solar masses for the unit of mass for the star, Earth masses for the unit of mass for the planet-candidate, and AU for the unit of distance for the semi-major axis, k = 833." For Earth, these are all 1, so the formula for Π given reduces to Π=k and therefore Π should be 833 for Earth. However, in the table, taken from Margot's paper, the value for Earth is given as 810. Thus suggests the figure for k given in the article is incorrect. Comments? Cuddlyopedia (talk) 08:04, 30 January 2016 (UTC)

Great observation! The paper shows a number of 1.9e-4 in the equation (which is what I used), but that has been rounded to two digits from the nominal value of 1.91e-4 (nominal because it's based on the duration of the Sun on the main sequence, so it's a fuzzy number to begin with, and there's another number that looks rounded figuring into it, too). Using 1.9e-4 gives k=816, which was the number I used to calculate Π for Haumea and Makemake, and all the Π=1 values. I don't see 833 anywhere in my notes, so thats just an entry error. Using 1.91e-4 gives k=812 (so the 810 is rounded from there). The difference doesn't actually change any of the table values, since they're rounded. I'll fix the k. Tbayboy (talk) 15:41, 30 January 2016 (UTC)

Glad I wasn't seeing things! Great work on the table by the way. :) Whilst writing: In the table, I notice that for all the planets Λ>Π whereas for all the dwarf planets Λ<Π. Does this always hold, or at least when either/both value is not close to 1? If so, might be worth noting that unless the object is near the boundary it's only necessary to work out one of these, as the other follows. Cuddlyopedia (talk) 13:41, 31 January 2016 (UTC)

I don't know if it always holds, but it looks that way. The two equations are similar (after removing the star portion): a power of mass over a power of the semi-major axis (or, equivalently, the period), with a constant to scale it to a threshold of 1. Also look at where they equal 1. It would be interesting to plot a graph of that, to see how they compare. Also interesting the the 1 value for Jupiter: Π has it clearing out to a light year, Λ has it out to 100 ly. I find Π more believable.

Is it worth changing the M in the Stern-Lev equation into a m, to match Margot and make the equations more visually comparable? That's counter to the sources (Stern-Lev and Soter both use M), but not mathematically significant. Tbayboy (talk) 18:04, 31 January 2016 (UTC)

Yes, doing so would improve clarity. It may also be worth noting that the Stern-Levison criterion requires ejection to infinity, not just clearing of the orbital zone. Thank you for the great work on this article. JeanLucMargot (talk) 18:58, 31 January 2016 (UTC)

Infinity? I thought only Jupiter had enough mass to eject another body from the system. Their paper seems to me to indicate that the criterium is a deflection angle of 1 radian, not any particular distance. Does that imply infinity? Tbayboy (talk) 01:16, 2 February 2016 (UTC)

My apologies, I was mistaken. Levison based a similar orbit-clearing argument on Tremaine (1993), which does require ejection to infinity, but the Stern-Levison paper uses a slightly different approach. Please ignore my previous suggestion. JeanLucMargot (talk) 02:01, 2 February 2016 (UTC)

Where does 1.91e-4 come from (as opposed to 1.9e-4)? It is clear that we should note the origin of k in a footnote. --JorisvS (talk) 15:19, 5 February 2016 (UTC)

In the paper, equation 8, is an expression involving the main sequence life of the star. For the sun, he uses 10 Ga (or 1e10 years). So the value is (1e10/1.1e5)^(-0.75) (where ^ means "to the power of"). That expression evaluates to 1.91e-4. In equation 9, he does that substitution but rounds the printed value down to 1.9e-4. That rounding, however, changes Π for Earth from 812 (for 1.91) to 816 (for 1.9). Since Π=k for Earth in these units, as noted by Cuddlyopedia, and Margot published Earth's Π as 8.1e2 (812 rounded to 2 digits), the 816 stands out as contradictory since it rounds out to 8.2e2. To be consistent with his published Πs (and equation 8) we should use k=812. 816 is consistent with equation 9. Tbayboy (talk) 00:50, 6 February 2016 (UTC)

Instead of trying to understand how rounding affected the values, it may be simpler to calculate the value of k. One can show that $k=3^{\frac {1}{2}}C^{-{\frac {3}{2}}}(100t)^{\frac {3}{4}}{\frac {m}{M}}$, where $m$ is the mass of Earth, $M$ is the mass of the Sun, $C$ is the number of Hill radii to clear, and $t$ is the lifetime of the Sun on the main sequence in years. With the values in the paper ($C=2{\sqrt {3}}$ and $t=10^{10}$), one finds $k=806.85$ — Preceding unsigned comment added by JeanLucMargot (talk • contribs) 04:03, 9 February 2016 (UTC)

Well thank you! The 1.1e-5 is itself rounded... My main question now is how can we source it to your paper, at most using straightforward math to get there (i.e. how do we satisfy Wikipedia's WP:Verifiability criterion)? --JorisvS (talk) 20:26, 9 February 2016 (UTC)

I did not use the k formalism in the paper, so obviously there is no direct source for the correct k value. Perhaps the wikipedia article could state that, then provide the correct value for k (with or without the derivation). One way to verify the result is that the suggested k value does reproduce the values in Table 1 of the paper. JeanLucMargot (talk) 20:42, 9 February 2016 (UTC)

Without any direct and concrete derivation from sources, it would violate verifiability: "How can other people check that it is accurate?". We may be able to find something, though. We also know that $k={\frac {1}{{a}{C^{\frac {3}{2}}}}}$, with a the 1.9e-4 to within rounding, so if we can relate a to variables and constant that are clearly defined in the paper, that would already help a lot. Specifcally, if we can get from your paper that $a=3^{-{\frac {1}{2}}}(100t)^{-{\frac {3}{4}}}{\frac {M}{m}}$, we would have our derivation. --JorisvS (talk) 21:36, 9 February 2016 (UTC)

I also think the difference is due to the rounding to 1.1e5. I think that number is determinable from the paper, following the instructions there: substitute equations 1 and 5 and the stated period conversion into equation 6 and separate out the variables (getting eq.7). You can then carry it forward into eq.8 and get k as before. I think the 1.1e5 comes from ${\frac {\pi }{50\times 9^{\frac {1}{3}}{\sqrt {G}}}}$. I tried it and was way off, but I think my problem was the unit conversion for G from kg-m-s to earths-au-years. I'll give it another try on the weekend (using a program rather than a calculator), if nobody beats me to it.

Note: With k=806.85, Π for Haumea=7.8e-3 and Makemake=7.3e-3. Tbayboy (talk) 02:54, 10 February 2016 (UTC)

Where did you get that formula? --JorisvS (talk) 18:19, 10 February 2016 (UTC)

Um, as mentioned. All the a, m, and M terms were separated out (and I got the same for them as eq.7, so I might have done something right). If it looks wrong, it probably is, but it's just trying to follow what the paper does to get to eq.7. Tbayboy (talk) 00:07, 11 February 2016 (UTC)

Okay, I've now figured out what you did. It looks OK, but to be able to get to the 1.1e5, you have to still have to multiply this whole thing with M_Sun^5/6, M_Earth^−4/3, and 149597870700^3/2 m, not convert G to those units. That'll give you the constant in seconds, which can then be easily converted to years. This gives me 110948.922 yr. This gives 1.92239e-4 for the constant in equation (9), which in turn gives k = 806.81. Given the amount of calculation involved, I wouldn't be surprised if the minor difference between what I just found here and Margot's k above is simply due to numerical errors. Along similar lines, following the paper, the analytical value of k should be derivable, though it involves an enormous amount of bookkeeping. I expect to add this derivation to the article in a note later. --JorisvS (talk) 12:44, 11 February 2016 (UTC)

I've found that the difference between 806.81 and 806.85 is due to using a solar mass of 332946 Earth masses, yet calculating it from the stated kg values (1.98855e30 and 5.9722e24) gives 332967.75. Using the latter in Margot's above formula gives 806.81. Also, if I derive an expression for k following Margot's paper, the result look very different from Margot's result above, yet when used to calculate k, they give the exact same figure. --JorisvS (talk) 13:42, 11 February 2016 (UTC)

Thanks for pointing out the error. After correcting for it, I got similar values -- different in the 4th or 5th digit, but that's probably just due to different input value, like 365.25 days in a year, or to floating point arithmetic. In the end I got k=806.84; more precisely, 806.83nnn, but the nnn changed depending on the order of sub-calculation. Given the accuuracy of the inputs (especially 1e10), I think we can just use 807 for the page.

The expression I got for k at first looked a lot different from Margot's above, but I used the P-to-a conversion (kepler's 3rd) for converting the solar mass into G, pi, au, year (etc), combined like terms, then converted the remaining G, pi (etc) back in to solar mass, finally arriving at Margot's expression.

So we can derive the more exact k from the paper using high school algebra and following the instructions in the paper. Is that good enough for Wikipedia? Tbayboy (talk) 20:27, 14 February 2016 (UTC)

Thank you for how to convert that to Margot's expression. Yes, that's good enough for Wikipedia. --JorisvS (talk) 21:59, 14 February 2016 (UTC)

Okay, I've added it to the article. What has me thinking, is the ∝ in the expression for the main-sequence lifetime used to derive the expression for k; how accurate is it to simply have used = instead? --JorisvS (talk) 14:45, 24 February 2016 (UTC)

Wow, great work! I've updated the table numbers for the new k for Haumea and Makemake, and the Π=1 column -- no big changes, just a few dropping by one in the last used significant digit. The paper says that the star′s main sequence lifetime ″has uncertainties up to a factor of 2″ ″for most stars of interest″. I don′t know how much of that is due to the 5/2 power factor versus how much is the uncertainty of the Sun′s main-sequence lifetime. Tbayboy (talk) 17:10, 28 February 2016 (UTC)

Spelling?

While I am not arrogant enough to change the spelling to the American form (which appears several times both in the article and on this talk page), is there some historical basis for including the superfluous British 'u' in the title? Is that naming (and other) history worth mentioning in the article?

It's how the IAU spells it in the source for the term. It's a common and valid spelling, so it's not worth mentioning. That's not meant as an argument against changing it, just an explanation. Tbayboy (talk) 17:31, 10 February 2017 (UTC)

Totally vague

I wonder how the IAU defined the "neighbourhood" or "region" of a planet. Is it half an astronomical unit within the planet's center? Or 10.000 miles? 100.000 miles? 100.000 nautical miles? Since the IAU didn't concretize that the definition of "clearing the neighbourhood" is too vague to be taken seriously. And if Pluto and Eris were no planets according to that definition, so wouldn't be Earth, Mars or Jupiter. Complete nonsense which has nothing to do with whether a body is a planet or not. 212.186.7.232 (talk) 09:18, 31 March 2019 (UTC)

See Hill sphere. Ruslik_Zero 07:03, 1 April 2019 (UTC)

Then the third point should've been called "clearing the Hill sphere". Still, some of the eight other planets wouldn't be planets according to that definition. The nonsense with this is also that a planet that hasn't cleared whatever is considered a "dwarf planet" which presumptively assumes that the body is very small but that's not the case with Jupiter for example (a giant planet that would have to count as dwarf planet according to the IAU). But the IAU's definition is anyway wrong because planets don't have to orbit a star. A planet is any celestial body in hydrostatic equilibrium that's neither a star (including L- and T-type stars) nor a moon. 212.186.7.232 (talk) 05:52, 2 April 2019 (UTC)