Talk:Planet/Archive 3

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Pluto Randomness

Yahoo news just ran the following story that mentioned the Pluto controversy in regards to truthiness. I thought it was interesting, perhaps ironic. Of course it really doesn't change our discussion, but it humored me anyway. — Ram-Man ^{(comment) (talk)} 17:20, 28 August 2006 (UTC)

"Clearing its orbit"

How do Trojan Asteroids orbiting at the Lagrange-4 and Lagrange-5 points of a planet's orbit around the sun square with the definition of a planet that says that the planet has cleared its orbit? Banaticus 05:30, 1 September 2006 (UTC)

The small body is not in the planet's orbit. An orbit, in the pure sense is a simple 2 body ellipse, and this is what the planet must dominate and "clear". The small body at the lagrange L4 is not orbiting in that strict sense. Its path is different to the planet's, and there are two bodies acting on it. I know about this 09:39, 1 September 2006 (UTC)

Isn't Ceres still an asteroid?

I wasn't aware that Ceres's promotion to dwarf planet status meant that it was no longer an asteroid. It's still a member of the asteroid belt, last I checked. Serendipodous 22:24, 4 September 2006 (UTC)

Well, I believe that, according to the IAU, the term "asteroid" is now defunct. Asteroids, KBOs, SDOs etc all come under the class "small bodies".

That makes no sense. Materially, asteroids and KBOs are completely different things. Yes, they can all be small bodies, but there would need to be some kind of subgrouping to diffrentiate them. Serendipodous 17:08, 5 September 2006 (UTC)

Pluto is now asteroid 134340 http://www.space.com/scienceastronomy/060911_pluto_asteroidnumber.html yisraelasper

No, that just means it's a minor planet, not specifically an asteroidSerendipodous 15:17, 12 September 2006 (UTC)

Wasn't "dwarf planet" supposed to be the replacement for "minor planet"? — Rickyrab | Talk 22:34, 14 September 2006 (UTC)

Not exactly; "Minor planet" was split into two separate categories: "Dwarf planet" and "Small solar system body". Still seems to be following the same number system though. Serendipodous 22:38, 16 September 2006 (UTC)

Yeah, we'll have to wait and see whether dwarf planets have their number in their formal names.The Enlightened 23:38, 16 September 2006 (UTC)

Rocky versus Jovian planets and Star Metallicity?

I checked the link for reference (13) and it gave a summary of the article in Nature, although I did not directly read the source article in Nature itself. From what I could discern of it, it did not specifically preclude the formation of Jovian planets or Brown Dwarfs around metal-poor stars from the dynamics of the condensation of stellar nebulae, but it only noted that heavier terrestrial-like planets were precluded due to the simple lack of heavy elements in the initial nebula itself with metal-poor star formation. If Jovian planets and Brown Dwarfs are also clearly precluded from condensation dynamics, please give more references and change it back. - X (UTC)

Three-point versus four-point definition?

It seems to me that the Definition section could be cleaned up to clarify when it's referring to the four-point definition in the intro of the article, and when it's referring to the three-point definition in the Definition section. It tags the 'clearing the neighborhood' point as item (c), which it is in Definition though it's (d) in the intro. There seems to be a transition in this section at 'This resolution adds to a proposal...' where it's going to insert the fusion point, but it once again references 'clearing the neighborhood/orbit' as point (c), even though the intro inserts fusion at point (c). --Don Branson 12:31, 10 September 2006 (UTC)

Guys, coming up with your own definition is original research

If you can find another officially sanctioned definition, then fine. But don't just invent one off the top of your head. You're unlikely to come up with a definition that deals with all ambiguities anyway. Serendipodous 12:01, 13 September 2006 (UTC)

Guys, coming up with your own definition on the basis of official and widely known unofficial definitions is NOT original research

It is secondhand research, which is encyclopedic. Controversies stemming from religions have been handled quite well, so why not controversies between scientists and the general public? — Rickyrab | Talk 22:38, 14 September 2006 (UTC)

If you're going to give something as a second hand research it needs referencing. Besides, you're acting like the general public is in widespread opposition against the IAU, which is plainly not the case besides a few jokes by Stephen Colbert.192.17.229.43 00:15, 15 September 2006 (UTC)

We still have to wait. Dictionaries are not going to change instantly at least without saying there is a controversy. The IAU has set something in motion. yisraelasper

Duplication

This article needs to be condensed. There is no need for the two IAU planet definitions to be quoted in full twice. It makes the article confusing. I will try another form, and see if it works. If it doesn't, just revert it. Serendipodous 14:20, 15 September 2006 (UTC)

There. Done. Conveys exactly the same information but is 1kb shorter.

I think this article and "Definition of planet" are gradually becoming the same article

The overlap between them is growing by the day. It may be time to reconsider merging them. Serendipodous 17:54, 15 September 2006 (UTC)

Disagree I think that the planet article should be more about the nature/cultural impact of the planets rather than a terminology dispute. The basics should be covered here but another article is needed to cover the full controversy.70.225.161.247 04:37, 18 September 2006 (UTC)

Ice dwarf

This term does not mean what you think it means. Insofar as it is used at all, it refers to any of a number of icy bodies in trans-Neptunian space; it does not refer to a class of "dwarf planet". That is, it is a popular synonym for TNO. No term has yet been settled on for the class of "Pluto-like" object (in fact, none has been suggested since "Pluton" and "Plutonian object" were rejected).

Neither the term "ice dwarf" nor "Plutonian object" belong in this article. RandomCritic 13:16, 16 September 2006 (UTC)

Actually, "TNO" is a locational term, whereas "ice dwarf" is a compositional one. It's like the difference between "terrestrial planets" and "inner planets" - although the list may be the same they are *not* synonyms. Besides, I believe there are various rocky bodies out beyond Neptune that would not qualify as ice dwarfs. You are correct that there are "ice dwarfs" that are not dwarf planets, and I will modify the page accordingly. However, the term belongs in this article as much as "gas giant" (which also is not defined by the IAU).The Enlightened 23:32, 16 September 2006 (UTC)

Objection

I haven't followed closely enough this dispute over the "separate definitions" and "merged definition" to have much of an opinion about it, but I do object to mass reverts which delete contributions that other editors have made that have nothing to do with it. At the very least the reverter should have the courtesy to make sure that only the parts of the article he intends to revert are affected. RandomCritic 21:18, 17 September 2006 (UTC)

Yeah, I'm sorry. I had intended to go back and change those bits but forgot. I apologise. 192.17.229.43 21:40, 17 September 2006 (UTC)

Free-floating planemos

Correct me if I'm wrong, but if they're not orbiting a star then they do not satisfy the first criterion. Or is this supposed to mean the planemos are orbiting star clusters (and therefore orbiting many stars)? If so, it's worded badly. Either way, it's far too technical for an introductory paragraph. I'm removing it. _└ ^OzLawyer / _talk ^┐ 22:40, 17 September 2006 (UTC)

It seems to have been a very badly worded addition. I'll try to add the same information under criterion 1.The Enlightened 23:53, 17 September 2006 (UTC)

Clarifying & improving the definition

I felt a new section was needed to discuss the issue here. I think it should be mentioned that the "clearing the neighbourhood" criteria is considered to be a lower mass limit as an object needs to have a certain critical mass to achieve this. As such, "planets" that orbit stars outside our solar system will also have cleared their neighbourhood. I'm going to try to improve the definition for clarity's sake. Additionally, does anyone know why the IAU specifically excluded free-floating objects in young star clusters, but not in, say, old ones? The Enlightened 14:42, 19 September 2006 (UTC)

Additionally, free floating objects outside young star clusters were not excluded from any definition, but nor were they included. As such they belong in a separate "possible" class and have been listed as such. The Enlightened 15:07, 19 September 2006 (UTC)

The "clearing the neighbourhood" criteria might be considered a lower mass limit by you, but not necessarily by everyone else. There is no minimum mass that an object must theoretically have to be able to clear its orbit around a star. It all depends what else is there. So an object could've cleared the neighbourhood around its star, but be of greater mass than any object in the solar system that has done so. Therefore your version of the definition not only failed to make things clearer, it made things inaccurate. The reason why free-floating objects in young star clusters were excluded is that everyone on the working group agreed they were not planets. The argument was basically between those who thought planets should be defined by what and where they were (i.e. orbiting stars), and others who thought they should be defined by how they came into being - i.e. within protoplanetary discs. Free-floating objects in young star clusters wouldn't have had time to have both been formed and thrown out into interstellar space, so both groups could agree those weren't planets. Are you prepared to compromise on this at all? I've moved towards having a combined definition, which I'm not entirely happy with, but I can't see they you're prepared to move at all. Your new version is a lot longer and is no improvement. --Cuddlyopedia 16:11, 19 September 2006 (UTC)

As the problem seems to arise because of differing interpretations of the 2003 working definition on extrasolar planets, I think it advisable to deconstruct it to see what it actually says and doesn’t say. I apologise if this is somewhat lengthy.

The first thing to say is that the working group couldn’t agree on a definition of extrasolar planets. So they agreed to set out a position statement on those limited areas where they could agree. So they defined certain objects to be planets, and certain other objects not to be, and the rest they said nothing about. This was all cobbled together in something of a rush, which is why it is very badly drafted (and a lesson in how difficult it is to draft a consistent definition). It was first created in 2001, and the 2003 version is modified from that.

Criteria 1 in the working definition states:

"Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System."

The first sentence states that objects with masses below the fusion limit that happen to orbit stars are planets. It does not say that all planets orbit stars. Nor does it say that all planets have to have a mass below the fusion limit (although criteria 2 does). This first sentence does not give a minimum mass – considered in isolation, an object the size of a baseball orbiting a star would be a planet. However, the second sentence refers to a minimum mass for any object – a star-orbiting object or a non-star-orbiting object - to be a planet. The question is: What is the minimum mass for an object to be considered a planet in our solar system?

This is a question of interpretation. It must be a least the self-gravitationally-round mass. It doesn't say 'the smallest mass for objects that are considered planets' (i.e. the mass of Mercury). What other mass is there? The only other one is the minimum mass for an object in our solar system that enables it to clear the neighbourhood of its orbit. And how do we determine what that mass is? If we do it by observation, then we’re back to the mass of Mercury (the smallest object we can see has cleared its orbit). If we do it by theory – and I have no idea how to do that or what the answer is – then we have some mass that is either less than or equal to the self-gravitationally-round mass, or (more likely, perhaps) some mass bigger than that but less than or equal to that of Mercury (it can't be bigger than the mass of Mercury because we know Mercury's mass was sufficient to clear its orbit). So the minimum mass for an object to be a planet in our solar system is somewhere between the self-gravitationally-round mass and the mass of Mercury.

Whatever it is, this just gives us a mass, a number in kg (or whatever unit you prefer). The second sentence in criteria 1 says that that mass – in kg – is the minimum mass for any extrasolar object to be considered a planet. Note that the second sentence in criteria 1 does not say that every extra-solar planet – the star-orbital and the non-star-orbital ones - must have cleared the neighbourhood of its orbit (and what does that mean for non-star-orbital objects anyway?). Nor does it say that star-orbital planets around other stars must have cleared the neighbourhood of their orbits. It does not incorporate any other attribute that the minimum mass planet in our solar system happens to have - even if that attribute was what you used to identify what was the minimum mass planet in our solar system in the first place.

Criteria 3 states:

"Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate)." (This is pretty straightforward.)

So the working definition says:

Any object with a mass below the minimum mass for an object to be considered a planet in our solar system (which is somewhere between the self-gravitationally-round mass or the mass of Mercury) is not a planet.

Any object with a mass above the fusion limit is not a planet.

Any object with a mass between these two limits and orbiting a star or stellar remnant is a planet.

Any free floating object in a young stellar nursery is not a planet.

Any free floating object between the two mass limits and not in a young stellar nursery is undefined as a planet or not.

--Cuddlyopedia 21:10, 19 September 2006 (UTC), slightly edited 06:25, 20 September 2006 (UTC)

Okay, I haven't been following a lot of this, so forgive me if I'm missing something, but first off, if a criteria is "clearing the orbit", and people are reading that to mean something about a lower mass, well, um, the criteria is "clearing the orbit"--the definition I see now talks about both. If anything, it's one or the other (and, since we can't do original research, it's "clearing the orbit"). Second, the first criteria says planets have to orbit stars or stelar remnants. This does exclude all free-floating "planets". So what is this longer and longer definition trying to say they're not excluded? Just give the damn IAU definition modified with the earlier IAU statement about extra-solar planets and be done with it. This is all getting very original researchy and apparently wrong. _└ ^OzLawyer / _talk ^┐ 07:22, 20 September 2006 (UTC)

I ripped it up. You want to talk further about extra-solar planets or interstellar planets or whatever, put it in a later section of the article. This is an introduction and we can't be extrapolating and suggesting and expanding and questioning and yadda yadda yadda. Honestly, even the "orbit around a star or stellar remnants" is going further than we really should be. But the rest of that stuff was just ridicuous. _└ ^OzLawyer / _talk ^┐ 07:34, 20 September 2006 (UTC)

It's ridiculous in your opinion. Personally I think we should state the 2006 definition and the 2003 working definition seperately, but people want them combined, which I've gone along with. The problem is the 2006 definition is exhaustive for our solar system, but the 2003 one for extra-solar planets says that some objects are planets, some aren't and the rest aren't mentioned at all. Also, the 2006 definition has 'cleared the neighbourhood of its orbit', whereas the 2003 definition has 'must have the the same minimum mass/size as for a planet in our solar system, and these are not synonyms of each other. Therefore, merging the two is non-trivial. I'm open to suggestions as to how to improve the presentation of the article, but not to changes that are plainly wrong. --Cuddlyopedia 14:55, 20 September 2006 (UTC)

While not wanting to get into an angry debate about this, it appears to be ridiculous in most people's opinions except for your own. Just because we don't know the exact mass needed to "clear the orbit" doesn't mean the "clearing the orbit" criterion isn't the lower mass limit. We don't know exactly the mass needed to be self-rounded (and that also changes on other factors - the temperature and composition of the body) or the exact mass needed to fuse deuterium (which again can change depending on the metallicity of the body). The lower mass limit of planets in our solar system is the mass required to clear the orbit, whatever mass that may be. It doesn't need to be specified as a number. The definition we list should cover all those objects that the IAU has definitely included as planets - the eight in our solar system and the equivalent objects round other stars. We can then mention something about the objects that the IAU has not included or excluded, and list them as being of masses between deuterium-fusing size and "the lower mass limit above". I feel this is an appropriate compromise and, although its a bit long-winded, its logically clearer than the alternatives and it satisfies your desire to include the 'maybe' planets. In fact, I attempted something of the sort and it was reverted.The Enlightened 15:17, 20 September 2006 (UTC)

As I said above, I think even including the working definition is wrong, so I propose this (which will soundly be rejected by all): The definition at the top of the page is the IAU definition on planets in our solar system. Period. You can add a note that planets outside the solar system are discussed in section XX of the article. In that section you can go to town with the working definition, the possibility that something is or isn't a planet based on that working definition combined with "common sense" and the like. Original syntheses of already published material (something that doesn't naturally follow for all to see) is considered original research and cannot be included in a stated definition of fact on Wikipedia (which is what all of these attempted compromise definitions are doing). _└ ^OzLawyer / _talk ^┐ 15:46, 20 September 2006 (UTC)

Original syntheses of different pieces of work into something new is indeed original research. However, summaries of existing information is what wikipedia is all about. The first thing someone wants to know when they look up this page is "what is a planet?", not "what is the exact wording of the resolution about planets in our own solar system?" We need to cover the IAU's view of a planet in the intro for all planets, not just the 8 of the 250 that happen to be in our system. We should do it as succintly as possible, which was best done in the original four point summary. That intro was holding for a long time as acceptable to all until cuddlyopedia's objections. We should keep it, and then list details, specifics etc in the "definition" section. The Enlightened 16:24, 20 September 2006 (UTC)

"The lower mass limit of planets in our solar system is the mass required to clear the orbit, whatever mass that may be." Well that's your interpretation. POV. But even if I accepted it (which I don't), all the extrasolar planet working definition says is that an extrasolar planet must have at least that mass. It does not say that an object with that mass must clear its neighbourhood of its orbit around its star. You are confusing a property of an object (its mass) with the effect of that object due to its mass on other objects in its neighbourhood. Let's try a thought experiment: Assume that there is discovered an object in the outer solar system just bigger/more massive than Mercury (this is not implausible - Mike Brown for one speculates there may be objects bigger than Mars out there). Given the size of its orbit, it is highly likely that this object will not have cleared the neighbourhood of its orbit, and therefore would not be a planet but would be a dwarf planet in our solar system by the IAU's 2006 definition. (Indeed, one of the objections to the definition is that there may be dwarf planets bigger than some planets!) Now lets consider that very same object orbiting another star, but not having cleared the neighbourhood of its orbit, and ask whether it is an extrasolar planet by the 2003 working definition? Let's go through the criteria set out in that definition. Is its mass below the fusion limit? Yes. Is its mass sufficient to cause its gravity to force it to be nearly round? Yes. Is its mass above the lower mass limit for a planet in our solar system? Yes - its mass is bigger than Mercury, and the lower mass limit cannot be more than the mass of Mercury. So the object is a planet by the 2003 working definition! But by your version of the merged definition, it is not (because you require it to clear the neighbourhood of its orbit, which the 2003 working definition does not), which means that your version of the merged definition does not accurately summarise what the IAU has to say are extrasolar planets. And if it is inaccurate it has no place in Wikipedia. Now, unless you can fault the logic of my argument with chapter and verse relating to the actual wording of the two definitions, I suggest you concede that your merged definition was unfortunately not correct. We can then agree on a correct merged definition and sort out what goes where in the article. --Cuddlyopedia 2:30, 20 September 2006 (UTC)

I do understand your interpretation. I really do, and you just explained it very well. But I do think there is another interpretation, which I will try to explain. Let's just say the "clearing the orbit" criterion was never passed, and instead the original "lower mass limit" for our solar system was the "round from self-gravity". At the moment the smallest object in our system accepted for such a quality is Ceres. Now, imagine another system with a body made of other materials that was a lot closer to a hotter Sun. This would mean it would need a lot less mass than Ceres to be rounded by self-gravity, but, by your interpretation, would be under the lower mass limit for our solar system and would not count as a planet. Now, I don't think it is POV to say that, in such a case, scientists would have recognised such an object as being above the lower mass limit. That is because the mass limit for our solar system isn't an exact figure, but instead a lower mass limit that is dependent on other things. Had it been roundness it would have been associated with the internal structural forces and temperature of the object. As it clearing its path its associated with distance from the Sun, the nature of the rest of mass in its orbital path etc. In short, its not an exact set limit but a limit associated with a property, and one that can thus change depending on the other qualities that affect that property. This lower limit for mass of dwarf planets changes even within our own solar system. A Ceres-sized TNO wouldn't be round because it would be so much more solid due to colder temperatures. To say that the group devising the working definition meant that we should work out the size between the smallest planet and largest non-planet in our solar system (when such classes are based on properties) and then apply that mass to extrasolar planets regardless of properties is, frankly, ridiculous. They clearly did not mean that. Clearly. All they did mean was "well we don't want to preemptively make a statement on the lower size of planets because of the furore over our solar system, so we'll just set the upper limit and say "whatever the lower boundary associated with mass/size/volume/whatever in our solar system turns out to be, it'll be the same for extrasolar planets". They didn't know exactly what would be the lower boundary (though they certainly would have been aware of the possibilities) so they just said it in this vague way. They probably could have stated it more unambiguously, but they wouldn't have thought anyone would have misinterpreted what they meant. This isn't a POV interpretation, it's the reasonable obvious meaning when one considers the context of the debate. You were right about the ejected planets thing, and I was wrong not to include it previously, but I sincerely believe you are truly mistaken about this. The Enlightened 14:45, 21 September 2006 (UTC)

"All [the WGESP meant] was "well we don't want to preemptively make a statement on the lower size of planets because of the furore over our solar system, so we'll just set the upper limit and say "whatever the lower boundary associated with mass/size/volume/whatever in our solar system turns out to be, it'll be the same for extrasolar planets"." I agree with that, except that I do think they were thinking in terms of mass/size rather than 'whatever'. Remember, one of the principle reasons the WGESP could not come up with a universal definition was because of the arguments over so-called interstellar planets, and definitions in terms of orbital dynamics have no meaning for such objects. Unfortunately, the IAU Congress did indeed use orbital dynamics as a criteria for planets in our solar system! The WGESP could have drafted it more unambiguously, and I'm sure they didn't think anyone would interpret what they said differently to what they meant. But lawyers make fortunes on just such events all the time. It just goes to show how difficult it is to draft an unambiguous definition. I do understand your interpretation. I really do, and you just explained it very well. But I'm not insisting on my version of the merged definition over yours because I'm insisting on my interpretation over yours. I'm insisting on it because mine includes yours, whereas yours doesn't include mine. My version has 'minimum mass/size for a planet in our solar system' and 'if in our solar system has cleared the neighbourhood of its orbit' as two seperate criteria. If my interpretation is correct, this is accurate. If your interpretation is correct, this is redundant and the definition is not as concise as it could be, but it is still accurate. However, your version just has 'cleared the neighbourhood of its orbit' so if my interpretation is correct your version is innacurate. Faced with a choice between definitely accurate but possibly a bit over wordy, and concise but possibly wrong, I think we should err on the side of caution and go with my version. --Cuddlyopedia 08:00, 23 September 2006 (UTC)

"Original syntheses of different pieces of work into something new is indeed original research. However, summaries of existing information is what wikipedia is all about." - The Enlightened

The fact that you guys are arguing about how the two definitions can or can't be reconciled, and if they can, on what terms, shows exactly why this is not a summary but an original synthesis. Even if you two were to come to an agreement, as soon as someone else comes by and says "nu-uh, that's not what 'IAU statement X' says," you again see how this is original research. Really, it's not a simple summary and you both know it. _└ ^OzLawyer / _talk ^┐ 17:39, 21 September 2006 (UTC)

I think it counts as a fair summary. Both definitions say it must orbit a star (although it specifies which star in one). One definition says an upper mass limit which is above all objects covered in the other. And one definition says the lower limit is the same as in the other. If you look at the policy on original syntheses it explains this means you add sourced argument A to sourced argument B to advance new position C. There is no position C here, just sources A and B. Look at the example on the no original research page to see it means something very different. 70.225.161.247 18:22, 21 September 2006 (UTC)

That's because I had already made the changes by the time you looked. The definition before was an original synthesis. _└ ^OzLawyer / _talk ^┐ 22:37, 21 September 2006 (UTC)

I still don't believe my summary was a synthesis as such, and I think the new intro has info which is a little superfluous to be honest. However I'm acceptant of it if it keeps everyone happy - what I was really against was including the lengthy full resolution and working definition.The Enlightened 22:33, 23 September 2006 (UTC)

Actually, Osgoodelawyer, if you look above you'll see that I originally wanted the two definitions stated seperately, as I knew how difficult it can be to merge definitions without error. I later went with a merged definition in an attempt to get agreement, as most people seem to wish this. I'm happy with the introduction as changed by you, with one tiny, itsy-weeny caveat :). Perhaps we could say: "The IAU has not yet taken a position on whether objects of planetary mass that have been ejected from systems or which formed in interstellar space count as planets, except to exclude free-floating objects in young star clusters"? I won't make that change immediately to see if there is any objection. --Cuddlyopedia 08:25, 23 September 2006 (UTC)

Aren't "ejected planets" only physically possible in non-young star clusters? I thought interstellar planet in young star clusters just formed outside star systems (so therfore haven't been "ejected").70.225.171.73 17:08, 23 September 2006 (UTC)

Yes. Probably. I think we should be cautious about what the WGESP meant or its motivations behind its definition - rather we should just go with what they say. As they went to the trouble of using 1 out of 3 criteria to specifically rule out free-floating bodies in young star clusters, I think we should mention it somewhere in the introduction. I will wait until after the weekend, then if no objection will make the change. --Cuddlyopedia 07:00, 24 September 2006 (UTC)

Sorry to interrupt the technical discussion here,but can I give my thoughts as a complete layperson with an interest in astronomy? I have to tell you that astronomers are losing credibility here, and the more I read about the new definitions the worse it gets. First, under the new rules a dwarf planet is explicitly not a planet, which is confusing, and the name is stupid anyway (I now it's an analogy with stars, but please. Snow White and the seven Plutonians anyone? What's next - Elf Planets and Troll Planets?). Second, astronomers tell us Pluto doesn't make the grade as a planet because it's too small. Fair enough, I can see the logic and the public would come to accept it. But then I see under the new rules about 'clearing the orbit' that a 'dwarf planet' could in theory be bigger than Mercury. Hello? I don't care about the technical reasons, let me tell you now (& sorry about the capitals), but the public will NEVER EVER EVER accept this. If an object bigger than Mercury is discovered and they try to tell people that 'no actually it's still only a dwarf planet' then astronomers will lose all credibility. The public will start to think that you just make up the rules to suit yourselves. They'll think maybe that you just want to keep things nice and tidy with eight planets and don't want to deal with those messy KBO's and their nasty irregular orbits - just not clubbable. And this will be happening at the same time as astronomers are telling us about those amazing exoplanets that break all the rules (bigger than Jupiter on an irregular orbit as close as Mercury!) To put it mildly, there's a credibility problem.

Let me make it simple - SIZE MATTERS. What the public want is a definition that says anything above a certain size is a planet, anything below it is too small. Sorry if that causes a problem, but there it is. The strange thing is, it shouldn't be that hard should it?? Astronomers are the ones who made an analogy between dwarf stars and 'dwarf planets'. Forgive the crude explanation, but isn't the difference between a brown dwarf and a proper star the fact that a star is massive enough to generate nuclear explosions in its core? In other words, size matters. Can't astronomers follow the same logic through with planets? Surely there is some point where an object becomes massive enough to generate heat at its core. Sure a 'dwarf planet' is big enough to become a sphere, but that's about it. A planet should be big enough that the pressures and heat at its core generate activity - real geology like mountains and rift valleys, or else the weather and storms of the gas giants. OK a planet may be dead now like Mercury, but it did see action once. That's the difference between the smaller bodies and planets. Asteroids and 'dwarf planets' are just dead lumps of rock and/or ice orbiting the sun. They have no real life of their own - the only reaction is to the sun's effects, even if it is spectacular like comets. But planets are big enough to generate their own activity - they are WORLDS in their own right. They have landscapes and formations shaped as much by themselves as by the sun. People are fascinated by that and that is why they care about the definition of a planet. There are always going to be borderline cases with any definition, but people will only accept anomalies if there is a clear reason for it. Frankly this whole thing about clearing the orbit isn't clear enough. It should probably be dropped if it causes so many problems. People want a clear simple definition based on the properties of the object itself, not some suspiciously complicated scheme based on its relation to other objects. Neelmack 12:55, 19 November 2006 (UTC)

Wow. Quite the rant there. :-).

OK. First of all, not everyone (I would take a shot and the dark and say virtually no one) who edits the astronomical articles on Wikipedia is a professional astronomer. I certainly am not (I have a Masters in early modern textual scholarship, which is about as far from planets as you could get), so there's no point in shouting "you" at your fellow reviewers. Also, not all astronomers agree with the current definition, so whether they will lose credibility depends on how this fiasco is ultimately resolved. Thirdly, the term "dwarf" has (as you yourself noted later in your comment) a long history in astronomy and beyond it; there are dwarf stars and also dwarf galaxies. People formerly called midgets now prefer to be called dwarfs. Should we tell them that they should just as well be called elves and trolls? So. In astronomy there are dwarf planets and there are dwarf stars. But the difference between dwarf stars and dwarf planets, as Dava Sobel pointed out, is that dwarf stars are still stars, whereas dwarf planets are not planets. Therein lies the problem, and the most obvious road to compromise. Keep the three-tier system of planet/dwarf planet/small solar system body but make dwarf planet a subset of planet. This prevents schoolkids from having to memorise the hundreds of future additions soon to flood our consciousness and also keeps the planetary scientists happy.

As to the public never accepting the orbital dominance criterion; first of all, I doubt the public is even aware of the whole debate. The only thing most people understand of all this fracas is that Pluto is no longer a planet. Also, the chances of anyone finding a dwarf planet larger than Mercury are, by this definition, fairly miniscule. To be larger than Mercury, a new dwarf planet would have to be more than 22 times the mass of Eris or, to put it another way, as many times larger than Eris as Eris is larger than Ceres. Also, to be a dwarf planet, such a world must exist in a region of space populated by objects not much smaller. Given the size distribution of objects in the Kuiper belt, this region would have to be gigantic; hundreds of times the size of the Kuiper belt, just as the Kuiper belt is hundreds of times the size of the asteroid belt. Such a region may well exist somewhere, but very very far away, in an orbit large enough to hold it. If it is out there, we're not likely to find it any time soon, if ever. Serendipodous 15:04, 19 November 2006 (UTC)

It wasn't meant as a rant, more as an appeal, but ok the black and white print makes things look very stark. Point also taken about use of 'you'. My point about the name 'dwarf planet' is really that schoolkids will probably find the name funny, however immature we may think that, and have a lower opinion of astronomy as a result. I was thinking about them making jokes about the Snow White/Lord of the Rings type of dwarf, but if they make jokes about real people, isn't that more of a reason to be concerned? Anyway, whatever, maybe I'm over-reacting and there's nothing to worry about. As you say, the whole thing depends on how the definition 'fiasco' is resolved. What you say about people not understanding about 'clearing the orbit' is precisely my point. All people want to understand is a definition based on size, and by size I mean diameter, not even mass. There is also the fact that people in the future,(the schoolkids I mentioned) will at least know of the existence of the orbital dominance criterion, because they will be taught that that is what distinguishes a 'dwarf planet' from a real planet. But I am reassured by your comments about anomalies being very unlikely, so maybe that won't be a problem either. My basic concern is that the word 'planet' is more than just a scientific term to people, and astronomers need to be aware that they have to balance proper scientific criteria with the perceptions of people, if they are to avoid the public turning away from 'popular' astronomy in confusion and disillusionment. Neelmack 20:13, 23 November 2006 (UTC)Neelmack

Pluto's atmosphere

From [[1]] "Pluto has an envelope of gas that surrounds it that grows as it approaches the sun and shrinks as it moves farther away, just as a comet's coma does. This is what is referred to as its "atmosphere." From [[2]] "Pluto's atmosphere... is extremely tenuous, the surface pressure being only a few microbars. Pluto's atmosphere may exist as a gas only when Pluto is near its perihelion; for the majority of Pluto's long year, the atmospheric gases are frozen into ice." Seeing that for the majority of its year it is in solid form, and the same applies to comets, I think this qualifies as "no atmosphere" for table purposes.192.17.228.233 23:34, 25 September 2006 (UTC)

• I disagree, and it should be noted that the atmosphere in 2002 was THICKER than it was in 1989. put it back up in the table.

Please reference your claims and sign your comments. "I disagree" written anonymously isn't enough I'm afraid. 192.17.228.233 02:53, 26 September 2006 (UTC)

GA Re-Review and In-line citations

Note: This article has a small number of in-line citations for an article of its size and currently would not pass criteria 2b.
Members of the Wikipedia:WikiProject Good articles are in the process of doing a re-review of current Good Article listings to ensure compliance with the standards of the Good Article Criteria. (Discussion of the changes and re-review can be found here). A significant change to the GA criteria is the mandatory use of some sort of in-line citation (In accordance to WP:CITE) to be used in order for an article to pass the verification and reference criteria. It is recommended that the article's editors take a look at the inclusion of in-line citations as well as how the article stacks up against the rest of the Good Article criteria. GA reviewers will give you at least a week's time from the date of this notice to work on the in-line citations before doing a full re-review and deciding if the article still merits being considered a Good Article or would need to be de-listed. If you have any questions, please don't hesitate to contact us on the Good Article project talk page or you may contact me personally. On behalf of the Good Articles Project, I want to thank you for all the time and effort that you have put into working on this article and improving the overall quality of the Wikipedia project. Agne 00:42, 26 September 2006 (UTC)

Actually, there was a GA dispute open on this page anyway :/. Homestarmy 13:47, 27 September 2006 (UTC)

Delisted GA Review

As per the GA review opened on this article, it has been delisted, for a combination of organizational issues, and because two sections have no references at all, namely, the history and the attributes of planets sections are pretty much not referenced. Review archived at Wikipedia:Good articles/Disputes/Archive 6. Homestarmy 13:47, 27 September 2006 (UTC)

How's it looking?

I've just reworked the history section to make it flow a little better. I actually think we've all done a really great job on this page, even it got delisted as a good article. Let's see if we can improve the references and do anything else that is needed to get it back on the list. The Enlightened 01:42, 12 October 2006 (UTC)

The lead section

The lead section is up for discussion... I made a change a few days back to address what I thought was a missing element, where we were just going straight into the IAU issue without giving any context. The new lead, incorporating elements from the etymology section, reads as follows:

"The word "planet" originates with the Greek term "πλανήτης" (planētēs), meaning "wanderer". It has been used for thousands of years to refer to astronomical bodies orbiting the Sun, and more recently around other stars. However, prior to the 2006 adoption of an official definition by the International Astronomical Union (IAU), there was no formal definition of what constituted a "planet". The resolution adopted by the IAU states that, within the Solar System, a planet is a celestial body that..." (it continues with the IAU definition)

The older version, immediately prior to this, read as follows:

"Prior to the adoption of the 2006 definition by the International Astronomical Union (IAU), there was no formal definition of what constituted a planet. The definition adopted by the IAU states that, within the Solar System, a planet is a celestial body that..."

I feel that the old version had a very abrupt beginning, whereas the new one gives a better setup and better prepares the reader - especially those who aren't astronomy buffs - for the significance of the IAU decision. Otherwise, it feels like we're just rehashing the definition article. The Enlightened disagreed with the change, which is fine - but chose to revert tonight to a much earlier version. I'd rather discuss the matter first, even if it means restoring the version of the lead paragraph from just before my changes while we discuss, but I'm not comfortable with throwing away all of the progress prior to that point as it also removes changes and refinements from several other editors. I'd also prefer to quickly get a sense of whether people want to roll things back and then discuss, or discuss it as it currently is (with the new version in place) before things get reverted and re-reverted. Thoughts? --Ckatz^chat_spy

I'm aware of the issue some people have with the "context" of the definition but the previous introduction was a compromise that took a long time betwee numerous editors who had a lot of problems with the previous version. The new one made by David Kernow brought back a lot of these problems. The introduction is not the place for a chronological history of the meaning of planet - that is for a section in the article proper, which has been done very well IMHO. The first thing that should be done is to describe how the term is presently defined. Originally the wording was just "A planet is officially defined as (IAU definition)" but this was changed by anti-IAU people as "A planet is (very vague definition)... but in 2006, a resolution was passed..." After arguments that the introduction should not be a chronology were accepted by the anti-IAU crowd it was an acceptable compromise to change "A planet is officially defined as...." to "The IAU, the official body for these things, defines a planet as..." and then mention this is a new definition and that there was not one previously towards the end of the paragraph. A compromise as some felt such mentions weren't needed at all in the introduction. This remained stable for a long time. Additional problems were that some people (myself included) wished to see a combined definition of solar and extrasolar planets in a neat four point definition, but as some others argued that the "minimum mass/size" limit does not apply to the clearing the orbit criterion it was an accepted compromise to break it into two sets of bullet points, albeit in one extended definition. This also has been undone. Finally, it is the purpose of an introduction to define the term in all circumstances (both solar and extrasolar) before giving prominent examples (the big eight and the extrasolar 200). Finally, with the explanation that there was no previous definition towards the end there was a suitable place to mention there have been numerous historic planets, including Ceres and Pluto - something which we agreed to put in for the Plutophiles. This has also been removed. So in short, the previous introduction was flowing prose, sensibly ordered and addressed everyone's concerns. The new one does none of these things, and it should be reverted. The Enlightened 09:41, 23 October 2006 (UTC)

I just reread your post again, and I agree, the version before yours was very abrupt. However the one that existed until a few days ago did not have that problem, and did not need your contextualising. I can't see any improvement between that "original" version, and any version since.

And for the record the "several" editors participating in the progress before your edits totalled one: David Kernow. And it was his changes I mainly had the problem with. The Enlightened 14:38, 24 October 2006 (UTC)

Adding context helps, and makes it sound more encyclopedic, IMHO. So far, though, none of the regulars (the two of us excepted, of course) have commented. I'll put out a note later tonight asking for input, since it has been quiet on this page over the past few days. --Ckatz^chat_spy 15:59, 24 October 2006 (UTC)

As a rule, I'm not fond of repetition; indeed, I made the "History" and "Etymology" sections out of scattered paragraphs throughout this article mainly to get rid of it. Still, I agree that a better flow is required for the opening paragraph; all that's needed is a little creativity and we can find one. Serendipodous 16:03, 24 October 2006 (UTC)

I would agree that the history of the definition belongs in its own article section, further below. Child of Albion 13:53, 25 October 2006 (UTC)

Indeed, and the history and etymology sections work extremely well as the lead in to the main article. As for the introduction, I think the original was the best flow by far:

The International Astronomical Union (IAU), the official scientific body for astronomical nomenclature, currently defines "planet" as a celestial body that, within the Solar System,

(a) is in orbit around the Sun;

(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape; and

(c) has cleared the neighbourhood around its orbit;

or within another system,

(i) is in orbit around a star or stellar remnants;

(ii) has a mass below the limiting mass for thermonuclear fusion of deuterium; and

(iii) is above the minimum mass/size requirement for planetary status in the Solar System.

It does the first thing an introduction should do: define the present term, and it does this in a clear coherent and flowing way. It took a long time to get the first paragraph and the next few to this desirable state, and everyone was happy with it. Then David Kernow, in good faith, I'm sure amended it in order to class solar and extrasolar definitions separately and with other information of solar and extrasolar. I understand why, but it is better organised for both parts of the definition to be first. The long and winding story of how this definition came about should be addressed in the etymology, history and definition paragraphs further down. The Enlightened 00:30, 25 October 2006 (UTC)

I like the current introduction, but feel that it could do with have a "snappy" sentance before it. How about something like

"A planet is a large astronomical object that orbits a star. The International Astronomical Union ..."

(I'm not happy with the "astronomical object" here, but can't think of a better term) Bluap 22:05, 27 October 2006 (UTC)

I like your snappy sentence idea, although I vote for:

"A planet is an astronomical object that orbits a star. The International Astronomical Union currently defines "planet" as a ..."

Large is relative (especially in an article dealing with astronomy). I also feel that defining the IAU kills the flow. If a wiki-link is provided for the International Astronomical Union, I feel the context is enough for the reader to understand that the IAU is responsible for defining & naming. Plus, readers can always click the link to find out more...

--Benwildeboer 22:40, 27 October 2006 (UTC)

But that then suggests that any object orbiting a star is a planet. You would have to put in "a planet is a type of astronomical object that orbits a star." And as you can see further down, some scientists reckon planemos that have been ejected from a system count as planets. So then you have "a planet is a type of astronomical object." Seems pretty superfluous to me. Why not just say how its officially defined? The Enlightened 00:56, 28 October 2006 (UTC)

OK...upon re-examining the opening, I agree that it should jump right to the IAU definition. Can we not define what the IAU in the first line though? To me it hurts the focus of the section. --Benwildeboer 02:18, 28 October 2006 (UTC)

Yeah, I can see your point. That opening line has got very wordy. If I recall correctly it was to satisfy lots of points of view. Originally we had "The IAU officially defines a planet as.." but a lot of people hanging around immediately after Pluto's demotion claimed the definition wasn't a universal official definition, so it got changed to "The IAU, the official body for astronomical nomenclature, defines a planet as..." because a lot of people wanted to show that the IAU wasn't just one random astronomy body but the official thing for these things. Then those arguing that Pluto was a cultural planet wanted to make it clear that the IAU was only official for "scientific" definitions so that got put in. Then those who contested the extrasolar working definition wanted "currently" in there. Looking back now, I think it is still dodgy to say it is an "official definition" so I think we should keep that rough description of the IAU, but "scientific" is superfluous as astronomy is by definition science (rather than astrology). "Currently" is also unneeded as theres a bit about the working definition below now. I'll make these changes now. What do you think? The Enlightened 13:49, 28 October 2006 (UTC)

I agree that "Large" is relative. However, having the word in a snappy initial paragraph leads in well to the IAU definition of precisely how large an object needs to be, in order to be classified as a planet. Bluap 16:34, 28 October 2006 (UTC)

Well "medium" would actually be a more accurate term, seeing that brown dwarfs and stars are larger (both of which can orbit larger stars). So we have the sentence "A planet is a medium-sized astronomical object. Is there really much point? The Enlightened 16:49, 28 October 2006 (UTC)

"Solar system"

From the American Heritage Dictionary: solar system n.

1) (often Solar System) The sun together with the nine planets and all other celestial bodies that orbit the sun.

2) A system of planets or other bodies orbiting another star.

Thus using the term "The Solar System" is unclear when we are also discussing other solar systems also. 144.32.196.4 20:56, 27 October 2006 (UTC)

I'm not sure whats the correct term, but can the people that believe we should only use "solar system" to refer to the one we're in please argue their case here? The Enlightened 01:08, 28 October 2006 (UTC)

"Solar" is an adjective used to refer to the Sun. It is based on the Latin name for the Sun, "Sol". Both "Sol" and "Sun" are names for the star which Earth revolves around. Other systems of stars and planets would be called after the name of the star; the "Barnard system", the "Alpha Centauri system", etc. (not to say there are necessarily planets around those stars). Generically, it is called a planetary system. The term extrasolar planet makes it clear that it is not Solar. _└ ^OzLawyer / _talk ^┐ 13:48, 28 October 2006 (UTC)

Ok, I'm convinced. What's the generic name for a set of objects that orbit a star then? "Stellar system" and "star system" both refer to a set of stars in a cluster. The Enlightened 13:52, 28 October 2006 (UTC)

Planetary system (which I always thought referred to a planet and its satellites, but apparently it does not). _└ ^OzLawyer / _talk ^┐ 13:53, 28 October 2006 (UTC)

Technically, that isn't true. "Planetary system" only applies to the substellar material in orbit around a star, not to the star and the planetary system together. There is, as yet, no agreed generic term for what we call a "solar system." Serendipodous 10:35, 29 October 2006 (UTC)

planet rotation

I have a question. Do you know what causes planets to rotate?

This page is for discussing improvements to the wikipedia article, not for homework questions. You'd be best off searching on google for "planet rotation" or something similar. Thanks. The Enlightened 13:47, 29 October 2006 (UTC)

Easy tiger. He has a point. Should we mention it? Serendipodous 14:54, 29 October 2006 (UTC)

Definitely worth mentioning somewhere - if it's too specific for this article, it could certainly go in Planet or another similar article. (That way, we can suggest that people search Wikipedia for the answer...) --Ckatz^chat_spy 18:21, 29 October 2006 (UTC)

Um, this is Planet. Serendipodous 18:58, 29 October 2006 (UTC)

Ummm... just testing to see if you're paying attention? Oh good, you are, you pass, hooray, way to go, sheepish grin, thanks for catching that... thought I was at Solar System! --Ckatz^chat_spy 22:00, 29 October 2006 (UTC)

Historical planets

The table for "historical planets" included Eris, for some reason. I have removed it, as I cannot recall any point in time when Eris was officially considered to be a planet. (Speculation by the discovery team doesn't count - and the discussion prior to Pluto's recategorization was about changing from 9 to 12, or 9 to 8 - not 10 to 12 etc.) If there's a valid citation, then it should be brought forward. --Ckatz^chat_spy 21:57, 29 October 2006 (UTC)

The whole "tenth planet" malarky was started by this NASA article. Because it was an official NASA source, people started claiming that Eris was planet ten. Serendipodous 10:59, 30 October 2006 (UTC)

Well yes, I don't think its an overstatement to say that it was accepted culturally, at least for a while there, as the tenth planet. I had just found this [3] before I checked here, it seems to be the same press release. It's important to note that before 2006, Pluto was the only object ever "officially" accepted as a planet. All the planets up to that point got accepted by scientific consensus. In the absence of any information coming from the IAU, who were dragging their feet as they didn't want to pre-empt their work on a new definition (which was initially going to accept Eris!), scientists did go ahead and accept the then 2003 UB 313 as a planet. NASA's acceptance of this shows this and should be listed as such. Eris was certainly more accepted than the asteroids after #5.

Secondly, I would like to change back the notes on Pluto. We already have the reasons and such for Pluto's demotion in the above paragraph, and the table would be a mess if we included reasons for every object's change of category. We should just have notes about the level of acceptance. Perhaps "Officially accepted as a planet by IAU for this period, although disputed from 1990 onwards." The Enlightened 15:51, 30 October 2006 (UTC)

Seeing that there has been no reply to this, and that Eris held a similar position to the later asteroids I'm adding it back into the table with a note that it was not officially accepted. The Enlightened 18:36, 31 October 2006 (UTC)

Hold on please... there's no basis for adding such a claim. --Ckatz^chat_spy 18:38, 31 October 2006 (UTC)

If you're going to add Eris, you might as well add Charon and Ceres as well, since as soon as the draft proposal was released, everyone started calling them planets (assuming that the draft proposal would end up being the final decision). In addition, if Eris held a similar position to the later asteroids, so did Sedna, which I'm pretty sure I recall being called a planet when it was first discovered. _└ ^OzLawyer / _talk ^┐ 18:42, 31 October 2006 (UTC)

The important question here is how did scientific community refer to these objects. The media and amateur astronomers don't count - its professional opinion that does. That's why the later asteroids are in there, and thats why Eris should be. Science works by scholarly consensus and if a majority of scientists accepts something as the case, thats what the present scientific understanding is. Of course, if an official body then makes a definitive statement one way or another it trumps all this. But in the absence of any such statement regarding Eris, scholarly opinion did largely conclude it was a planet. The Enlightened 19:10, 31 October 2006 (UTC)

Are you sure? Scholarly opinion was moving away from Pluto being a planet, so why would it have accepted Eris as one? Note that scholarly opinion, and scholarly opinion that people hear about may be different. _└ ^OzLawyer / _talk ^┐ 19:14, 31 October 2006 (UTC)

Further to this, I think that there would have been a lot of talk about such a change. If the professional opinion really was one of acceptance (and we would need some pretty hefty citations to back this up), there's no way that it would have just "slipped by" unnoticed. --Ckatz^chat_spy 19:20, 31 October 2006 (UTC)

Quoting Mike Brown, 'Whenever you've discovered a new object, the first question your colleagues ask is "Is it larger than Pluto?" If you say, "no, half the size", like Quaoar, or "three quarters the size", like Sedna, they reply "not a planet then, huh?" When you say "YES!", however, as we did after 2003 UB313, people say "Great! The 10th planet has been found!" or something to that effect' Although scholarly opinion was definitely moving away from counting Pluto as a planet, doesn't mean it had entirely moved at that point. I don't think that the majority really had backed Eris as a planet, but there was undoubtedly a big chunk that had. In which case I think it should just be listed with a "partially accepted" note. The Enlightened 19:38, 31 October 2006 (UTC)

Meh, I've simply removed the other partially accepted asteroids. Looks better as a smaller box anyway. The Enlightened 19:50, 31 October 2006 (UTC)

As I see it, by listing Eris because it was "partially accepted" by the scientific community (even though the IAU did not recognize it as a planet), we open up the possibility of another "Pluto problem". While the IAU doesn't define Pluto as a planet, some scientists still do, including the head of the New Horizons mission. Do we then have to qualify the "2006" delisting? --Ckatz^chat_spy 20:08, 31 October 2006 (UTC)

Well, my argument was that the views of the scientific community matters, but only in the absence of official definitions. Anyway, this is easily solved by only listing planets that were fully accepted, officially or otherwise. The Enlightened 20:11, 31 October 2006 (UTC)

Actually, you'd have to add up to about the first 5 to 9 asteroids discovered, since it was only at around then that the definition changed to exclude asteroids. Adam Cuerden ^talk 03:05, 30 November 2006 (UTC)

References

Can we have a joint effort to go through the article and place references in? I'm going to try and do this over the next few days but help would be much appreciated! The Enlightened 03:03, 1 November 2006 (UTC)

Non Creationist planet formation models are highly speculative

I believe it should be stated in the article more forcefully that non creationist are highly speculative and do not have a very good track record. I cite the following in support: “... most every prediction by theorists about planetary formation has been wrong.” Scott Tremaine, as quoted by Richard A. Kerr who was proposing a new planetary formation model, “Jupiters Like Our Own Await Planet Hunters,” Science, Vol. 295, 25 January 2002, p. 605. [4] I also cite the following: “We cannot even show convincingly how galaxies, stars, planets, and life arose in the present universe.” Michael Rowan-Robinson, “Review of the Accidental Universe,” New Scientist, Vol. 97, 20 January 1983, p. 186. [5] 136.183.154.15 02:37, 29 November 2006 (UTC)

That's nice. —Joseph/N328KF (Talk) 02:38, 29 November 2006 (UTC)

This is a scientific article. It deals with the scientific models. Creationism is not scientific, ergo, it doesn't belong in this article. If you wish to drag this argument out further by demanding a definition of "scientific," I'd suggest you look it up first. Serendipodous 03:05, 29 November 2006 (UTC)

I would remind Serendipodous that 5% of American scientist are creationist. Although creationism is a minority view a number of respected scientist adhere to it. 136.183.154.15 03:24, 29 November 2006 (UTC)

Creationism invokes the miraculous. Miracles, by definition, cannot be measured, quantified or analysed. The world could very well have been created ten thousand years ago (or, for that matter, ten seconds ago) by a miraculous act, and anyone, including a scientist, is free to believe that if he or she wishes, but there is absolutely no way anyone could possibly prove or disprove it. Since miracles can do anything, they can explain any evidence at all, positive or negative. Science goes where the evidence leads, and the evidence, so far, has led science in the direction outlined in this article. Since this is, as I said above, a scientific article, it describes the scientifically derived theory for planetary formation. Discussion of non-scientific ideas belongs in articles on philosophy or theology, not science. Serendipodous 03:36, 29 November 2006 (UTC)

Ignore the troll, Serendipodous. This will go nowhere. —Joseph/N328KF (Talk) 03:38, 29 November 2006 (UTC)

Joseph, I would appreciate it if you could be more polite. Expressing a minority view is not trolling. Plus I believe the quote by Scott Tremaine demonstrates that past planet formation models by non creationist have a very poor track record. 136.183.154.15 03:43, 29 November 2006 (UTC)

Scientific models may be speculative, but they are still scientific, based on the observed physical evidence. That they may be speculative is no reason to place them on par with non-scientific concepts. Serendipodous 03:53, 29 November 2006 (UTC)

This is banned user "kdbuffalo" attempting to evade his ban. This address is likely to be blocked, but he may use others. --Robert Stevens 09:55, 29 November 2006 (UTC)

Historical Planet Table

Frankly, this is simply wrong: You'd have to add at least 5 Astraea to the list as well, and it would be very difficult to say for certain where you should stop adding asteroids. Adam Cuerden ^talk 00:15, 12 December 2006 (UTC)

Stating that the information listed is "simply wrong" without sources is quite the assertion. In First Steps to Astronomy and Geography (1828) by Hatchard & Son the first four asteroids are clearly listed as planets. Astronomers were aware these objects were somewhat different than the standard planets but still listed them as such. However, when more started turning up again in the 1840s (including Astraea) none of the new objects were fully listed as such. In the Berliner Astronomisches Jahrbuch of 1854 the asteroids Astraea through Eunomia were listed separately to the pre-1810 planets. It wasn't til 1867 that Ceres through Vesta were listed separately. The rest of the asteroids were not accepted any more than Eris was. i.e. Their status was left on hold while the definition of terms were cleared up. The Enlightened 21:32, 15 December 2006 (UTC)

Aside from that, changed "2006" to "present". Save everyone updating this each year - 2007, 2008, 43976, etc.martianlostinspace 15:13, 15 December 2006 (UTC)

Planetary spacing

(Seems kind of weird for the article not to mention Bode or Planetary spacing.)

There are no good, generally accepted explanations for the spacing of the planets in the solar system.

The Titius-Bode law (0.4 + 0.3 * 2(n-2) AU) works amazingly well, up through Neptune. It is empirical, an exercise in trying to come up with a simple formula dating back to about 1750, without much of a theoretical basis.

If the goal is a rough mental model of the planet spacing, there are two sets of planets:

The Inner Planets
Mercury Venus Earth Mars
0.4  0.7  1.0  1.5
  
The Outer Planets
Jupiter Saturn Uranus Neptune (Pluto)
5  10  19  30  39

Each set is spaced quite evenly. The inner planets are spaced at about 0.3 astronomical units. The outer planets are spaced at about 10 AU. The key mental concept is that the four inner planets are closely spaced, and the outer planets are spaced about 30 times farther apart.

Planet	Titius-Bode prediction	Real distance	Simple mental model
Mercury	0.4	0.39	0.4
Venus	0.7	0.72	0.7
Earth	1.0	1.00	1.0
Mars	1.6	1.52	(1.3)
(Ceres)	2.8	2.77	asteroids
Jupiter	5.2	5.20	(--)
Saturn	10.0	9.54	10
Uranus	19.6	19.2	20
Neptune	(38.8)	30.06	30
(Pluto)	(77.2)	39.44	40

The Titus-Bode law is not really respected in astrophysics. There is no explanational basis for it, and very little evidence that it works. The success of a scientific model is dependent on its predictions beyond what is already known - where the titus-bode "law" falls down. Any half-competent mathematician could come up for a formula that fits a set of eight known numbers. It's not worthy of inclusion in this article. The Enlightened 00:46, 17 February 2007 (UTC)

Additional Resources

• http://en.wikipedia.org/wiki/Titius-Bode_law
• http://en.wikipedia.org/wiki/Planet
• Bode's law - with some modifications for the outer planets
• The Original Solar System - Theory that the solar system had many more planets

---
What is the best simple mental model of the planet sizes?

Mercury, Venus and Mars are "a little smaller" than Earth (0.4 to .95 diameter). Jupiter and Saturn are "about ten times" (11 and 9 times dia). Uranus and Neptune are 4 times bigger. Pluto is one-fifth dia. (The difference in masses is greater than the difference in diameters.) The Sun is 100 times the dia of Earth. The distance from the Earth to the Sun is about 100 times the dia of the Sun. The solar system is almost all empty space -- the sun is small compared to the distances between, and everything else is extremely small.--69.87.199.195 14:24, 6 February 2007 (UTC)

There are three problems with Bode's Law. First, there's no scientific theory which explains it, second, it doesn't work for either Neptune or Eris, and third, there's no evidence that any analogous law applies to other systems. Serendipodous 09:41, 17 February 2007 (UTC)

What needs to be done to get this article up to spec?

This article seems to have gone into hibernation but it (and a number of other solar system articles) have been rotting in limbo for months. This is an important topic and needs to be addressed. So I thought I might bang some heads together and ask, what needs to be done? Serendipodous 14:39, 12 March 2007 (UTC)

I agree, this is indeed an important topic, and it could use some improvement. As to what, exactly, needs to be done... I think we should proofread this and correct all the grammatical and/or spelling errors we find, especcially ones that confuse and distract. Also, I think it might be a good idea to add some more information about the individual planets. And perhaps we should change the main title to "planets" instead of "planet"? Because it seems to me that this article refers more to multiple planets and to the definition of a planet rather than to one single planet. Any thoughts? Vsst 05:44, 21 March 2007 (UTC)

Edit

I have rearranged and rewritten the second paragraph in this article, and moved and edited a sentance from the first paragraph to the second. The second paragraph was confusing; although you could interpret what it meant. My rewrite is, I think, an improvement, but it is nowhere near perfect, obviously. I think this article could do with some more information and explaination about the topic covered in the second paragraph. Vsst 03:05, 27 March 2007 (UTC)

I'm afraid I don't get your edit. The 2006 definition doesn't actually do anything about the 200 extrasolar planets. It only applies to our solar system. I'm reverting it. Serendipodous 06:44, 27 March 2007 (UTC)

Ok, I just reread my original edit and the current version of the paragraph. I agree with you, the 2006 only applies to our solar system. The current version is much better. Vsst 02:55, 29 March 2007 (UTC)

Intro

The intro to this article is much too focused on the definition of a planet. While this is obviously an interesting subject now, it would be better as its own subsection. The intro should instead briefly define "planet" without using a bulleted list, then mention the major points discussed in the article. See WP:LEAD. Gnixon 05:07, 28 March 2007 (UTC)

How should the intro define planet, though? It's not possible to briefly define planet. I tried to fix the definition in this article's lead an it turned into a separate article. Serendipodous 06:28, 28 March 2007 (UTC)

Almost exactly as it is in the first two paragraphs, but bringing the list in-line. The last two paragraphs aren't appropriate for the intro. The recent IAU debates should be mentioned in the intro, but so should the other topics covered in the article. Remember, the article isn't called "IAU definition of planet." The text in the first two paragraphs explains the definition well, so simply reformatting would do, then the next two paragraphs could be replaced by a summary of the article. Gnixon 13:55, 28 March 2007 (UTC)

The first two paragraphs only apply to our own Solar System. They don't cover the 200-odd extrasolar planets. Since this article is about "planet" rather than just planets in our Solar System, the intro should cover both. Serendipodous 14:00, 28 March 2007 (UTC)

Okay, but briefly! The definition really only needs to be a sentence or two. The article is about much more than IAU definitions. I don't have time now, but I'll take a shot at revising things later today if nobody else gets a chance to do so first. Gnixon 14:17, 28 March 2007 (UTC)

I'd be interested to see what you come up with. If you can condense those two lists into two sentences, I will be immensely impressed. Serendipodous 16:11, 28 March 2007 (UTC)

I agree. It fails the Wikipedia:Lead section definition as a stand-alone summary of the entire article. Section-wise I think the definition should take up no more than one paragraph. It would also help if the lead off were more engaging, rather than a dry discussion.

Sorry I haven't had a chance to get to this. Can someone else try? Gnixon 22:58, 2 April 2007 (UTC)

Tossing out an arbitrary example:

A planet is a large object in orbit around a star that has collapsed under its own gravity, but has too little mass to undergo nuclear fusion. When a star is first formed, it may be surrounded by a protoplanetary disk of matter. Through a process of accretion, larger bodies form in this disk and these sweep up or eject most of the remaining matter. What remains is a system of planets in orbit around the star, plus some amount of debris that can form minor-planets.

The decay of radioactive material in the core of a planet, as well as the energy generated by the gravitational collapse, can provide an internal heat source. This thermal energy can melt part of the interior, allowing mass segregation to occur, and potentially driving tectonic activity and forming a magnetic field. A planet can also accumulate an exterior atmosphere, which can be massive in the case of a gas giant planet such as Jupiter.

Historically, ...

— RJH (talk) 22:45, 2 April 2007 (UTC)

If that must be used, I would rather it said, "an object in orbit around a star that is large enough for its own gravity to have rounded its shape..." rather than "collapsed under its own gravity"- collapsing under their own gravity is what stars do. Serendipodous 12:27, 3 April 2007 (UTC)

I think that's the right idea, but I recommend using the IAU's words exactly if they're not too verbose. I might open like "Planets in our solar system have recently been defined by the IAU as.... Historically, planet was defined more loosely, so that ...9 planets... however, under the new definitions ...." Then I'd continue with an overview of all the other parts of the article. Gnixon 13:59, 12 April 2007 (UTC)

The problem with wikipedia is that you can spend a long time on an article editing in a group with a group of editors, accomodating everyone's concerns. Then someone comes along and says its misleading/inaccurate and requires a new write-up in a more technical way. Then when its finally been sorted someone else comes along and says its too technical and long-winded! Originally we had a more vague definition that kept close to the IAU's terms but covered both solar and extrasolar definitions in one sentence. Perhaps now the redefinition furore has died down we might be able to bring that one back? The Enlightened 15:40, 13 April 2007 (UTC)

I think it's a very good idea to define planet precisely using the IAU's words, since their definition is highly notable these days. However, we also have to remember that this whole article isn't about IAU definitions, so the lead shouldn't be, either. We need a good writer to condense those definitions into readable prose within 1 or 2 paragraphs, then write another couple paragraphs for the intro about the rest of the topics covered in the article. Gnixon 15:45, 13 April 2007 (UTC)

I've had a go at consensing the first paragraph, though I'm less certain about what to do with the third. Serendipodous 16:16, 13 April 2007 (UTC)

Good start. I tried to start revising the lead, but didn't get too far. This is tough. I'm thinking it might be best to start by introducing the recent controversy. Something like, "After much debate following the discovery of (mention Eris vs. Pluto)..., the Inter. Ast. Union has defined a planet to be .... In a separate resolution...." (new paragraph) Our Solar System thus has ..., along with ... (dwarf planets). Outside of our Solar System, over 200 extrasolar planets have been discovered orbiting other stars." Then we'll have devoted 2 paragraphs to defining things and we can move on to what the rest of the article talks about. Gnixon 19:54, 13 April 2007 (UTC)

The most important part of a lead section is that it is clear and brief. The dispute is covered the relevant section. I've rewritten much of the lead to make the definition clearer, added a paragraph regarding why its a notable subject, and mentioned the dispute in passing. The Enlightened 13:12, 14 April 2007 (UTC)

I like it. Gnixon 13:44, 14 April 2007 (UTC)

Yes, it's coming along. I've made two minor tweaks, placing "planet" first (rather than "The IAU") and moving the "(IAU)" to the second reference to avoid cluttering the lead sentence. --Ckatz^chat_spy 19:08, 14 April 2007 (UTC)

One thought... I like using "stellar remnant", but it needs to be defined. Obviously, this article isn't the place for it, but I couldn't find a good definition after searching Wikipedia. Anyone up to providing a concise explanation in the Stellar evolution article that we could then link to? --Ckatz^chat_spy 19:51, 14 April 2007 (UTC)

Can't take credit for the "stellar remnant" term, as I just used the phraseology found in the working definition. It doesn't have a strict definition as its just a collective term for black holes, white dwarfs and neutron stars. That stellar evolution article doesnt seem to be sensibly organised. Perhaps we should group the three of them under a "stellar remnant" heading and link to that? The Enlightened 22:02, 14 April 2007 (UTC)

Indian planets

A while back, an Indian wrote a comment on how the planets are named in India. I asked for a citation and today got this: [6]. Now I don't know the first thing about Indian astronomy, but that doesn't look like a historical description; it looks more like the ideas of one astrologer. What do you think? Serendipodous 16:20, 30 March 2007 (UTC)

I'm not sure about the validity; however, in the interim, I have updated the text with internal links (and removed the external link in the process.) --Ckatz^chat_spy 17:57, 30 March 2007 (UTC)

Re: your tweaks - better. Thanks. --Ckatz^chat_spy 18:08, 30 March 2007 (UTC)

Thanks for the thanks :). My problem with this, and it's one I've had for a long time, is that India is a multilingual and multicultural society and I'm not entirely sure that the Vedic traditions hold even for the majority of Indians. I've tried to get a straight answer out of some of the Indian contributors to this forum on this issue but it's just too complex. Serendipodous 18:10, 30 March 2007 (UTC)

HD 188753 Ab has been shown to not exist (see wiki entry)

I've removed the paragraph regarding the disproven/disputed planet HD 188753Ab. While a discussion of the claim and subsequent debunking of that planet is interesting, it hardly deserves its own paragraph (or even sentence) in the "planet" article. —The preceding unsigned comment was added by Enfolder (talk • contribs) 01:58, 9 April 2007 (UTC).

Looks like a good edit. Gnixon 03:01, 10 April 2007 (UTC)

Planetary interiors

I've added a small para on planetary interiors, but it needs a more informed description of the mechanism behind rotating magnetic fields, and why some planets have them, and some don't. Serendipodous 20:25, 28 April 2007 (UTC)

Wandering star merge

I just noticed a tag on Wandering star suggesting that it be merged with the Planets#Etymology section.--mikeu 11:39, 1 May 2007 (UTC)

Doesn't seem particularly relevant to the planet article; I don't see where the allusions could be worked in, for example. That article badly needs some citations and a little more meat on its skeleton, but no I don't think it should be merged with this one. Naked eye planet would be a far better fit. Serendipodous 11:48, 1 May 2007 (UTC)

Openening section (again)

Regarding the last two paragraphs in the opening section, I believe there is a tendency in wikipedia to sort things in a chronological fashion. I think this is a tempting, but lazy, way to organise information, especially in an article introduction. We should mainly be focusing on what the current status of things is; disagreements and controversies should be listed last. Thus we should first describe how a planet is currently defined and then follow it up with the fact that this view is contested, not list the introduction as a narrative. The Enlightened 20:31, 7 June 2007 (UTC)

NewSolarSystem2.jpg

File:NewSolarSystem2.jpg

NewSolarSystem2

Was going to explain my son why do we see light from the Sun during the day, and do not see it at night using this image! :) But it has a really important mistake. All the planets have a shadow on the side which is closer to the Sun.

If someone has a better Image of Planets, put it instead of this one, please. If no one has it, it is better to remove the image which cause unreal perception of reality :)

oleg24 14:17, 18 Jun 2007 UTC

Please add the link to the Occitan Wikipedia

oc:Planeta . Thank you very much, [[:oc:Utilizaire:Joao Xavier|João Xavier

I'm afraid we cannot do so since we would then be compelled to add links to the planet articles in all the different wikipedias, which would take up a considerable amount of space. Also, I don't really see why we would link to the oc:PLaneta page, as anyone interested in it could find it simply by doing a search in the Occitan wikipedia. Vsst 02:04, 15 July 2007 (UTC)

Added. Vsst, it is absolutely important to include links to the same article in other language wikipedias when possible. Click edit and have a look on the bottom of article; the links are what inform the link in the "in other languages" box and don't take up a "considerable amount of space." siafu 02:14, 15 July 2007 (UTC)

Ah, my apologizes. I missed that. Vsst 02:25, 15 July 2007 (UTC)

Metallicity issue

The following paper appears as though it will present some interesting insights regarding the relation between metallicity and planet formation:

L. Pasquini; et al. "Evolved stars hint to an external origin of enhanced metallicity in planet-hosting stars". Retrieved 2007-07-23. {{cite journal}}: Cite journal requires |journal= (help); Explicit use of et al. in: |author= (help)

Here's a related news release:

Luca Pasquini & Artie Hatzes (July 6, 2007). "Star Surface Polluted by Planetary Debris". ESA. Retrieved 2007-07-23.

— RJH (talk) 17:59, 23 July 2007 (UTC)

Etymology

I'm a little confused by the part that says "Today, most people in the western world know the planets by names derived from the Greek pantheon of gods." This is followed by "they are known by their Roman (or Latin) names, rather than the Greek." How does is this different from saying (more concisely) "Today, most people in the western world know the planets by names derived from the Roman pantheon of gods." Perhaps those first two sentences could be replaced with:

Today, most people in the western world know the planets by names derived from the Roman pantheon of gods, rather than by their Greek counterparts, because of the influence of the Roman Empire and, later, the Catholic Church.

Thoughts? Ben Hocking ^{(talk|contribs)} 13:54, 24 July 2007 (UTC)

The main issue is to distinguish between the Greek names for the planets, such as Phainon and Stilbon, and the Greek gods' names, such as Kronos and Ares, which are the ones we now use, though in Roman guise. Perhaps changing "Greek" to "Olympian" would be a good idea. Serendipodous 14:50, 24 July 2007 (UTC)

OK, thanks. I like your changes. Ben Hocking ^{(talk|contribs)} 14:54, 24 July 2007 (UTC)

Geocentric/Heliocentric

Regarding the recent "discussion" about whether those planets are in increasing order of their distance from the Sun or Earth, objectively they are most definitely in increasing order of their distance from the Sun. If you want to present it in a Heliocentric framework, the order of the planets should also be changed to Venus, Mars, Mercury, Jupiter, Saturn. (Actually, I'm not sure about Mars and Mercury as they're both very close in their average distance from the Earth. Using the Bode's law shortcut of 4, 7, 10, 16, 28, etc., you'll see that Earth (10) is equidistant from Mercury (4) and Mars (16).) So, either it needs to be changed back to/left as "Sun" or the order needs to be changed (and someone needs to figure out the correct order). Alternatively, it could be worded to mention that it's in order of their period of "orbit", but then you have to calculate the synodic period from the Earth. Ben Hocking ^{(talk|contribs)} 12:26, 27 July 2007 (UTC)

I've restored the text "Earth" as both the reference (#11) and the article geocentric model appear to outline that order. (While your points about the actual relative distances are valid, keep in mind that the text is referring to what they believed way back then.) Thoughts? --Ckatz^chat_spy 17:18, 27 July 2007 (UTC)

I've read the source and found what you're talking about. The order they provide (although they do it in reverse order) is: Venus, Mercury, Mars, Jupiter, Saturn. I'll update the page accordingly. Ben Hocking ^{(talk|contribs)} 17:24, 27 July 2007 (UTC)

Specifically:

For the Stella (Star) that is called Saturnus’, the Greek name for which is Phaenon (the shiner), which is the farthest away from the earth, completes its orbit in about thirty years, in the course of which is passes through a number of remarkable phases, at one time accelerating and at another time retarding its velocity, now disappearing in the evening, then reappearing in the morning, yet without varying in the least degree throughout all the ages of eternity, but always doing the same things at the same times.

Below this and nearer to the earth moves the Stella of Jupiter, called Phaethon (the blazing), which completes the same circuit of the twelve signs of the zodiac in twelve years, and makes the same variations during its course as the star of Saturnus.

The orbit next below is that of Pyroeis (the fiery), which is called the Stella of Mars, and this covers the same orbit as the two planets above it in twenty-four months all but (I think) six days.

Below this in turn is the Stella of Mercurius, called by the Greeks Stilbon (the gleaming), which completes the circuit of the zodiac in about the period of a year, and is never distant from the sun more than the space of a single sign, though it sometimes precedes the sun and sometimes follows it.

Lowest of the five Stellae and nearest to the earth is the star of Venus, called in Greek Phosphoros (the light-bringer) and in Latin Lucifer when it precedes the sun, but when it follows it Hesperos; this planet completes its orbit in a year, traversing the zodiac with a zigzag movement as do the Stellae above it, and never distant more than the space of two signs from the sun, though sometimes in front of it and sometimes behind it.

Ben Hocking ^{(talk|contribs)} 17:29, 27 July 2007 (UTC)

Interesting - I missed that part, and left the order intact based on this drawing: Image:Ptolemaicsystem-small.png (It conflicts with the text information as it has Mercury closest to Earth.) Thoughts? --Ckatz^chat_spy 17:50, 27 July 2007 (UTC)

There was no set order to the cis-Solar planets (the inferior planets, as they were called) in Graeco-Roman cosmology. Some put Mercury first, some put Venus first. If I remember rightly, Ptolemy put Mercury first. Since both conceptions were wrong, it ultimately didn't matter much. Serendipodous 18:00, 27 July 2007 (UTC)

(edit conflict)I saw that - Plato (4th century BC) used Venus-Mercury-etc. while Ptolemy (2nd century AD) changed it to Mercury-Venus-etc. I've restored that version, since the text explicitly mentions Ptolemy. --Ckatz^chat_spy 18:04, 27 July 2007 (UTC)

Look again at that Ptolemaic figure. Those are in order based on their distance from the Sun. (The object with flames licking out of it that surrounds the Earth.) That makes sense if you consider the epicycle model. The Sun orbits the Earth with the other objects orbiting the Sun (sort of). Well, maybe not, I don't really know, as that puts the Moon going around the Sun, too. Still, I don't know that you can draw the conclusion you're drawing from that figure. I think Ptolemy was smarter than that. If you insist on keeping that order and them going around Earth, please consider adding something like "(according to Ptolemy)" so that naïve readers don't think this is the actual order of planets in their distance from Earth. If there are any experts in ancient astronomy, I'd sure appreciate hearing from them about what Ptolemy did and did not believe! Ben Hocking ^{(talk|contribs)} 18:35, 27 July 2007 (UTC)

Hmph. After a little more research, I take it back. Maybe Ptolemy wasn't so smart. :P Still, I'd like to request the phrase "(according to Ptolemy" to make it clear that this is not the proper order of planets in their distance from the Earth. Ben Hocking ^{(talk|contribs)} 18:42, 27 July 2007 (UTC)

OK, but there was no "proper" order of the planets in the geocentric model. Since the universe is not geocentric, it doesn't really matter which order one used, it would still be wrong. If there ever was such a thing as the "official" description of the geocentric universe, it would be Ptolemy, since he superceded and supplanted all earlier thinkers on the subject. Most of the material we have about cosmologists earlier than Ptolemy comes from Ptolemy, since after Ptolemy no one saw fit to refer to them again. Serendipodous 19:32, 27 July 2007 (UTC)

Mathematically, a geocentric model of the solar system (or universe) can be constructed just as rigorously as a heliocentric model. It's just more complicated, doesn't explain the "how", and therefore fails Occam's Razor. My point is that as the sentence reads - "in increasing order from Earth" - there is a correct order. Venus is most definitely closer (on average, and for an overwhelming fraction of the time) to the Earth than Mercury. That said, Ptolemy evidently wasn't aware of this (although it appears that astronomers of prior generations were). In case you haven't figured it out already, it's hard for me to drop an argument - I hope you're not at all annoyed by that. :) Ben Hocking ^{(talk|contribs)} 19:44, 27 July 2007 (UTC)

No one was aware of that. While it is possible to discern with the naked eye when Venus and Mercury are in conjunction, because Venus is so bright, it is impossible to tell which is in front of which. Indeed, I'm not entirely sure it's possible to tell where any planet is in relation to the others (though the Sun and the Moon are fairly easy). I think the superior planets were simply ordered according to their orbital periods. The fact that this was the correct order was, if I remember correctly, coincidental. Serendipodous 19:54, 27 July 2007 (UTC)

If you order based on synodic period alone (the geocentric way), you would get the order Mercury (115.8 d), Saturn (378.1 d), Jupiter (398.9 d), Venus (583.9 d), and, finally Mars (780.0 d). Note that the superior planets are in exactly reverse order that way. If you separate inferior from superior (by putting inferior first) and order them in the reverse synodic period order (which would be appropriate, if you understand the synodic calculation, which they arguably might not have), you get Venus, Mercury, Mars, Jupiter, and Saturn. :D Ben Hocking ^{(talk|contribs)} 22:03, 27 July 2007 (UTC)

It's times like this that I wish the Almagest was available in online translation. In truth I don't know why it isn't; it's been translated into English for at least a century, surely some editions are in the public domain by now. Serendipodous 06:43, 28 July 2007 (UTC)

Yeah, no such luck. I tried Project Gutenberg, and then just Google. What I did find was this:

Stevenson, Edward Luther. Trans. and ed. 1932. Claudius Ptolemy: The Geography. New York Public Library. Reprint: Dover, 1991. (This is the only complete English translation of Ptolemy's most famous work. Unfortunately, it is marred by numerous mistakes and the placenames are given in Latinised forms, rather than in the original Greek).

So, less than a century, identified as the only complete English translation, very possibly still under copyright, and of inferior quality. :PBen Hocking ^{(talk|contribs)} 16:09, 28 July 2007 (UTC)

OK, while this is getting attention

I've been trying to work this section into a form that is comprehensible (it does tend to bombard the reader with unfamiliar information) and have found that the simplest compromise, to avoid the confusion mentioned above, is to employ the term "Olympian" to describe the pantheon of the Greeks and the Romans together, thus allowing me to circumvent the term "Graeco-Roman", since that would require me to bring the Romans into the article earlier. The problem, as one editor pointed out in invisotext, is that Saturn (Kronos) was not an Olympian, but a Titan. I've attempted to make the distinction clear in the text, but I doubt anyone unfamiliar with the topic will notice it. Is this bit of misinformation an acceptible fudge, or is a more fundamental rewrite in order? Serendipodous 18:00, 27 July 2007 (UTC)

As the author of the "invisotext", I'd like to say that I think it's an acceptable fudge. Ben Hocking ^{(talk|contribs)} 18:43, 27 July 2007 (UTC)

Why does list of planets redirect here?

I fail to notice any list. TheBlazikenMaster 20:25, 29 July 2007 (UTC)

Well, there are only 8 planets in the solar system, and there's a list of them at Planet#Within the Solar System. A more comprehensive list that included extrasolar planets would be an interesting idea, but it would mostly consist of catalogue numbers. Serendipodous 20:32, 29 July 2007 (UTC)

I think there is enough information available now to provide a table of estimated mass and orbital distance for many of the planets, as well as their host stars, distance from the Sun and date of discovery. (Possibly grouped by the star name?) Use of the table sorting functionality would also be beneficial. So a separate article would be worthwhile, especially given the rate of new planet discoveries.

Although now that I look at it, the List of stars with confirmed extrasolar planets article has that covered pretty well. There might be a need for a page called Lists of planets then. — RJH (talk) 22:36, 14 August 2007 (UTC)

GA-worthy?

I think this article is GA-worthy now. Is anybody going to go for it? — RJH (talk) 22:25, 14 August 2007 (UTC)

Needs a few more citations. Also I think the "In the Solar System" section has a few too many subsections. Perhaps the "Attributes" section could be reworded to suggest that, as these attributes apply to our Solar System's planets, they could also apply to other systems. There is already some information about weather systems on extrasolar planets, and we do know their orbital elements pretty well. Serendi^podous 13:36, 15 August 2007 (UTC)

Issue that has resulted from this: do we know if all extrasolar planets, like the planets in our solar system, orbit in line with their star's rotation? Serendi^podous 12:34, 17 August 2007 (UTC)

I'd have to say no, for the reason that astronomers don't always know a star's axis of rotation, nor the planet's orbital plane. But wouldn't it seem a reasonable conjecture to say that in many cases they are closely aligned since they formed from the same rotating disk of material? — RJH (talk) 16:46, 19 August 2007 (UTC)

That is an assumption based on the hypothesis that all planets orbit in prograde directions. If we don't know that, we can't make that statement. That's why I asked. Serendi^podous 08:13, 21 August 2007 (UTC)

The following sentences in the lead section struck me as a bit out of place:

Thus planetary science is essential not only to comprehend the structure of the universe, but also to better understand the development of life, and to aid the search for extraterrestrial intelligence. Additionally, the planets visible from Earth have played a vital role in the shaping of human culture, religion and philosophy in numerous civilisations. Even today, many people continue to believe the movement of the planets affects their lives, although such a causation is rejected by the scientific community.

The lead is supposed to be an overview of the article, but nowhere else do I see life or extraterrestrial intelligence discussed in more detail. Nor is there a discussion of cultural, religious or philosophical effects, or a coverage of astrology. Shouldn't this either be covered in the article or else removed? Thanks. — RJH (talk) 16:43, 19 August 2007 (UTC)

Peers said the lead should be expanded, and that's what an editor came up with to do it. Serendi^podous 09:56, 20 August 2007 (UTC)

Is there any objection to the removal of that input? Or is the preference to expand the article so as to cover those topics? — RJH (talk) 19:05, 20 August 2007 (UTC)

The only objection I would have is what to replace it with. Serendi^podous 19:11, 20 August 2007 (UTC)

Well frankly the lead is not a summary of the article, and that would provide an an objection during a FAC. So my suggestion would be to re-write it. — RJH (talk) 20:59, 22 August 2007 (UTC)

Well, it summarises the article now, but is it long enough? Serendi^podous 21:15, 22 August 2007 (UTC)

It still seems a little weak on the coverage of the Attributes section. In particular it should at least mention that most planets have elliptical orbits, axial tilt and rotation. The length seems fine, however. WP:LEAD recommends 3-4 paragraphs for articles over 30,000 characters. — RJH (talk) 17:09, 4 September 2007 (UTC)

OK, I've expanded the lead a bit. Do you think that the Atributes section should be cited? Serendi^podous 18:31, 4 September 2007 (UTC)

I've arrived at this discussion late, and I entirely oppose the changes that have been made. The lead section before was agreed upon by many editors and widely accepted. This is also notable, from the lead section page: '"Get the lead right first. Construct an introduction for the article as if it were a good encyclopedia page, even if it has not yet arrived at that point. The lead is the first thing the readers sees and, sometimes, all that they read."' The lead section should summarise the main points, not be a summary of the article, section by section, which will just cause it to be badly written. The Enlightened 09:15, 15 September 2007 (UTC)

It's hard to argue though that the old lead didn't introduce facts and statements the article doesn't cover. Serendi^podous 10:05, 15 September 2007 (UTC)

Then that's a problem with the article as it stands, and those bits need to be added to the article. The WP for lead section quite clearly states the intro should explain why the topic is important. The fact that planets are widely considered the most feasible environment for life is probably the most important fact on the whole subject - certainly far more notable than the tilt of orbits! The astrology mention is also important, with the tie-in to the more appropriate articles, and we should also have a section discussing the culture of the planets in Europe, India, China and other regions of the world. —Preceding unsigned comment added by The Enlightened (talk • contribs) 15:44, 15 September 2007 (UTC)

Personally I don't really understand why the topic of ET life has to be tied specifically to planets, especially since the most likely target for extraterrestrial life in our Solar System is a moon. For all we know, ET life could form on the surface of stars, or in interstellar space. The topic of ET life really is too broad to form a subset of "Planet." I agree on astrology though. Some mention of it should be made somewhere. Serendi^podous 16:07, 15 September 2007 (UTC)

Are Planetary Systems Filled to Capacity?

There's a very intriguing two-part essay in the Astrobiology Magazine on the subject of planet formation:

Soter, S. (2007) Are Planetary Systems Filled to Capacity?

• part 1
• part 2

— RJH (talk) 19:08, 20 August 2007 (UTC)

I think that article would be better placed at nebular hypothesis, Formation and evolution of the Solar System, Cleared the neighbourhood or extrasolar planet. Serendi^podous —The preceding signed but undated comment was added at 21:41, August 21, 2007 (UTC).

No doubt. It's interesting reading though. — RJH (talk) 21:02, 22 August 2007 (UTC)

Good article nomination on hold

This article's Good Article promotion has been put on hold. During review, some issues were discovered that can be resolved without a major re-write. This is how the article, as of October 4, 2007, compares against the six good article criteria:

1. Well written?: I would consider refocusing the lead: Yes, a brief mention of how planets were considered and the 2006 IAU decision are warrented, but I think the emphasis on history is a little heavy. Rest of the article is fine, with the only questionable part would be the need for the "Former Planets" section, since you basically have identified these already in the prose.

2. Factually accurate?: No apparent problems

3. Broad in coverage?: Good coverage, no apparent problems

4. Neutral point of view?: Seems fine to me

5. Article stability? Ignoring recent vandalism, looks fine

6. Images?: Check these; a few seem to lack any copyright notice (definitely the first picture on the page is missing info).

Please address these matters soon and then leave a note here showing how they have been resolved. After 48 hours the article should be reviewed again. If these issues are not addressed within 7 days, the article may be failed without further notice. Thank you for your work so far. — MASEM 04:03, 4 October 2007 (UTC)

The lead image is an alternate version of this NASA image. I've added a link to the original image and noted that it was NASA-created. All the other images are public domain. Serendi^podous 08:45, 4 October 2007 (UTC)

You still need to include licensing (even if it remains PD after the modification) on the image, and a summary for the modification. Nothing too difficult, just to prevent the image from being misunderstood as a possible non-free work. --MASEM 12:39, 4 October 2007 (UTC)

OK How's that? Serendi^podous 14:04, 4 October 2007 (UTC)

Works for me. I'm still up in the air about the lead and "Former Planets" section, trying to think how that could be improved otherwise --MASEM 23:50, 4 October 2007 (UTC)

GA Passed

GA review (see here for criteria)

1. It is reasonably well written.

   a (prose): b (MoS):

2. It is factually accurate and verifiable.

   a (references): b (citations to reliable sources): c (OR):

3. It is broad in its coverage.

   a (major aspects): b (focused):

4. It follows the neutral point of view policy.

   Fair representation without bias:

5. It is stable.

   No edit wars etc.:

6. It is illustrated by images, where possible and appropriate.

   a (images are tagged and non-free images have fair use rationales): b (appropriate use with suitable captions):

7. Overall:

   Pass/Fail:

On the 1b, I still think there might be something better as the WP:LEAD, not that what's there is bad or unpassable, but the rest of the article seems fine. Good job! --MASEM 23:59, 12 October 2007 (UTC)

What I would like for this article

is a credible source that states the first recorded observation of a moving planet. I believe this to be the Babylonian Venus tables, but I have not been able to establish that. If I can get ahold of a source that shows that the Babylonians were the first people to recognize the motions of the planets (other than the Sun and Moon, of course) then I can tie it to astrology, which would link the rest of the article more firmly to the lead. Serendi^podous 07:33, 13 October 2007 (UTC)

They may be the first recorded people, but it's highly doubtful they were the first. The movement of the planets is just too obvious to be ignored by anyone who watches the sky. kwami 10:27, 1 November 2007 (UTC)

Well obviously. But since history is reliant on records, the first recorded mention will have to do. Serendi^podous 21:28, 1 November 2007 (UTC)

Ceres: Terrestrial or Ice Dwarf?

The rational of the Dawn probe is to visit one "dry" (rocky) asteroid, Vesta, and one "wet" (icy) one, Ceres. Wouldn't this make Ceres an ice dwarf? kwami 10:27, 1 November 2007 (UTC)

Bad phrasing. Pluto is MADE of ice. Ceres is a rock with ice on it. I'll rework it.

Oh. I thought you were referring to to a line in the article. No, Ceres isn't an ice dwarf; it just has more ice than Vesta does, which has none at all.Serendi^podous 10:33, 1 November 2007 (UTC)

Actually, I was talking about the article. I was thinking of Jupiter's "icy moons", which seem like they may have a composition not unlike Ceres. By saying Ceres is a terrestrial body, the implication for me is that it's dry like Earth. kwami 18:08, 1 November 2007 (UTC)

Again, the moons of Jupiter are MADE of ice. Ice on the moons of Jupiter behaves the way rock does on Earth. Ceres is a rocy body with some ice on top of it. It is no wetter than Earth, really. Serendi^podous 18:10, 1 November 2007 (UTC)

Excepting Io... 132.205.99.122 (talk) 23:17, 22 November 2007 (UTC)

From the articles here, it would appear that Ceres has an ice mantle about the relative thickness of Ganymede's, and greater than Europa's. At the upper estimate, a 120km ice mantle on a 475km body, Ceres would be 60% ice, compared to Ganymede's 50% and Europa's 20% (~100km on a 1560km body). Even at the lower 60km estimate, Ceres would be a third ice. kwami 19:17, 1 November 2007 (UTC)

Got rid of it. I don't think this distinction between "terrestrial dwarfs" and "ice dwarfs" is made in the scientific literature anyway; I think it's just something an editor made up. So it should go regardless. Serendi^podous 19:59, 1 November 2007 (UTC)

a simple question not answered by the article

The article doesn't say what the biggest known planet is :-( —Preceding unsigned comment added by 24.148.118.190 (talk) 08:48, 2 December 2007 (UTC)

Info added. Though the question is not as simple as it seems. :-) Serendi^podous 09:37, 2 December 2007 (UTC)

Five or Seven Ancient Planets?

The historical part of this article discusses the five planets, suggesting that the inclusion of the Sun and Moon was something of an anomaly. As I understand the sources, in ancient uses the term planet normally meant the seven planets, including the Sun and the Moon, but occasionally ancient writers such as Ptolemy speak of the Five planets (Penta planetoi). This restrictive term was used to exclude the Sun and Moon which were normally included in the unrestricted term, planet.

Does anyone object to a rewrite to incorporate this historical understanding into what is principally a scientific article? --SteveMcCluskey (talk) 21:55, 6 January 2008 (UTC)

See Definition of planet Serendi^podous 22:44, 6 January 2008 (UTC)

No, it should be in there. After all, that's why we have a seven-day week. kwami (talk) 00:51, 7 January 2008 (UTC)

Serendipodous: Thanks for pointing that out. There is a nice discussion of the historical understanding of the term in Definition of Planet. But now I'm wondering why there should be such inconsistency between the two articles on this point. Like Kwami, I think it is a meaningful point and should be included.

Anyway, I'm off to the AAS convention tomorrow and will get back to this when I return. --SteveMcCluskey (talk) 01:26, 7 January 2008 (UTC)

Clearing the neighbourhood

This section needs a clear and concise statement of why Neptune is considered to have "cleared its neighbourhood", in spite of the presence of Pluto - the absence undermines the whole new-definition arguement. 82.10.108.49 (talk) 13:04, 2 February 2008 (UTC)

Look at the table in Cleared the neighbourhood. Neptune has a Stern-Levinson parameter of 2.7×10⁵, and a planetary descriminant of 2.5×10⁴. The former measures the theoretical capability of the planet to clear its neighbourhood (the least effective planet is Mars at 915; the most effective dwarf planet is Eris at 0.005); the latter measures the actual extent at which the neighbourhood has been cleared (the least effective planet is Neptune at 2.4×10⁴; the most effective dwarf planet is Ceres at 0.33). There is a huge gulf in the values between the planets and the dwarf planets. I'm not sure whether Pluto counts as being in the neighbourhood of Neptune, but if it does, then consider both that Neptune is enormously massive than Pluto, and also the fact that Pluto is locked in an orbital resonance with Neptune. No planet is able to 100% clear its neighbourhood - there will always be stable positions locked in orbital resonance with the planet (e.g. the Trojan asteroids in Jupiter's orbit. Bluap (talk) 15:31, 2 February 2008 (UTC)

Neptune DOMINATES Pluto. Pluto gets closer to Uranus (11AU) than it does Neptune (17AU). [7] Back in the 1960's Pluto was only 15AU from Uranus. -- Kheider (talk) 08:21, 3 February 2008 (UTC)

Error

According to the cited IAU resolution passed in Prague, a planet must orbit the Sun - it is not extended to objects orbiting other stars. This restriction is possibly due to the difficulty in determining whether an object orbiting another star has satisfied the "clearing its orbit" criterion. Secondly, the IAU does not say that the orbit clearing criterion is limited to "planetessimals" nor does it say "region". Specifically, resolution 5A states that a planet "has cleared the neighbourhood around its orbit". Bassesq (talk) 07:35, 3 February 2008 (UTC)

The definition up top combines two separate IAU declarations, one made in 2006, which deals with planets in our Solar System, and one made in 2003, which deals with extrasolar planets. The two compliment each other and don't really interfere, so they can be combined without too much trouble. Serendi^podous 10:18, 3 February 2008 (UTC)