Talk:Planet/Archive 4

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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

---
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. --Ckatzchatspy 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? --Ckatzchatspy 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: [1]. 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.) --Ckatzchatspy 17:57, 30 March 2007 (UTC)
Re: your tweaks - better. Thanks. --Ckatzchatspy 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

Image: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". 

Here's a related news release:

Luca Pasquini & Artie Hatzes. "Star Surface Polluted by Planetary Debris", ESA, July 6, 2007. Retrieved on 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? --Ckatzchatspy 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? --Ckatzchatspy 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. --Ckatzchatspy 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. Serendipodous 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? Serendipodous 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. Serendipodous 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. Serendipodous 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. Serendipodous 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? Serendipodous 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? Serendipodous 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. Serendipodous 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. Serendipodous 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?

— 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. Serendipodous —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)

GA On hold

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. Serendipodous 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? Serendipodous 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. Serendipodous 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. Serendipodous 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.Serendipodous 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. Serendipodous 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. Serendipodous 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. :-) Serendipodous 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 Serendipodous 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). [2] 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. Serendipodous 10:18, 3 February 2008 (UTC)