Talk:Iapetus (moon)

Capitalisation?

I see throughout the article, "lapetus" is written with a lowecase "l". Is this intentional? I would have thought that, being a proper noun, it should always be written Lapetus? --GrahamDo (talk) 08:14, 28 February 2008 (UTC)

It's not lapetus, it's Iapetus. It helps if you have a font that distinguishes el from i! kwami (talk) 08:50, 28 February 2008 (UTC)

This is the exact reason why I wish the spelling "Japetus" had won out... Double sharp (talk) 14:16, 17 October 2021 (UTC)

Pronounciation

Usonian pronunciation eye-ap'-a-tus, British jap'-a-tus. Adjectival form Iapetian, Japetian, stress on the e: eye'-a-pee'-shun, ja-pee'-tee-un.

Copy

I notice that this article bears a clear relationship to this website: http://www.solarviews.com/eng/iapetus.htm

Not sure if permission was given, or what the situation is. If not, then the page needs to be rewritten. If so, the permission or explanation should be given here on the talk page.

--Chinasaur 06:25, 30 Jun 2004 (UTC)

I've just given the text a thorough reworking, but since I used only the questionable text itself as a source I'm still a little wary of the similarity. I'll go hunt for some new material to add in and hopefully diverge this article even farther. Bryan 07:39, 30 Jun 2004 (UTC)

There. What do you think? Bryan 08:02, 30 Jun 2004 (UTC)

2001

-- I just read ACC's 2001, and as I recall, it described a white ellipse, like an eye, centered on the moon's equator and aligned towards the poles, with the monolith exactly in the centre. I don't remember anything about this "white circle in a black circle" business. It can't come from the movie either, because Discovery only went to Jupiter in the movie. Thoughts?? ryan 13:57, 18 Aug 2004 (UTC)

You could be right, I based that comment on foggy memories of 2001 and some later comments by Clarke. The essence of what I wrote is true, but I may have misremembered the details. If anyone has a copy of 2001 to hand, please correct my work! The Singing Badger 14:43, 18 Aug 2004 (UTC)

--

It's actually on the surface of Iapetus in the book, in the center of the white region, like the pupil of an eye. Bowman actually goes down to the surface with one of Discovery's pods, reasoning (correctly) that the surface gravity of the moon is low enough that he could return to the ship orbiting the moon using the weak navigational thrusters on the pod. Of course, he never does come back... Cakedamber

Just read your remarks and checked the book. I don't know how I could have missed it -- guess the sequence from the movie influenced my perception. There is no actual line in the book saying that the second monolith "stood on the surface." However, in chapter 38, while making his request to go EVA, Bowman says: "If it appears safe, I'll land beside it -- or even on top of it." He could land beside it only if ot was on the moon's surface. So you're right on this one.

But in 2010: Odyssey Two, the monolith is not on Iapetus surface, but up in space. In the movie 2001, if I'm not mistaken, there's a scene where you see the monolith fly around in space, too. --213.80.3.66 09:49, 22 February 2006 (UTC)

In the movies and subsequent books the monolith orbits Jupiter. Only in the book 2001: A Space Odyssey Iapetus is the location of the monolith.--Jyril 12:27, 22 February 2006 (UTC)

BTW -- Why isn't this discussion in the 2001: A Space Odyssey (novel) page?

Robeykr 03:09, 6 Jun 2005 (UTC) (Talk)

It's in reply to a trivia fact about Iapetus. --Patteroast 10:14, 9 Jun 2005 (UTC)

Also, should something be included about Iapetus being featured in 2001? Worldthoughts 01:39, 9 July 2007 (UTC)

Another wrongly placed discussion

abbreviations: DP = dwarf planet; HE = hydrostatic equilibrium

When you say about Haumea it looks nearly round it means imho something quite different from the actual shape of Haumea... Too bad... I'll die idiot... Never knowing how Haumea became a planet while Haumea was not on those dwarf planets initial list... ONaNcle (talk) 07:38, 10 September 2013 (UTC)

The definition is HE. "Nearly round" is an attempt to avoid jargon. The only problem is that Iapetus, at 1,470 km, turns out not to be in HE after all, though it's quite nicely ellipsoidal, so we can't be sure Haumea and Makemake are really DPs. It's not a practicable definition. — kwami (talk) 10:39, 10 September 2013 (UTC)

I don't see what Haumea has to do with this article; but is it known that Iapetus is not in HE?? The article doesn't say so, in fact it mentions a "hypothesis" that "states that the bulge is in isostatic equilibrium typical for terrestrial mountains". Objects bigger than ~800km should all be in HE, theoretically, and Iapetus looks "round" enough to me. --Roentgenium111 (talk) 13:29, 10 September 2013 (UTC)

I've seen an article somewhere that claims that Iapetus (and, for that matter, several other, but not all of the, round moons of Saturn) is not in HE, because its axes are inconsistent with a body in HE with its rotation period. It would mean that bodies of similar size, and, for that matter, Pluto(!) and Eris, could technically not be in HE. My guess is that these bodies' shapes achieved HE somewhere in the past when they rotated more rapidly, after which their shapes froze in; and that the shapes of the moons such as Rhea (which is claimed to be in HE) just froze in relatively later when they already rotated more slowly. The lack of technical current HE would make them similar to Phoebe and Vesta, both of which achieved HE somewhere in the past. --JorisvS (talk) 13:45, 10 September 2013 (UTC)

Sorry to disturb but even if I guess DP stands for dwarf planet, I've no idea about HE; certainly not helium. Jacques Ovion aka 82.224.88.52 (talk) 14:54, 10 September 2013 (UTC)

Hydrostatic equilibrium. I have also added what the abbreviations stand for at the top of this subsection. --JorisvS (talk) 15:00, 10 September 2013 (UTC)

(2xEC) I see, so the problem is the general form, not the ridge? Searching, I've found this as a possible reference for the claim. On the other hand, Brown claims that "Anything [icy] larger than 600 km is all but certainly round" and "All icy satellite larger than 400 km are round" (using "round" as synonym for "in HE", apparently), contradicting the claim. So who's right? (And do you remember what's the largest moon claimed not to be in HE, if not Iapetus?) --Roentgenium111 (talk) 15:03, 10 September 2013 (UTC)

Your Walsh reference is (I think) referring to the paper that found Iapetus out of HE. It's not about the ridge, but about the oblateness. IIRC, the authors combined all of the images of various Saturn satellites to get a more accurate 3D model of their shapes. The result was that some moons are HE within the accuracy of the model (Rhea was good), but Iapetus was overly oblate by a few km (single digit, I forget exactly how much). However, another paper rebutts it ("Isostasy on Iapetus: the myth of fossil bulge" referenced in this article). I think the main takeaway re DPness is that we can't be certain of any candidate until we've had a good, long, close-up look. None of the DPs have observations anywhere near as good as Iapetus. Ceres will soon be determineable. Will New Horizons be able to get as good imaging of Pluto as Cassini of Iapetus?

Brown's comments are just back-of-the-envelope, and Proteus shows that the 400 km line is wrong in practice. Either it's plain wrong, and an icy body can be >400 km and non-round, or it just highlights that we can't always tell how icy a body really is. (BTW, why does Wikipedia use Brown's comments, rather than the peer-reviewed papers by Lineweaver and Cole?) Tbayboy (talk) 17:30, 10 September 2013 (UTC)

Yes, that would be a ref for Iapetus, although it is not what I've seen before.

Iapetus, like the others, is obviously round, just look at images of it. The problem is that the definition is rather strict by requiring current hydrostatic equilibrium. "Round" could be said to include not just current, but also past HE. AFAIK Brown does not specify whether he does so (I suspect not, and from his description of how he gets his estimates, he may not be very rigorous; he uses Ceres to say that rocky objects become round around ~900km, but Ceres is in fact a mixture of ice and rock, whereas rocky Vesta at less than 600 km used to be round). I'd say that given those and similar sources, Brown's just wrong. Furthermore, the DP definition using HE is just not practicable: the enormous difficulty of ascertaining whether a body's shape is consistent with current HE aside, would Rhea (which is said to be in HE) reacquire HE shape if it were to be disrupted, given that we know that a body like Iapetus is not in current HE? I suspect not, and that would make it basically impossible to tell whether a body is currently truly in HE. --JorisvS (talk) 17:40, 10 September 2013 (UTC)

One century after Albert Einstein, Brown is revealing himself as the new science pope/guru. Far below on the same talk page, one can read many wikipedians following him. My own concern is not about more or less round objects but about far away dots resolving themselves to look like circles or not. If Brown was born in an earlier century, I bet many of his followers could have tell us Saturn ring to be a planet ;-))) ONaNcle (talk) 13:19, 13 September 2013 (UTC)

Speculation that Iapetus is artificial

I really dont like this phrase: The scientific mainstream considers such ideas fanciful at best. It's so NPOV and it tries to rediculize all the section in a superior point of view, as if mainstrem science is always correct, as we all know it isnt. That section has very out of normal ideas, but we should accept it, while just saying it is not maintstream science, or something else, very mild, so that the reader can understand that is possibly incorrect and it is not supported by most scientists. These ideas are good for astronomy, cause it will make scientists look for true reasons and the public like these things. I'm not supporting an article like the one of Atlantis, but some of these exotic therories are also fascinating because it makes you wonder... -Pedro 18:05, 16 November 2005 (UTC)

I disagree; the scientific mainstream DOES consider those speculations fanciful at best. Rather, I'd say, the scientific mainstream would use words such as "nonsense" or "bullshit". I think that such fringe science theories should be presented - they are out there afterall, and they make a good read really - there is nothing wrong with pointing out that they are, well, fringy. At least the statement chosen in the article isn't insulting or anything. -- Nils Jeppe 19:57, 12 December 2005 (UTC)

I don't think such "theories" (they are, in fact, wishful thinking. There is no real evidence of Iapetus being in fact of artificial origin) deserve being mentioned at all. It is not the fact that these theories sound "wild" or "fringy" or whatever that bothers me, it's the complete lack of credible evidence to support them. If you're making an encyclopedia, try to stick to facts rather than list products of wishful thinking of a few. Making a "good read" isn't a very good reason to include such things either. - Speth, February 13, 2006

I disagree. Such "theories" should be included. The hypothesis you mention isn't just limited to a couple of cranks, you know. It just shouldn't be touted as a "fact". 70.101.145.211 02:00, 14 September 2006 (UTC)

Does everyone get a soap box now? I have a theory my dad created it. Can I post that up there? This is dedicated to information, lets try to keep the sources open, but credible.

When I hear such talk from the Mainstream Scientific "Religious" organizations, I ask... What are you afraid of? The only way to dispell [b]ANY[/b] theory is to go there with a manned crew and land and look about. This might be done with rovers but then there is still the possiability for interpertation(SP). A Manned Crew would not be able to make any judgement views, it would all be black and white. Magnum Serpentine 5 July 2006.

• In the past people believed there were seas in the Moon and Mars, so for you that should be excluded from those articles?!--Pedro 11:19, 6 July 2006 (UTC)

Such claims are completely unencyclopedic unless they have gained considerable publicity (cf. the Face on Mars). Removed.--JyriL ^talk 18:33, 3 September 2006 (UTC)

I actualy consider the evidence for this theory stronger then the Face On Mars one. —Preceding unsigned comment added by 69.131.23.208 (talk) 05:19, 16 February 2009 (UTC)

This discussion has been dead for a year. Can we remove the mergeform from the article now? Anybody against it?CWitte 12:15, 18 August 2007 (UTC)

I think the tag was related to the fresher discussion in a section below. In any case, I think it can be removed since a long discussion led to a decision to merge the speculation into Richard Hoagland rather than Iapetus. Deuar 20:11, 22 August 2007 (UTC)

Another theory for the origin of the equatorial ridge

The equatorial ridge may be the remnant of a ring around Iapetus. See http://www.agu.org/pubs/crossref/2006/2005GL025386.shtml --JyriL ^talk 18:33, 3 September 2006 (UTC)

Confusion about Mythology

Just a minor thing but, the last part of the section on the name origin (i.e. mythology) says this... "wherein he suggested the names of the Titans, sisters and brothers of Cronos (the Roman Saturn), be used.". Now correct me if I'm wrong here but I'm pretty sure Cronos and the Titans were Greek (not Roman as is being implied), and Saturn is Roman (so "the Roman Saturn" makes no sense). I think what it was supposed to say was "the Greek Saturn". So I'm going to go ahead and change it, if I’m wrong on this, revert it. --Hibernian 05:36, 18 December 2006 (UTC)

Japetus?

I doubt that it's ever spelled "Japetus". That's a ridiculous spelling as it looks like it should be pronounced with a "j" sound. Astroguy2 23:36, 4 June 2007 (UTC)

The spelling has been used, in fact from the earliest attestations of the usage (in the 19th century). The story of why there should be two spellings is complicated, and really out of place in this article; but I suppose it can be recounted here.

Latin originally did not distinguish i from j in spelling, using the same letter I for both; and even in printed texts as late as the Renaissance, the letters were often not distinguished. The letter however represented three different sounds, namely the vowels [ i ] and [ iː], and the glide-consonant [ j ] (equivalent to the English consonant "y"). In later printed texts, the convention grew of representing the vowels by I and i, and the consonant by J and j, these being pronounced differently by different nations.

In Greek, which had lost its [ j ] sound, the Greek letter iota (Greek: Ι and ι) always represented a vowel sound. However, when the Romans borrowed the name Ιαπετός as IAPETVS, because of the ambiguity of the letter I, it could be pronounced either [ iːapetus ] or incorrectly [ japetus ]. The latter was, in fact, the reading that would tend to be adopted, because initial I before another vowel was almost always [ j ] in Latin words.

Accordingly, there was a tradition of reading the name as "Japetus", with three syllables. This reading was, however, eventually displaced as scholars pointed out that in Greek the I was unquestionably a vowel, at which point "Iapetus" came to prevail. I'm not sure of the timing, but I believe that the transition was in progress at the time Herschel gave the moon its name. So in a way both forms are "right"; they just represent different traditions.RandomCritic 20:37, 24 June 2007 (UTC)

proposed merge with Speculation that Iapetus is artificial

It has been suggested to reinclude this Hoagland speculation that was removed a while back. I'm against, I see no reason to keep including all the wacky stuff this guy makes up. It is completely un-notable with regard to the astronomical object, and this little obscure "theory" should be happy that a whole article about it is allowed to live in the encycolpedia at all. Deuar 11:47, 6 August 2007 (UTC)

I strongly support deleting the speculation article without merging. If the speculation reappears here, it should be removed on sight. Wacky theories, like the Face of Mars, deserve inclusion because of their publicity (accompanied with proper debunking), but this one is way to obscure. Hoagland has about a zillion such "theories", none of which deserves inclusion. — JyriL ^talk 19:33, 6 August 2007 (UTC)

I also support removing any speculatory content like that from the Iapetus page. The theory is not even worth discussing IMHO. Ugo 19:43, 6 August 2007 (UTC)

Please note that deletion of Speculation that Iapetus is artificial is now being discussed at Wikipedia:Articles for deletion/Speculation that Iapetus is artificial. --Tikiwont 10:00, 7 August 2007 (UTC)

The absolute worst alternative would be to leave a POV fork speculative "Artificial Iapetus" standalone article as there is now. If the speculation is in Wikipedia at all, it should be in this article, where someone who Googles "Iapetus" and comes to Wikipedia will see well sourced and rational scientific information along with the speculation about it being a geodesic dome, a monument, or a deathstar, as in the Hoagland website. The Speculation that Iapetus is artificial article should be deleted, Please do not just turn up your scientific noses and ignore the speculative article. Edison 15:11, 7 August 2007 (UTC)

This should not be merged back. I don't see that the theory currently has much traction anywhere. 132.205.44.5 22:04, 8 August 2007 (UTC)

The discussion of at Wikipedia:Articles for deletion/Speculation that Iapetus is artificial has apaprently concluded with aa decision to merge with the Hoagland article rather than with Iapetus. In this light, I think the merge tag can be removed from this article. Deuar 20:08, 22 August 2007 (UTC)

Ridge discovery date

The article says the ridge was "discovered" on 31 December 2004. Possibly there was some sort of announcement about it on that date, but it was visible on photos a released publicly a few days earlier. This LiveJournal post from 27 December 2004, for example, commented on the early images. Perhaps the wording about a "discovery" date needs to be adjusted. -- Infrogmation 23:19, 6 August 2007 (UTC)

In that case I'd just replace the date with "late December 2004" as the discovery date as that was the timeframe. It wouldn't be ambiguous. The flyby was a rather leisurely one and as you say the ridge already became apparent in distant approach coverage several days before closest approach. Ugo 11:32, 26 August 2007 (UTC)

equatorial ridge image

The latest image Image:Iapetus mountains Larger.jpg seems to be broken for some reason (the link works fine but the thumbnail is not displayed). The bug was resistant to my amateur attempots at fixes, anyone have better ideas? Deuar 22:09, 16 September 2007 (UTC)

This seems to be a problem across Wikipedia with certain types of image (I'm not sure which types, though). They seem to be loading very slowly, rather than missing. Hopefully it will be solved soon. Rubble pile 13:21, 17 September 2007 (UTC)

Add section for Coated craters / Inky spots?

I added a section covering this some time ago but had it removed for some reason, I would like to ask what you think. It relates to the new pictures taken from Cassini. here and here They are could be many things so wild speculations have appeared as in the NASA: APOD states:

Iapetus itself has a density close to that of water ice, but the detailed reflective properties of the dark material suggest an organic composition.

It does sound really far-fetched in my opinion but the spots must have come from somewhere. Perhaps they are dust stains from Rhea thrown up by meteor impacts? Nicklas Hult (SE) 16:27, 19 September 2007 (UTC)

Why would an organic composition be far-fetched? Organic does not imply living organisms, merely carbon-based substances. There's organic stuff all across the solar system. Titan is practically swimming in organic goo! Ugo 16:34, 19 September 2007 (UTC)

Oh! I didnt know "organic" meant that in English. Then do you agree that this section should be added? Mine was deleted here stating it as "Untrue". What do you think? Nicklas Hult (SE) 16:50, 19 September 2007 (UTC)

Edit: Organic i.e. "Organiskt" in Swedish means that it really comes from something living. —Preceding unsigned comment added by Kenzeitak (talk • contribs) 16:52, 19 September 2007 (UTC)

You said "biological" and that is by far not the same as "organic". Organic chemistry for example deals with carbon based compounds. Anyway, I'd rather leave any speculation of APOD guys out of the page just now. It's been only a week since the flyby. BTW, the flyby closest approach was on 10th, not 12th Sep. --Ugo 16:55, 19 September 2007 (UTC)

Ah there we have it. Maybe ill try to add a subsection with more correction. Though I thought I had it all figured out, sometimes language breaches make things confusing and correct definitions are imperative for dictionaries. I havn't edited Wikipedia much really. Nicklas Hult (SE) 17:04, 19 September 2007 (UTC)

For the swedish speaking folks around: sv:organisk kemi will help you to understand the meaning of the term in your own language, which seems actually to be the same as in english, german, dutch and probably a lot of other languages... :-)--CWitte 08:26, 21 September 2007 (UTC)

I reworded that section based on the Sept. 10 flyby. Sorry, it was rather a rush job, but I wanted to get some of the new info up right away, since people will be looking for it. I read but now cannot locate the new press releases on the composition of the dark material; that bit needs to be updated. The bright/dark spots you were asking about should be included there, I think, as they fit in with why it seems there are no shades of grey. Also, some of the old hypotheses for the source may need to be revisited; I went over them only lightly. kwami 01:39, 10 October 2007 (UTC)

There is no longer a single feature name for the bright region

According to this page and its attached pdf maps, the bright region is now divided into two parts, Saragossa Terra and Roncevaux Terra. These terrae "are distinct from each other in that the former has a slightly reddish color and the latter does not." From the maps it looks like Roncevaux is the bright area north of the equator and Saragossa is the bright area south of it. Thus the big 500-km "Death Star disc" crater Engelier, at the bottom of our photo captioned "Roncevaux Terra," is actually in Saragossa Terra.

I'll see if I can fix this later today, this is just sort of a heads-up ... --Cam (talk) 08:23, 28 June 2009 (UTC)

This article doesn't mention the speculated artificial nature of Iapetus at all

I know the split article was merged into Richard C. Hoagland but there the subject only gets a measly sentence. "Speculation" of this kind is not "alien" to Wiki as we have articles like Cydonia which mention the claims about the Face on Mars and the pyramids in the Cydonia region on Mars. --Revolución talk 00:58, 1 September 2009 (UTC)

explanation

is it possible that the black stuff is natural, and that some event caoused it to be removed from the light side, and destruyed the ridge in the light side? --Ratstail91 (talk) 03:04, 15 September 2009 (UTC)

new info

could someone add this info http://edition.cnn.com/2009/TECH/space/10/07/space.saturn.ring/index.html?iref=mpstoryview sorry i dont have time right now GBizzle (talk) 19:18, 7 October 2009 (UTC)

Nor does it seem you have the time to notice this info has already been added in. Charvest (talk) 12:21, 8 October 2009 (UTC)

Spoken Wikipedia recording

I've recently uploaded an audio recording of the article. Please let me know if I've mispronounced anything! :-) --Mangst (talk) 22:46, 9 January 2010 (UTC)

I've updated the recording for this article. Basically nothing changed in the article, but I fixed pronunciation errors and added a "Statistics" section for reading the infobox. Please let me know if I've made any mistakes. Thanks. --Mangst (talk) 23:05, 18 October 2010 (UTC)

Incorrect pronunciation

In Latin there's no such sound as "eye" for vowels, neither in classic nor restored pronunciations. The pronunciation in the article is incorrect.

Iapetus or Japetus, both I and J are interchangeable, are pronounced exactly like they are written I-a-pe-tus. —Preceding unsigned comment added by 186.214.48.3 (talk) 17:24, 10 March 2011 (UTC)

The article gives the English pronunciation, not the Latin one. Dictionaries with the pronunciation /aɪˈæpɨtəs/ include the American Heritage Dictionary (published in the U.S.) and the Longman Pronunciation Dictionary (published in the U.K.).--Cam (talk) 00:24, 11 March 2011 (UTC)

Then a clarification should be added to the top of the article that the pronunciation is specific to English only. The article gives the wrong impression by giving a Latin spelling and then a Greek one, thus correlating it to other cultures unrelated to the US. And, BTW, I just noticed that Japetus has also a wrong pronunciation. The J and I in Latin are interchangeable and sound just the same.

A note at the top would help to clarify that these pronunciations are limited to the US.

—Preceding unsigned comment added by 186.214.48.3 (talk) 07:25, 13 March 2011 (UTC) 

They aren't limited to the US. We're an English encyclopedia, and so use English pronunciations. They are even coded for English. When we give Latin pronunciations, we mark them as Latin. — kwami (talk) 10:40, 25 May 2011 (UTC)

Ridge from rings

Upcoming article in Icarus on new computer modeling supporting the ridge-from-rings hyphothesis. — kwami (talk) 10:40, 25 May 2011 (UTC)

resource http://www.sciencenews.org/view/generic/id/332324/title/Iapetus_gets_dusted

Iapetus gets dusted; Saturn moon's yin-yang surface explained by Nadia Drake August 13th, 2011; Vol.180 #4 (p. 18) Science News. (Phoebe (moon)) 99.181.138.215 (talk) 01:50, 18 August 2011 (UTC)

Ridge genesis

http://www.planetary.org/blog/article/00003389/ 94.29.10.104 (talk) 19:33, 23 February 2012 (UTC)

What precisely is unusual about the inclination?

The article states the inclination of the orbit of Iapetus to the regular satellites is unusual with an unknown cause, however I am not entirely convinced it is as straightforward as the Orbit section makes it out to be. Surely a satellite at that distance would be expected to be on an inclined orbit anyway as the influence of the Sun makes more of a significant contribution to the orientation of the local Laplace plane: the infobox gives an inclination of 8.13° to the Laplace plane but 15.47° to the Saturnian equator, indicating the two planes are indeed misaligned. IIRC it is for a similar reason that our Moon is tilted relative to the Earth's equator. Admittedly though the deviation of 8.13° from the Laplace plane is quite large, more than that for the other regular satellites. 84.73.25.195 (talk) 23:11, 18 March 2013 (UTC)

Can't speak to the original comment, but I just updated the orbital info in the sidebar/infobox for Iapetus due to disagreements between the source and what was shown on the Wikipedia page as well as confusion as to the meaning of the inclination values referencing the ecliptic and Saturn's equator.

I think what the original writer must have meant is that Iapetus's inclination of 7.6 degrees relative to the Laplace plane is quite large and that this deviation is a subject of debate as to how Iapetus came to have its current orbital characteristics. Were Iapetus formed from Saturn's circumplanetary disk with no major perturbations other than the Sun, Saturn's equatorial bulge, and the inner moons, you would expect Iapetus's inclination relative to the Laplace plane to be close to zero. Hypotheses range from Iapetus being captured from interplanetary space, to some kind of impact with another body, to interactions between Saturn and some of the other gas giants in the early solar system skewing Iapetus's orbit from the expected characteristics. Also of note is that Iapetus's orbit has a very low eccentricity, which is peculiar if gravitational interactions forced Iapetus into its current inclination, as these perturbations also tend to excite the eccentricity of a body's orbit as well. A search engine query on the topic will yield some interesting information if you'd like to delve further into this. Sciencecompliance (talk) 20:34, 25 April 2022 (UTC)

HE = hydrostatic equilibrium

Proteus shows that (likely?) icy bodies above 400 km need not be in HE if they have an unusual thermal history (I also have to think about the Haumea collisional family here), but Phoebe shows that icy bodies around 200 km in diameter could still achieve HE at some point in their history, and therefore could still be round. --JorisvS (talk) 17:40, 10 September 2013 (UTC)

Is this Cole text peer-reviewed? It actually makes even stronger claims than Brown, putting the limit for icy bodies at 320 km (and for rocky at 600 km) Proteus is at least close to 400 km, but not to 320 km... --Roentgenium111 (talk) 19:04, 10 September 2013 (UTC)

Cole's web page is taken/adapted from his work in the 80s, but I don't remember if it was a paper or a book. Brown listed a reference to it in one of his papers, which is how I first found Cole's web page. Note that it is computing when the central pressure is enough to break the rigid body forces; to get to HE, you have to get that pressure at some distance away from the centre of the body, so the body has to be larger than that minimum. It also doesn't account for different material strength at different temperatures. In 2010, Lineweaver and Norman did a similar analysis, and got a value of 400 km for icy bodies ("The Potato Radius: a Lower Minimum Size for Dwarf Planets", in Proceedings of the 9th Australian Space Science Conference). They note, however, that temperature has a large effect. So a body that was in HE when it was young and warm may not be once it cools down, but it might still be coincidentally round. From the way it is written, I think the IAU DP definition requires current HE. Tbayboy (talk) 04:09, 11 September 2013 (UT

Yes. As I have already written here, that creates the problem that once a body cools down it may coincidentally look like it is in current HE, but would not rebound when disrupted, making (current) HE impracticable as a criterion. --JorisvS (talk) 07:35, 11 September 2013 (UTC)

I see; so which temperature do Lineweaver and Norman assume for their 400 km value? And do they give a "worst-case" value for a hypothetical object that is cold from the beginning? It should be higher than 400 km to account for Proteus... --Roentgenium111 (talk) 12:22, 11 September 2013 (UTC)

Here's their paper. Tbayboy (talk) 13:14, 11 September 2013 (UTC)

AFAICS, this paper does not actually derive the 400 km value from theoretical calculations, but derives only the ratio between the rocky and the icy HE values (and then compares it to the observed value of 600km/400km)...--Roentgenium111 (talk) 19:20, 25 June 2014 (UTC)

They create a formula for determining the potato radius, parameterised by density, compressive strength, and your choice of degree of potatoness (i.e., how round is round). They plug in the density and strength numbers for asteroids, and, for up to 10% allowable difference in radius (which I think would include Pallas as sufficiently round, and maybe even Vesta if spin were considered), get a value of R = 240 km (rocky asteroids). They're using the comparative observations with the icy moons to figure out what the radius was for icy moons back when they formed, since they formed at higher temperatures and thus lower compressive strength. They don't actually give the current potato radius for icy moons. Tbayboy (talk) 00:06, 26 June 2014 (UTC)

This statement in the intro "...and the largest body in the Solar System known not to be in hydrostatic equilibrium." is absolutely not explained anywhere in the article. This is very dissapointing. Bensmus (talk) 21:52, 13 April 2020 (UTC)

4 Vesta more or less round than Iapetus Haumea?

What about this (not so) round Solar object? ONaNcle (talk) 12:59, 11 September 2013 (UTC)

There, Vesta is viewed from a changing angle. If viewed from a constant angle, Vesta actually looks pretty round, except for its southern pole, which is a massive impact basin (Rheasilvia). --JorisvS (talk) 13:20, 11 September 2013 (UTC)

Vesta is clearly less round than Iapetus, that's a no-brainer. --JorisvS (talk) 14:37, 11 September 2013 (UTC)

But how Brown can pretend his beloved Haumea being a DP while Vesta not one? ONaNcle (talk) 16:33, 11 September 2013 (UTC)

Because "round" here includes not just spheres, but any (scalene) ellipsoid. Haumea can be well approximated, as far as it is known of course, by a scalene ellipsoid. I don't know if the axes are right for HE for a body with Haumea's rotation period. In any case, Haumea has not been seen up close, whereas Vesta has been seen up close ever since the HST images, e.g. this later one. --JorisvS (talk) 08:02, 12 September 2013 (UTC)

Think what would happen if they were to melt: Vesta would change shape. Haumea wouldn't (or so Brown believes). — kwami (talk) 18:51, 12 September 2013 (UTC)

Well, at present we probably can't really tell for sure whether Haumea would change its shape or not (though, yes, Brown seems to believe it wouldn't). Iapetus, however, would change its shape if it were to melt. --JorisvS (talk) 19:38, 12 September 2013 (UTC)

It's not just Brown who "believes" Haumea to be a dwarf planet - that's the official IAU position. I don't know any RS claiming otherwise... --Roentgenium111 (talk) 20:32, 12 September 2013 (UTC)

That was an assumption made for bureaucratic purposes (which body gets to name it), not a scientific assessment. They even said that if Haumea turns out not to be a DP, it would be reclassified but get to keep its name. Everyone assumed at the time that Haumea must be in HE; the only argument was that a lot of smaller bodies were too. Now the assumption no longer looks so secure. — kwami (talk) 22:55, 11 April 2014 (UTC)

IAU did declare Haumea to be a dwarf planet back then, that was independent of the "bureaucratic" H<1 naming criterion (though they didn't give a scientific reason for the declaration either, AFAIR). Why do you think Haumea's DP status to no longer be secure? It's true that it's not larger than former-HE Iapetus, but unlike with Iapetus, we do know that Haumea does rotate fast enough for its estimated shape to still be in equilibrium. And unlike a moon, it shouldn't have changed its rotation period substantially over time (after its presumed past massive collision, which should have melted it). --Roentgenium111 (talk) 19:20, 25 June 2014 (UTC)

We meet this problem on Simple too. ONaNcle (talk) 08:56, 28 September 2016 (UTC)

HE2

We need the ref that Iapetus is not in HE. — kwami (talk) 22:52, 11 April 2014 (UTC)

Here's Lakdawalla mentioning it. There's also an article in Icarus. Tbayboy (talk) 00:08, 12 April 2014 (UTC)

Thanks! — kwami (talk) 04:26, 12 April 2014 (UTC)

Possible typo in dimensions of equatorial ridge

The dimensions given for the ridge give a height of 14 km and width of 20 km. These numbers are inconsistent with the profile photo showing the ridge outlined against the black of space. The side-slopes of the ridge on that photo reveal a relative proportion of width to height on the slopes more on the order of 2:1 at that location. The shot is slightly oblique to the ridge trend, which causes an apparent flattening of the slope in the photo relative to actuality, but this would be a slope angle between 27° and 35°. I don't know what the properties of ice would be at that temperature, but that would be a reasonable friction angle for granular particles. The strength of gravity would not matter as the stable slope of a purely frictional granular material is determined by a frictional coefficient times a ratio of vector components of its weight resolved both parallel and perpendicular to the slope, so the gravitational coefficient is in both numerator and denominator and cancels out.

Allowing for the flat area on top, the total width looks to be about 5 or 6 times the height. A height of 14 km would have a base width of 70 to 84 km at the location of the profile on the photo. Please check the original articles for the correct values. In an article in http://phenomena.nationalgeographic.com/2014/05/30/saturns-moon-wears-the-weirdest-mountain-range-in-the-solar-system a width of up to 200 km is given, which would presumably apply where the triple-width ridge mentioned in your article occurs. Tony Cooley (talk) 02:08, 31 May 2014 (UTC)

Is Iapetus the only large moon from which the rings of Saturn would be clearly visible?

Extraterrestrial skies#The rings from Saturn's moons seems to be saying that Saturn's rings would also be visible from Mimas and Tethys. (As well as Janus and Epimetheus, but they're not really large moons.) Double sharp (talk) 12:43, 31 May 2014 (UTC)

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Adding surface gravity and fraction of Moon's gravity

I am adding the surface gravity and percent of Earth's moon gravity in the format as used on Titan (moon).

• Surface gravity: Given the gravity calculation of 0.223 m/s2 and Gravity of Earth set to 9.80665 m/s2: acceleration would be 0.223 / 9.80665 or 0.022797 rounded to (0.00228 g)
• Percent Moon's gravity: Given the Moon's gravity of 1.62 m/s2 (0.1654 g), moon multiplier would be 0.223 / 1.62 or = 0.13765 rounded to (0.138 Moons)
• Check: Iapetus's surface gravity calculation (above): 0.022797 g / 0.1654 g = 0.01378295

Appears in order, so changing:

• | surface_grav = {{Gr|1.805|734.5|3}} [[Acceleration|m/s²]]
  

to

• | surface_grav = {{Gr|1.805|734.5|3}} [[Acceleration|m/s²]] ({{val|0.00228|u=[[G-force|''g'']]}}) (0.138 [[Moon]]s)
  
• Compiled: surface_grav = 0.223 m/s² (0.00228 g) (0.138 Moons)

2606:6000:CB81:1700:201B:37B8:E9F7:6142 (talk) 23:24, 17 September 2019 (UTC)

Iapetus Inclination Given is Wrong (According to Source) and Confusing

As per the source given in the article's sidebar, https://ssd.jpl.nasa.gov/sats/elem/#saturn, the inclination given for Iapetus is slightly off. The sidebar states an inclination relative to the Laplace plane of 8.13 degrees. The NASA source states that the inclination relative to the Laplace plane is 7.6 degrees. Close, but imprecise. Perhaps this is coming from another source, as this is relatively close, and inclination relative to the Laplace plane would vary a little over time due to perturbations. Furthermore, the sidebar states that the inclination relative to the Saturn's equator is 15.47 degrees. This is roughly the inclination of Iapetus's Laplace plane relative to Saturn's equator. This is technically correct no matter how you interpret this, because the 'average' orbit of Iapetus over an entire period of precession will be equal to the Laplace plane. However, this may be confusing or subject to misinterpretation for those unfamiliar with the concept of the Laplace plane, as the inclination of Iapetus is time-variable with respect to Saturn's equator, depending on the longitude of the ascending node, and with maximum value equal to the sum of Iapetus's Laplace plane's inclination and Iapetus's inclination with respect to the Laplace plane, and a minimum value equal to the inclination of Iapetus's Laplace plane with respect to Saturn's equator minus the inclination of Iapetus's orbit with respect to the Laplace plane. — Preceding unsigned comment added by Sciencecompliance (talk • contribs) 19:30, 25 April 2022 (UTC)

As an update, I went ahead and made the changes to the article discussed in the comment for which this is a reply to.

The inclination relative to the Laplace plane has been updated in accordance with the source given above, and the inclinations relative to the ecliptic and Saturn's equator have been changed according to the source and updated to make the inclination referring to that of the Laplace plane rather than an osculating value.

The inclination for the Laplace plane relative to the equator was calculated from the right ascension and declination values given in the table in the above referenced source, and an obliquity of the celestial equator to the ecliptic of 23.4392911 degrees was used to rotate the equatorial-referenced R.A./Dec. Laplace plane normal vector relative to the ecliptic.

Someone might want to check my math as a verification. Sciencecompliance (talk) 20:09, 25 April 2022 (UTC)

Twenty-fourth?

In what sense is Iapetus "the 24th of Saturn’s 83 known moons"? Clearly not by mass or diameter. Date of discovery? Mean orbital radius? Alphabetically? For a statement in such a prominent position, should it not be more clear and relevant?

--~~~~ Seismofish (talk) 10:23, 2 March 2023 (UTC)

Satellites are ordered in distance from the planet. Just like planets are ordered from the Sun. :) Fomalhaut76 (talk) 09:20, 20 April 2023 (UTC)