Talk:Oort cloud/Archive 2

Archive 1

Archive 2

Archive 3

Potential rewrite

I have been reading the literature on the subject and would like to suggest the following rewrite with the aim of getting rid of the tags that are on this section. I could find no citatable sources in support of the idea that the presence of an inner Oort cloud would suggest that the Sun formed near other stars, so have deleted that claim. The table of potential Oort cloud objects could then stand. Please let me know if you have any coments, either here on on my talkpage before I go ahead and edit the article.

So far, only three objects with orbits which suggest that they may belong to the Oort Cloud have been discovered. 90377 Sedna, 2000 OO67 and 2000 CR105 have orbits which, unlike those of the scattered disk objects, cannot be explained by perturbations of the main known planets and may thus constitute an 'inner' Oort cloud. Their orbits can then be explained by one of two theories. Either these objects were Oort cloud bodies disrupted by the passage of a neaby star close to the solar system (Morbidelli and Levison (2004)), or else their orbits were disrupted by an as yet unknown planet-sized body within the Oort Cloud (Gomes et al. 2006) .

Chrislintott 18:50, 12 May 2007 (UTC)

Changed in face of overwhelming indifference Chrislintott 07:14, 17 May 2007 (UTC)

PR

Some suggestions:

• The lead section isn't really a summary of the article; it introduces a number of facts that are not covered in more detail later. (C.f. WP:Lead.) Perhaps most of the lead should probably be moved down into the main article?
• Comet Halley is actually a short-period comet. —Preceding unsigned comment added by 128.123.86.125 (talk) 00:40, 25 February 2008 (UTC)
• The SolStation article has some references that may be useful. That article also includes information about interactions with giant molecular clouds and galactic tides.
• The Dave Darling site suggests some recent work about asteroids in the Oort cloud.[1]
• Perhaps something could be added about numerical simulations of the cloud formation?[2][3]
• Other interesting sources:

http://adsabs.harvard.edu/abs/2006Icar..184...59B

http://home.xtra.co.nz/hosts/Wingmakers/The%20Oort%20Cloud.html

Thanks. — RJH (talk) 18:26, 19 May 2007 (UTC)

I've done as much as I can. I'm only a layman so I'm not really qualified to go any deeper than I have. Is there anyone out there who could take this on? Serendipodous 17:08, 27 May 2007 (UTC)

No offense, but it's usually appreciated when the person nominating an article for a PR also has a go at addressing the issues raised. — RJH (talk) 16:30, 1 June 2007 (UTC)

Sorry, but what? I added info from all those links into the article. A lot of it may have been taken down by Ruslik when he did his rewrite, but most of the refs are still there. Serendipodous 16:35, 1 June 2007 (UTC)

I guess "never mind" then. Thanks. — RJH (talk) 19:33, 9 June 2007 (UTC)

GA Passed

This article easily meets GA requirements. It is well written, informative, and covers the topic well. It uses good sources and the liberal use of inline citations makes it easy to verify. The illustrations are appropriate, informative, and have aprropriate copyright status. They are also quite attractive. The Lead is appropriate for an article of this length.

I do have a couple of quibles however. The article has a couple of red links (one in the article itself and one in a footnote). This is always annoying. I would suggest either creating the appropriate articles or removing the links if nobody is going to get that in the immediate future. You can always add the links back in when the articles are created. The final section mixes inline citations (footnotes) with Harvard style citations (like (Gomes et al. 2006)), and worse the inline citations and the Harvard style citations appear to be duplicates. I suspect this happened because the editor liked the fact that the Harvard style references meant the name of the author making the claim appeared in the text rather than in a footnote, but if that is the case you should mention the paper and author in the text directly. What you have now makes it look like you are citing two separate sources when in fact you are not. These are minor concerns for an otherwise excellent article. Rusty Cashman 22:11, 27 May 2007 (UTC)

Oort cloud vs. Scattered disc

As I understand it, what makes Sedna special is not its aphelion but its perihelion. At 76 AU it never comes close to Neptune in its orbit, and therefore could never have been scattered into a higher orbit by Neptune's early migration. The same is true of 2000 CR105 [4]

There's little in the scholarly literature about OO67 or SQ372, but both those objects have perihelia which take them inside Neptune's orbit, which means they could have been affected by Neptune's migration. As such, it seems highly unlikely that either is an Oort cloud object; rather it seems that both of them are merely highly extended scattered disc objects. This article considers OO67 a Centaur.

I will keep things the way they are for three days; if at the end of that time, no one has come up with any verifiable information regarding whether OO67 and SQ372 are Oort cloud objects, I will remove them both from the list. Serendipodous 15:24, 4 June 2007 (UTC)

Time's up. Objects deleted. Serendipodous 12:33, 7 June 2007 (UTC)

Listing any, or only two objects here seems arbitrary. The objects listed (plus others) are classified under slightly differing (Detached, Scattered-Extended etc) terms depending on the source. See related section of scattered disc article with multiple references including DES classification. Eurocommuter (talk) 20:59, 5 December 2007 (UTC)

The two objects have been described as possibly being Oort cloud objects. The region to which they belong is unmapped, so its extent and structure are currently unknown. They are, however, the only two objects that could be Oort cloud objects, even if they aren't. Serendi^podous 23:24, 5 December 2007 (UTC)

Dubious Reference I Found

I was looking online for some more information/references to use in the article, and I found a NASA site that has some odd claims. It says the outer radius of the Oort cloud is 30 trillion kilometers from the Sun (putting it at just over 200,000 AU) and that there's probably enough mass in the Oort cloud to make up 40 Earths or so. This information seems to contradict with what I've read on Wikipedia. I'd brush off the site as being wrong, but this is a NASA site. Is this information outdated, an upper limit, or just plain wrong? --pie4all88 (talk) 21:11, 22 December 2007 (UTC)

Because the Oort cloud is hypothetical, its characteristics have to be inferred from mathematical models, and mathematical models are only as good as the data you put into them. Old data placed the mass of the Oort cloud as high as 300 Earths, but User:Ruslik0 inserted more recent sources that place its mass at just 3 Earths. Since Ruslik is a scientist and uses primary sources, I'd trust his word before I'd trust an old NASA blurb. Serendi^podous 00:02, 23 December 2007 (UTC)

Ok, that sounds reasonable. Thanks for the quick response. :) --pie4all88 (talk) 04:19, 23 December 2007 (UTC)

Oort Cloud in Science Fiction

There has to be a wealth of literature out there set on far off locations in the Oort cloud. It'd be good to have a section in the article page that lists the texts/novels for plain 'ole bed-time reading :=)

One recent series that springs to mind is Abdul Ahad's First Ark to Alpha Centauri (2005), which purports to be the first scientific blueprint for a future human voyage across the Oort cloud. It paints a rather dense picture of Oort clouds surroudning both our own star and the neighboring Alpha Centauri system, that are rich in icy comets and small planetoids and which supposedly overlap in the middle. Hence the need for a virtual bridge type of island hopping to go across in a cylindrical ark ship of the far distant future. Worth a strong read by Oort cloud enthusiasats here imho ;=).

90.193.170.74 (talk) 19:12, 1 January 2008 (UTC)

Clarification

I think we need to specify where we think the Oort cloud begins and ends. Does it begin at 50,000 AU? Does it end there? if it starts at 50K AU, does it extend to the very edge of the Sun's Hill sphere (maximum extent of gravitational pull), at roughly 125,000 AU? I think this is something that needs to be explained. RingtailedFox • Talk • Contribs 20:30, 24 January 2008 (UTC)

It's frustrating. I plugged a number of values in AU into Google Scholar, filtered for recent articles, and got everything from 50,000 to 200,000 AU for its aphelion. I even got one article saying that the Oort cloud began at 50 AU, which is rather odd. The most oft-cited figure is 100,000 AU, but that seems pretty vague. I think the short answer is nobody has a clue. Serendi^podous 23:06, 24 January 2008 (UTC)

My bad there at the starting point. I was formatting and got an edit conflict and that value slipped through my merge :) Samuel Sol (talk) 17:12, 18 March 2008 (UTC)

Road to Featured Article

Very well, after talking to serendpious, we decided to tackle this baby to FA status. I will start with re-writing and copyediting what we have. The article does look a bit short, I'm not sure if it is the lack of sources or that it has to be expanded. We should look at Kuiper Belt, since it is similar to the Oort Cloud as a comparison, I think. Samuel Sol (talk) 13:57, 14 March 2008 (UTC)

I just merged some info from some other articles that refer to the Oort cloud but which this article was, oddly, missing. I have some personal sources I can employ, which I will begin to consult today. I have placed a two day order for some books at my local library, which should be available by Tuesday. Serendi^podous 09:19, 16 March 2008 (UTC)

I'm going through the list of sources already in the article, and the papers I cannot access through here I will try to see if I have access here at the University. If so I will get those and try to consult. Samuel Sol (talk) 14:14, 18 March 2008 (UTC)

Is it possible to expand this article much more given the hypothetical nature of the Oort cloud? You might be in danger of mis-representing postulations as facts. AstroMark (talk) 21:45, 24 March 2008 (UTC)

Origin

I started reading this source yesterday and will do a rerun on it before adding anything. But on the topic of the Origin of the Oort cloud it proposes that the formation would be tied to giant molecular clouds and accreation(sp?) from the jovian planets. Since this is far from my area of expertise, do you think it merits more mention? If so, when I get home tonight I will work on wording it. —Preceding unsigned comment added by Samuel Sol (talk • contribs) 12:16, 19 March 2008 (UTC)

For an FA Push...

I have garnered a list of things that this article might need. Feel free to add on.

List:

• More references

* Additional information-however, not unecessary information-I mean expanded!

• Images

• Some bold work!

Good luck! Come on guys, with Samuel Sol and Serendipous leading us, we can do this!

Thanks,

Meldshal42_{Comments and Suggestions}^{My Contributions} 20:52, 20 March 2008 (UTC)

Distance from the Sun

I read in the following article here-[5]- that the sun is not one light year away, but approximately 3 light years away from the sun. This is from the same source that I put the reference I just added. Just wanted to confirm it. I will add it to the article, remove it if it is incorrect.

Can't read it. But make sure that the figure is radius and not diameter. Serendi^podous 21:04, 24 March 2008 (UTC)

The actual link is [6]. This does mention a radius of 3 light years however this does conflict with the 50,000 AU given at the start of the article so should not be placed there. It does agree with the upper limits given later on in the article - although 3 light years is more than half the distance to the nearest star, it is possible that our Oort cloud overlaps with a neighbouring Oort cloud since the clouds are so sparsely populated. AstroMark (talk) 21:35, 24 March 2008 (UTC)

That makes sense. Thank you.Meldshal42_{Comments and Suggestions}^{My Contributions} 21:37, 24 March 2008 (UTC)

You need to read this [7] (ref 1 in the article). And if you not satisfied you can go through the long reflist of this publication. Ruslik (talk) 06:47, 26 March 2008 (UTC)

Extension from the Sun

Please excuse me-I have been looking up possible links for references. Is it true that the oort cloud extends 30 trillion kilometers from the sun as said here( this is a more reliable resource obviously)? [8]

Thanks, Meldshal42_{Comments and Suggestions}^{My Contributions} 00:24, 25 March 2008 (UTC)

30 trillion km is 200,000 AU, which is the maximum distance given in the article, so it does fit. The problem, which was raised here, was that there isn't a universally agreed limit to the radius of the Oort cloud, and different sources will give different figures. Serendi^podous 18:12, 25 March 2008 (UTC)

The biggest problem is the since the cloud is still hypothetical, people can only predict how long it actually is. And until some direct measures is taken, we will have different astronomers with different data. This ref there I've been reading, for example, works with an Oort Cloud of 1000AU to 10000AU (with inner cloud 10³ < a < 10⁴ and the outer 10⁴ < a < 10⁵ ). Samuel Sol (talk) 12:21, 26 March 2008 (UTC)

Comets

It seems this section n the article is devoted to comets. I would think that this section would explain about comets in the Oort cloud. I will do this now. Thanks, Meldshal42_{Comments and Suggestions}^{My Contributions} 00:32, 25 March 2008 (UTC)

FAC

Book Citation

I commented this link [9] from the article as it got a bit confusing. The URL goes to one book (The First Decadal Review of the Edgeworth-Kuiper Belt. by J. K. Davis), but the reference data was mixed with the preceding article by Fernandez et al. I formatted the reference for the cite book, but left it commented because I'm not sure which one is correct Samuel Sol (talk) 13:25, 31 March 2008 (UTC)

Another book presented to be a bit problematic, citation-wise [10] and [11]. Copied bellow is the tag I used for it. Basically the problem lies within the authors. Comets II is a compilation book of papers (as much as I could get) and we are citing one of the chapters. Now I'm not sure if the chapter by Dones et al got published as a paper before somewhere and if it would be better to cite that paper if it exists. I'm not sure either if I cited correctly. I hope so. Samuel Sol (talk) 13:33, 31 March 2008 (UTC)

{{cite book |title=Comets II |chapter=Oort Cloud Formation and Dynamics |editor=Michel C. Festou; H. Uwe Keller; Harold A. Weaver |author=Luke Dones, Paul R Weissman, Harold F Levison, Martin J Duncan |url=http://www.uapress.arizona.edu/books/bid1580.htm |chapterurl=http://www.lpi.usra.edu/books/CometsII/7031.pdf |Publisher=The University of Arizona Press |origyear=2004 |accessdate=2008-03-22}}

Reference

I couldn't find this paper, on the reference list, Evolution of the Oort Cloud and Distribution of New Comets Due to the Galactic Tide, A. Higuchi, E. Kokubo, since it is from a japanese paper, I imagine there were some problem on translating the names, and got the other paper by the same two authors that deal with the same subject, and is a good ref to this statement. Samuel Sol (talk) 15:48, 31 March 2008 (UTC)

Question

In one section it says the mass of the outer Oort cloud is not likely to be more than a few Earth masses; the mass of the inner Oort cloud is unknown. Later, it says the mass of the Oort cloud is about 3 Earth masses. This would seem... contradictory. I realize that the first reference, which is cited for the 3 Earth masses claim, does mention that subject to certain assumptions and models one would get the mass of the Oort cloud to be 3 Earth masses, but I don't think that's at all a confident figure. So perhaps giving a specific value like 3 Earth masses is overconfident on our part? Kier07 (talk) 20:21, 31 March 2008 (UTC)

Also, what does "half of objects that are scattered travel outward towards the Oort cloud, just as they are also scattered inward towards the Sun" mean? Does it mean that half of objects scattered from the scattered disc go outward and half go inward? Is this obvious, or does it require citation? I think this sentence should be clarified, anyhow. Kier07 (talk) 20:37, 31 March 2008 (UTC)

I've clarified the scattering sentence. It is cited; the citation in the following sentence cites it. The mass figure is "about three", which I think is a fairly good description, since it could mean anything more than one but less than five. Serendi^podous 10:44, 1 April 2008 (UTC)

Featured Article Criteria

• Before we end up passing or failing on FAC, we should probably review the article over the FA criteria. Please mark done by using the  Done template. So I posted it below:

It is well-written, comprehensive, factually accurate, neutral and stable.

(a) "Well-written" means that the prose is engaging, even brilliant, and of professional standard.  Done

(b) "Comprehensive" means that the article does not neglect major facts and details.  Done

(c) "Factually accurate" means that claims are verifiable against reliable sources and accurately represent the relevant body of published knowledge. Claims are supported with specific evidence and external citations; this involves the provision of a "References" section in which sources are set out, complemented by inline citations where appropriate.  Done

(d) "Neutral" means that the article presents views fairly and without bias.  Done

(e) "Stable" means that the article is not the subject of ongoing edit wars and that its content does not change significantly from day to day, except for edits made in response to the featured article process.  Done

It follows the style guidelines, including:

(a) a concise lead section that summarizes the topic and prepares the reader for the greater detail in the subsequent sections;  Done

(b) a system of hierarchical headings and table of contents that is substantial but not overwhelming (see section help);  Done

(c) consistently formatted inline citations using either footnotes[1] or Harvard referencing (Smith 2007, p. 1), where they are appropriate (see 1c). (See citing sources for suggestions on formatting references; for articles with footnotes or endnotes, the meta:cite format is recommended.)  Done

It has images and other media where they are appropriate to the subject, with succinct captions and acceptable copyright status. Non-free images or media must meet the criteria for the inclusion of non-free content and be labeled accordingly.  Done

It is of appropriate length, staying focused on the main topic without going into unnecessary detail (see summary style).

Meldshal42_{Comments and Suggestions}^{My Contributions} 20:41, 3 April 2008 (UTC)

Merge with Hills cloud?

The Hills cloud article is a stub of less than a paragraph in length. It could go in its entirety into the structure and composition section. Serendi^podous 17:35, 1 April 2008 (UTC)

agreed merge and redirect hills to here. Samuel Sol (talk) 17:38, 1 April 2008 (UTC)

Good Luck

Good luck to all the editors of this article. Thanks to you, we are at FAC and will hopefully pass. It has been an honor working with editors of this level. Thank you. This is an excellent article, and no matter what happens, I am proud. Also wanted to notify everyone that i have marked the prose number as done. The work has been excellent, and the effort even better. We have done an amazing job. What can i say? With srendipodous and samuel sol leading us, what else can be expected? It is just as i predicted at the beginning of this process.

Now read this even if you have no obligation to, please.

GO OORT CLOUD ON FA! Meldshal42_{Comments and Suggestions}^{My Contributions} 14:54, 6 April 2008 (UTC)

Congrats! Meldshal42_{Comments and Suggestions}^{My Contributions} 01:13, 13 April 2008 (UTC)

Image of Jan Oort

I was wondering if anyone had a image of Oort or if there was any resource we could use the image from? Thanks, Meldshal42_{Comments and Suggestions}^{My Contributions} 19:26, 1 April 2008 (UTC)

There's one on his bio page, but it's not that interesting. Serendi^podous 21:07, 1 April 2008 (UTC)

2000 CR105 diameter

I am not sure I like the new reference for 2000 CR105's diameter. At VOLATILE LOSS AND RETENTION ON KUIPER BELT OBJECTS 2000 CR105 is listed as 160-253 km in diameter (they assume an albedo of .1 to .25). So if you use a generic albedo of 0.1 you get a diameter closer to 250km. -- Kheider (talk) 00:36, 2 April 2008 (UTC)

OK. Subbed it. Serendi^podous 07:26, 2 April 2008 (UTC)

British/American

I've noted an inconsistency with the use of disc and disk. My English isn't that good so I leave it to someone else to check the whole article for maybe other such problems. Randomblue (talk) 04:38, 4 April 2008 (UTC)

fixed. Serendi^podous 07:49, 4 April 2008 (UTC)

J.G. Hills

Conmsidering he is the man who proposed that the Hills cloud even existed, I think an article should be created about him. I would do it, but I know nothing about him. Meldshal42_{Comments and Suggestions}^{My Contributions} 01:08, 5 April 2008 (UTC)

Dragonriders of Pern

No mention of Pern? Cirt (talk) 09:33, 9 April 2008 (UTC)

What does Pern have to do with the Oort cloud? EDIT: Oh I see. Well, since the Red Star has a 250-year orbit, and Sedna's orbit is 12,000 years, and since the Red Star predates the discovery of Sedna by 30 years, I can safely say that it does not really qualify as an Oort cloud object used in fiction. Given its 250-year orbit, high eccentricity and interaction with the inner planets, the Red Star would be better described as a Centaur.Serendi^podous 11:39, 9 April 2008 (UTC)

Red Star would not be part of the Solar System since it orbits the dwarf star Rukbat (Alpha Sagittarii). It could be a Rukbat Oort Cloud type object depending on rather a 'Turn' year is close to 40 Earth years. Since Rukbat is a dwarf star any planet taking 40 Earth years (a single Turn year?) to orbit would be well outside of the Habitable zone. So it might be better if Red Star with its 250 "Turn/Pernese year" orbit turned out to be more of a planet sized centuar or KBO. -- Kheider (talk) 15:53, 9 April 2008 (UTC)

I mentioned this in the section on the current discussion page but I'm putting it here as well just in case. The books have never suggested that the Red Star originated from the Oort cloud - the cloud becomes relevant because it is revealed in Chronicles of Pern to be the actual origin of Thread. In amongst the ice and rock Anne placed frozen spherical 'pods' of alien mycorrhizoids which become the Thread that falls on Pern as it connects with the atmosphere. Obviously that's fiction and not relevant to the main body of the article but it seems worth adding a section on 'Oort clouds in fiction', especially since I find it hard to believe Anne McCaffery is the only Sci-fi writer to use Oort clouds when almost every other scientific fact or theory has made an apperence at some point. If nothing else it shows an interest outside of astonomers. Danikat (talk) 10:04, 23 January 2009 (UTC)

Proxima Centari May Not be the Closest Star to Our Solar System

The article mentions Proxima Centari as the closest star to our sun. The WISE telescope mission (also known as Wide-field Infrared Survey Explorer) is currently examining 3,000 previously unparallaxed nearby dwarf stars. It's possible one of them could be found to be closer to our solar system than Proxima Centari (hence adding the phrase "currently known" to the related sentence in the article).

198.59.46.5 (talk) 21:54, 8 August 2010 (UTC)

CONGRATS

CONGRATS TO ALL THE EDITORS. THANKS TO YOU WE FINALLY MADE FA. Meldshal42_{Comments and Suggestions}^{My Contributions} 01:18, 13 April 2008 (UTC)

Now that I've calmed down a bit, Congrats. Especially to Serendipodous and Samuel Sol. Great work by everyone. Check out Serendipodous's Vanity closet Thanks, Meldshal42_{Hit me}^{What I've Done} 00:40, 14 April 2008 (UTC)

Anne McCaffrey's Pern?

Anne McCaffrey's Pern books are one of the staples of science fiction, and an Oort cloud plays a huge part in that world. I think it's worth a mention (though perhaps not much more) somewhere in the article. See http://en.wikipedia.org/wiki/Pern#Planetary_system_data for a bit more info. Meichigo (talk) 06:26, 24 April 2008 (UTC)

see here. Serendi^podous 08:58, 24 April 2008 (UTC)

But the previous discussion only covers the Red Star itself. In the (chronologically) earlier books Anne specifically states that whilst the Red Star is believed to be a comet that did not form as part of the Rukbat system but was later trapped by the suns gravity the Thread itself originates from an Oort cloud which the star passes through at one end of its orbit. Obviously the existance of Thread within an Oort cloud is purely fiction (at least I bloody well hope it is) but it could be worth adding an "Oort clouds in popular fiction" section at the end of the article, which is the usual way for Wikipedia to distinguish between factual information and fictional "facts" people may have picked up, and to acknowledge that something has made its way into the realms of human imagination. In either case I think it would be relevant to give the books a brief mention at the end of the article, along with any other places an Oort cloud may have featured. Danikat (talk) 09:52, 23 January 2009 (UTC)

The problem is that this article is about the Oort cloud, while Pern's is an Oort cloud. As we don't have any evidence for Oort clouds in other systems, there's no place to put an "Oort clouds in fiction" section. And anyway, "... in fiction" sections are not well-loved in Wikipedia these days, and usually end up deleted. I don't suppose I can mention the fact that nothing with a 250-year orbit could come anywhere near an Oort cloud.Serendi^podous 12:24, 23 January 2009 (UTC)

It seems appropriate to mention that, Serendipodus. The writers I corresponded with rarely have more than a modest grasp on science, and sci-fi readers don't seem to understand that the author's goal is usually to be entertaining (and selling) before anything. It was always a trying moment at NASA when a visitor treated a project with suspicion because the project's theoretical underpinning wasn't how their favorite author explained the theory (!) And often enough, when authors *do* know the theory, some aspects have to be bent to fit the story. Hence, quoting fiction authors is usually not encyclopedic, in fact, it's often misleading. Alpha Ralpha Boulevard (talk) 14:41, 27 February 2010 (UTC)

Comets "dislodged" by stars/Milky way!?

I find this hard to believe:

"The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars, and of the Milky Way galaxy itself. These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System."

"Milky Way" is especially unbelievable - since distance from Sun to galactic center and from comet to galactic center are essentially the same, the difference is really tiny. It can't change comet's orbit abruptly. Only very, very, very slowly.

"Passing star" I can buy, however, if a star passes at ~1 ly from Sun and really alters orbits of comets significantly, we'll see not one or two, but tens of thousands of comets coming from there. That's not what we see.

And if star does not come as close, we are back at "Milky Way" case - comets are only slightly perturbed.

So, it is either no perturbed comets or very many perturbed comets. The above phrase implies that they are "perturbed" one-by-one, which is IMO impossible.

Unless there are a few largish planets in the cloud too... -- 89.102.207.196

Many comets are on near-parabolic orbits obits and are easily perturbed when they are near aphelion. Many comets could be perturbed at the same time, but they would still come to aphelion at different times, be on slightly different trajectories, and thus return to the inner solar system at different times. When a comet is near aphelion it is moving at its slowest as the Suns gravity is about to reverse the comets direction. -- Kheider (talk) 01:05, 19 June 2008 (UTC)

89.102.207.196 wrote "...however, if a star passes at ~1 ly from Sun and really alters orbits of comets significantly, we'll see not one or two, but tens of thousands of comets coming from there."

I'm just curious as to what empirical data do you have for to support this? meinsla ^talk 15:22, 13 February 2009 (UTC)

New article

http://www.dailygalaxy.com/my_weblog/2008/08/new-discoveries.html —Preceding unsigned comment added by Cmanser (talk • contribs) 06:37, 25 August 2008 (UTC)

Nemesis theory "flaws"

The "star perturbations..." section said the following:

The proposal also has serious flaws. It has been argued that a companion star at such a great distance could not have a stable orbit, as it would be ejected by perturbations from other stars. It also now appears that the apparent periodicity Muller used to calculate Nemesis' orbit was not real but an artifact of his statistical methods.

I decided to remove this part because I found an article written by Muller himself, found here, assessing these "flaws", explaining why misconceptions are common, and citing several papers to refute these flaws. I didn't feel the need to explain all this in the Oort Cloud article itself, but if someone wants to do so, they can check the page I linked to, and the "Stability of the Nemesis orbit" section of this article here. Kreachure (talk) 16:11, 1 December 2008 (UTC)

apparent magnitude

What apparent magnitude do the brightest Oort Cloud objects presumably have ? 149.225.92.119 (talk) 16:51, 27 January 2009 (UTC)

Sedna's a 20th magnitude object at perhelion, considered to be the first object observed in the inner reaches of the Oort cloud.Pomona17 (talk) 16:05, 12 February 2009 (UTC)

Also keep in mind:

• At aphelion (furthest from the Sun) Sedna has an apparent magnitude of about 35.
• Sedna is much closer, larger, and brighter than most Oort cloud objects.

-- Kheider (talk) 16:31, 12 February 2009 (UTC)

Voyager

When would any of the probes in space now (like Voyager 1) enter the Oort Cloud? How long would it take them to get there? —Preceding unsigned comment added by 207.250.21.32 (talk) 23:22, 14 April 2009 (UTC)

~12,000 years. So I'm not looking at my watch. :-) Serendi^podous 13:44, 15 April 2009 (UTC)

But look how fast they're going! I thought they'd be there soon :(

Oh wait, I see... the drawings of the Oort cloud are on a natural log scale. Well, at least we can hope to hear something about the interstellar medium from Voyager. 65.96.130.162 (talk) 04:16, 18 August 2009 (UTC)

The thicker parts of the Oort cloud should be around 20,000 to 50,000 AU from the Sun. Pluto is less than 50 AU. See the Heavens Above website for some estimated distances for the spacecrafts. -- Kheider (talk) 04:22, 18 August 2009 (UTC)

Why can't comets be young...?

Let’s suppose that an inquiring mind reads this article, encounters the “paradox” discussion, and wonders about this: If comets are “fragile” and thus cannot be supposed to have executed lots of orbits of the sun over the last 4+ billion years or so, and thus some sort of “replenishment” mechanism must be contrived to explain why they are still here, wouldn’t it be more consistent with Occam’s Razor to drop the contrivance and just say that comets must be a relatively new addition to the solar system? Oh, let’s say, in the last few tens of thousands of years or so? Wouldn’t that be a perfectly reasonable first thought, especially among those who have not been indoctrinated...oops, I mean educated, about these things? The resolution of the “paradox” becomes very simple; there is no paradox, because comets are (relatively) young.

No way; that’s simply not possible, you say. Hmm, well, why not, exactly? Just for grins let’s speculate that comets were produced by some violent event in the solar system several thousand years ago. That’s a far simpler explanation than the “Oort Cloud” and, like it or not, would make a whole lot of sense to a whole lot of folks, some of whom might even be reading this article. Granted, we’d need to explain what that violent event was, and how it happened, and make sure it didn’t violate any natural laws (nothing “super”natural about it). But not knowing the specific celestial mechanics of that hypothetical event is of course not a proof that it didn’t, or couldn’t, happen.

So, would someone be so kind as to provide some references/links to materials that demonstrate via celestial mechanics, analytically (not just by declaration or assumption), that comets cannot be recent additions to the solar system? And shouldn’t a few words be added to this Oort article along these lines, with refs that specifically substantiate this implicit, unstated assumption that comets are not recent, by demonstrating (not simply by assuming) that they are very, very old and so need to be replenished. Thanks, and regards.Rb88guy (talk) 00:34, 20 August 2009 (UTC)

What form would such an event take? Oort cloud comets have an isotropic distribution; they come from every corner of the sky at random. Were they all produced in a single cataclysmic event, they would all have a common source, and so would cluster in a certain part of the sky, like Kuiper belt comets do. Unless the Solar System was, at one point, surrounded by a massive shell of ice 2 light years across which somehow fragmented, I don't see how a cataclysmic argument could be made. Serendi^podous 05:43, 20 August 2009 (UTC)

Well, ok, agreed, it’s difficult to see what that hypothetical event might have been, although the solar system is nonlinear, and chaotic. Many solar system interactions are possible not only without violating any physical laws, but indeed possible (inevitable?) exactly because of those laws. Also, just because I don’t know the exact mechanism of my car’s failure to start yesterday does not comprise a proof that it did not fail to start. And I don’t agree, not knowing the mechanics of this proposed planetary interaction, that the resulting fragments couldn’t end up in more-or-less isotropic orbits. That would need some analysis, to see if the observed distribution was dynamically possible.

But be that as it may, that isn’t the immediate issue for the Oort article. If a bright young student reads this article and then asks why the simple (dare I say “obvious”?) explanation, i.e., that comets are “young” isn’t correct, what do we say? Do we respond with what seems to be your argument for old comets, based entirely on isotropism? Is this discussed in detail, published somewhere?

My main point is that shouldn’t there be a sentence or two, with citations, in the article that clearly asserts that comets are not young, and we know this because....??? Isn’t this hidden, implicit assumption (comets are really, really old) worthy of a few words? Indeed, without this assumption the Oort cloud collapses... and this otherwise outstanding article becomes meaningless. Rb88guy (talk) 15:08, 20 August 2009 (UTC)

Rb88guy, is there any academic, peer-reviewed, respectable source on such a theory? Otherwise, we go with scientific consensus; see WP:OR.--Cyclopia (talk) 15:02, 20 August 2009 (UTC)

Please see comments above, that I was adding just as your edit came in...Rb88guy (talk) 15:08, 20 August 2009 (UTC)

Your comment above does not add anything to the discussion; the content you want to add is still "vetoed", let's say, by WP:OR and WP:SYNTHESIS. If what you are proposing (all of it) is a theory with at least some academic support, please add sources and we will welcome the addition. Otherwise it's just an opinion, and as such we cannot put it on the article. --Cyclopia (talk) 18:50, 21 August 2009 (UTC)

SUGGESTED ARTICLE EDIT: Insert after the first paragraph of the Hypothesis section:

An alternative explanation of the “paradox” is that there is no paradox: If it is assumed that comets are a relatively recent addition to the solar system, then their rate of loss is not an issue. They are still here because they have not been around long enough to need to be “replenished” by the Oort Cloud, and so there is no need for the Oort Cloud hypothesis. However, at present there is no known, much less accepted, mechanism, such as an interplanetary interaction (“collision”), that could have created comets in recent (e.g., the last few thousand years) solar system history. Thus the scientific consensus is to assume that comets are of great age [here is where references are needed], presumably near that of the solar system itself, and so the loss rate combined with this assumed great age requires some form of replenishment. Hence, the Oort Cloud.

Or words to this effect, and with some references added. Rb88guy (talk) 17:58, 20 August 2009 (UTC)

Find the sources, and it can go in. If you can explain how a single cataclysmic event could produce a swarm of comets with thousand-year-long, isotropic orbits in less than a million years, I will be very impressed. Serendi^podous 03:21, 21 August 2009 (UTC)

Also, this single cataclysmic event several thousand years ago would have to leave absolutely no other evidence apart from a massive comet disgorgement. I can't wait to see that theory. I think Oort cloud fits Occam's razor better; I'm sure the scientists who developed this theory agree. I have the feeling that if the evidence fit an massive event, there'd be a theory to that effect. Auntie E. 17:16, 21 August 2009 (UTC)

Ok, folks, I added the paragraph. I agree about "What could have done this in recent times?" but all I wanted to get at in the article was an explicit statement of the assumption that comets are very old. Assumptions should of course always be made explicit. Thanks. Rb88guy (talk) 17:23, 21 August 2009 (UTC)

We do not made explicit all assumptions. To make a bit silly but I hope explanatory example: we do not explicitly say that we assume Jupiter to really exist instead of being just a collective hallucination or that there is a "Jupiter conspiracy". That comets are assumed to be old goes without saying with the (most economical) reasoning: the Solar System is old, comets belong to the Solar System, therefore they are old too. Of course if there is massive evidence of a young origin of comets (or any other category of planetary body) the assumption is discarded, but the burden of proof is on who proposes they are young. --Cyclopia (talk) 18:50, 21 August 2009 (UTC)

But Jupiter can be directly observed, in several parts of the electromagnetic spectrum, and its mass has measurable effects on spacecraft passing in its vicinity. This direct evidence would quickly dispose of arguments that said it wasn’t really there. By contrast, to my knowledge there has been no direct measurement of any comet’s age. Even if we managed to grab a chunk of one and found the rocky material to date to, e.g., 4 Ga, that in itself doesn’t prove that the rocky material has been in its present orbit (or rather, been in the Oort Cloud) as something called a “comet” for that length of time. No one knows the age of comets; we assume it. Why isn’t the reader allowed to know that this central issue for the article is based on an assumption?

Further, I completely disagree about the requirement in scientific writing for all assumptions to be clearly presented. Whether material for Wikipedia or a paper for publication, a clear statement of assumptions is just good practice. As Johnny Carson used to say, “If you buy the premise, you buy the joke.” The reader is entitled to know what the premises are. Think of younger readers who don’t know (or assume) everything you know (or assume)... Rb88guy (talk) 18:20, 24 August 2009 (UTC)

I don't get your point. Should we explicitly write, for example, that we assume for physical laws to be the same on Earth and within the Andromeda Galaxy? Or that we assume that dinosaurs had a DNA-based genome? And this for every article? The problem is that the amount of assumptions for every meaningful sentence or article is enormous (Borges said that every sentence implies the entire universe, since it assumes its existence). As for measurements of age of comets, this can be of interest (it is not a measurement but shows that measuring their age is not impossible at all). Moreover a young age of comets would have clear signatures in the orbital parameters of such objects -for example asteroids in asteroid families are known to be young because their orbital parameters are consistent with that of fragments from the disruption of a larger body. As far as I know, no such signature is present in the orbits of comets and as such the most reasonable assumption is that they are old. Again, I can be wrong, but please provide sources.--Cyclopia (talk) 19:07, 24 August 2009 (UTC)

Can’t say that I’m surprised: I see that the edit I made has been deleted, and I’m not going to argue it; with school starting soon I have other fish to fry. Perhaps I have the wrong perspective on Wikipedia articles. I tend to think like a teacher, and to anticipate questions a reader (many times, a younger student, not someone who already has a graduate degree) might have. You cannot tell me that questioning the age of comets is not a perfectly sensible thing for a student to do, after reading this article for an assignment. Think like a student for a moment: Let’s see, (1) comets seem to be “fragile” and are lost from the Solar System on relatively short time scales; (2) they are still here; (3) therefore, obviously, they can’t have been around very long. Why shouldn’t this line of reasoning, naive and silly as it may seem, be anticipated, and answered in the article? To do so, as I attempted to do, is neither “personal opinion” nor “original research.” Oh, well, I tried. Regards. Rb88guy (talk) 18:26, 24 August 2009 (UTC)

Questioning the age of comets is perfectly sensible for a student. It is not sensible for an encyclopedia to include every possible hypothesis on this question. Moreover (this is my own opinion), students should also learn that there is scientific consensus: this does not mean that they have to accept it without question, but, quite the contrary, be aware that there is people who devoted lifes to investigate and challenge this kind of problems and probably studying their attempt at an answer is best to start your further questioning. And finally, yes, to include your reasoning is original research or at least WP:SYNTHESIS. --Cyclopia (talk) 19:07, 24 August 2009 (UTC)

Trans-Neptunian region

Should the Oort cloud be included in the trans-Neptunian region? See the trans-Neptunian object Talk page

The Oort cloud is quite obviously trans-Neptunian from a layman point of view, but one has to see the scientific jargon involved (which I am only marginally aware of). --Cyclopia (talk) 15:59, 28 August 2009 (UTC)

Hey the intro makes no sense

The intro (first paragraph) says the cloud is about a lightyear away. But it also says that the cloud marks the bounds of the gravitational influence of the Sun. Why would the Sun create a cloud of things one lightyear away from itself?? Please correct 79.138.129.212 (talk) 19:49, 16 November 2009 (UTC)

This question is confusing! Please read the article and check out some of the cited refs to see the rationale for the various claims. Are you concerned that the gravitational influence should not extend that far (and why do you think that)? Do you think the Oort cloud is not actually part of our Solar System (and why do you think that)? There are numerous cited refs that support the Oort as being influenced by the Sun and there is nothing further away that is known to be influenced by the Sun, therefore Oort is the outer limit of the known influence of the Sun. Or are you concerned about the sun creating objects so far away from itself? The "Origins" section of the article explains in some detail how Oort got to be where it is. DMacks (talk) 20:14, 16 November 2009 (UTC)

Gravitational boundary is discussed briefly at [12].

It might be more accurate to say, "The gravitational boundary of our solar system defines the limits of the Oort cloud," rather than vice versa. If that is the case, then the Oort cloud extends considerably farther than one light year from the sun. The nearest part of the sun's gravitational boundary is roughly 2.3 light years from Earth, where the gravity of Alpha Centauri takes over. At that point the boundary approximates a hyperbolic bulge away from the sun's zone of influence, since Alpha Centauri is slightly more massive than the sun. The influence of less massive stars, like Barnard's star, Wolf 359, and Lalande 21185, are like hyperbolic indentations toward the sun or perhaps bubbles within the sun's zone of influence. Sirius has about the same mass as Earth so the boundary there is nearly flat. See List of nearest stars[13] to get the distance and direction each. Onerock (talk) 03:23, 28 April 2010 (UTC)

Qualitative and Quantitative nature differs from article

The "3d diagram model" (File:OortCloud P-sys(PNG-fin)1.png) in the Hypothesis section is both qualitatively and quantitatively flawed. "The scale shown indicates an outer boundary of 1,000,000 AU for the outer Oort Cloud. This is almost 16 light years!" See the discussion on the image page.

Author ("Azcolvin429"), please provide an updated illustration, or this diagram will be removed, with respect. Metafax1 (talk) 11:19, 27 April 2010 (UTC)

The maximum extent of influence of the Sun's gravitational field (Hill/Roche sphere) is about 230,000 AU or 1.1 parsecs (3.6 light-years) (Chebotarev1964). -- Kheider (talk) 14:25, 27 April 2010 (UTC)

Exo-comets are everywhere

"More than 90 percent of the observed Oort cloud comets have an extra-solar origin" / Capture of the Sun's Oort Cloud from Stars in Its Birth Cluster -- Kheider (talk) 17:46, 12 June 2010 (UTC)