Talk:Oort cloud/Archive 3

Archive 1

Archive 2

Archive 3

Argument from Ignorance

...Doesn't the whole concept of the Oort Cloud fall under the Wiki definition of "Argument from Ignorance"? >_> ~Dah Cheese —Preceding unsigned comment added by 76.179.137.176 (talk) 03:43, 23 August 2010 (UTC)

The argument from ignorance is "It has never been disproven, therefore it must be true." The key word there is must. "It has never been disproven, therefore it may be true (or in the case of the Oort cloud, very likely is true, given the evidence), is not an argument from ignorance. Serendi^podous 19:48, 23 August 2010 (UTC)

However, it is taught and put forth in particularly this article as binding and very real truth, with no alternative at all proposed or theorized. At least it seemed that way when I read it. ~Dah Cheese —Preceding unsigned comment added by 76.179.137.176 (talk) 01:33, 28 August 2010 (UTC)

The very opening line says, "hypothesized spherical cloud of comets". It then goes on to say it may lie roughly 50,000 AU from the Sun and that there has been "no confirmed direct observations of the Oort cloud". As the modern accepted theory what-else do you want it to say without getting off topic? -- Kheider (talk) 04:41, 28 August 2010 (UTC)

An imaginary cloud of comets is about as scientific as leprechauns. I wouldn't object at all, if not for the heavy handed way the writers make the hypothesis out as if it is a real thing. I suggest editing it with a view to making it seem more like a tidy story, that has no evidence whatsoever, Because that is what it is. —Preceding unsigned comment added by 98.212.63.192 (talk) 19:54, 12 December 2010 (UTC)

It has plenty of evidence. Every long period comet ever observed is evidence for its existence. Serendi^podous 21:04, 12 December 2010 (UTC)

This should be something that will be shortly resolved by advancing capabilities to image and assay in fine detail the matter in the region in question. There needs to be something connecting the hypothesis with current science in the way that Higgs boson has. My sense is that the current text understates the evidence and/or overstates the hypotheticality. 72.228.177.92 (talk) 11:56, 21 February 2011 (UTC)

I know of no telescope even in the planning stages that is powerful enough to observe the Oort cloud. This region will remain hypothetical for the forseeable future; that said, because, as you say, it is still possible to observe it, given adequate technological advances, the Oort cloud remains a falsifiable hypothesis. Serendi^podous 14:28, 23 February 2011 (UTC)

Do you mean optical telescope? I doubt that's the proper instrumentation for this purpose. 72.228.177.92 (talk) 07:18, 25 February 2011 (UTC)

No telescope, no matter what its wavelength, could spot an object the size of Halley's Comet from a distance of 20,000 AU. Serendi^podous 08:08, 25 February 2011 (UTC)

The only reason something like Tyche (planet) in the Oort Cloud would be observable in the infrared is because as a gas giant Tyche generates its own internal heat. -- Kheider (talk) 09:55, 25 February 2011 (UTC)

I presume the imaging in question will use an active signal to detect the matter in question rather than relying on radiation or any other force (other than gravity) of which it (the cloud) is the source. 72.228.177.92 (talk) 09:23, 26 February 2011 (UTC)

Absolute Magnitude

It seems to me that the two normalizations of absolute magnitude can cause confusion. In "Structure and composition" and reference 14, the 1 AU distance normalization is used. Perhaps this could be clarified by stating non-stellar absolute magnitude. Filiulodimeapatro (talk) 04:10, 21 September 2010 (UTC)

Absolute magnitude in this sentence links to Absolute_magnitude#Solar_System_bodies_.28H.29. Ruslik_Zero 15:39, 21 September 2010 (UTC)

Criticism Section

The article needs a little bit of coverage of criticism to insure that it is upholding the principle of scientific falsifiability. My suggestion is below--Novus Orator 03:06, 7 November 2010 (UTC)

Criticism

The Oort Cloud theory, while generally accepted in the scientific community, has come under some criticism. R. A. Lyttleton questioned the procedures behind adopting a comet shell model in a 1974 research paper:

"The procedures adopted as theory for a shell of comets are shown to be invalid. Any plot of numbers of Long-period comets against 1/a will automatically exhibit a peak at small values of this parameter, and cannot be inverted to demonstrate a high volume-density of aphelia in space. The positions of actual aphelion-points show no sign of any concentration at any range. Further, the aphelion-distance undergoes large almost random changes owing to planetary perturbations at each return, and present values can yield no indication of original positions. That a group of some forty, or even twenty, comets selected for other reasons would all be coming in for the first time has such evanescent probability as to be an entirely inadmissible assumption...The plain conclusions emerge that the shell-theory is devoid of any support by facts, and that the alleged shell of comets is non-existent. "-R.A. Lyttleton

Young earth creationist Danny Faulkner claimed that comets should be all gone if the universe is billions of years old:

"Comets are continually being lost through decay, collisions with planets, and ejections from the solar system. If the solar system were billions of years old, then all comets would have long ago ceased to exist if they were not continually being replaced"-(Faulkner 2001).

The article already says that the Oort cloud comets formed at planetary distances and then were sent out into the shell by planetary action. I don't really understand what the difference is. Serendi^podous 07:55, 7 November 2010 (UTC)

What Novus Orator means is that some (such as Lyttleton) view this hypothesis as implausible, and that this fact should be mentioned in the article. CielProfond (talk) 18:41, 7 November 2010 (UTC)

Does it offer an alternative explanation? Plus, that paper is 36 years old; I would prefer a more modern objection, since science tends to reject older hypotheses. Serendi^podous 18:43, 7 November 2010 (UTC)

I'm open to a different critic. All that matters is that a little bit of ink is given to some of the issues with the theory.--Novus Orator 05:40, 8 November 2010 (UTC)

Assuming there currently are any. This guy's ideas may have been thrown out by another paper. Plus, refutation isn't enough in science; you have to offer your own plausible explanation. Does he? Serendi^podous 08:09, 8 November 2010 (UTC)

I will add more quotes from his paper that detail his explanation (See Above)..--Novus Orator 09:02, 8 November 2010 (UTC)

Yes, he makes the case that there is no Oort cloud, but as far as I can tell he makes no case as to how the long-period comets are appearing in our skies. Serendi^podous 09:11, 8 November 2010 (UTC)

I added a quote from Faulkner that gives the Young-earth creationist solution to the problem.--Novus Orator 09:22, 8 November 2010 (UTC)

Uh, yeah. That's why scientists proposed the Oort cloud as a solution to the problem. This is a scientific article. If the only alternative to the Oort cloud is to endorse YEC, then we can't do that, as YEC is not a scientific hypothesis. Oh, and by the way, I typed "lyttleton" and "oort cloud" into Google, and this article, published 3 years later, came up, refuting Lyttleton's assertions. Serendi^podous 09:24, 8 November 2010 (UTC)

Faulkner may not be notable enough, though you might want to actually include a quote from that refutation of Lyttleton at least. It seems that the principle behind this article is that it must exist rather than accepting the unthinkable alternative that the universe is young.:) I'll leave for now (I don't actually edit creation/evolution related articles due to a strong personal bias towards creationism) but I just wanted to bring it up so you guys can discuss it...--Novus Orator 09:45, 8 November 2010 (UTC)

As long as your not an extreme fundamentalist, God can exists not matter how old (or big) the Universe is. I know priests that happily accept and teach the age of the Universe. This is a scientific article that needs scientific explanations. Twenty years from now science may have a better theory, but for now... -- Kheider (talk) 13:56, 8 November 2010 (UTC)

I have problem with "2. Their orbits could have been disrupted by an as-yet-unknown planet-sized body within the Oort cloud.[48]" in the Oort cloud objects (OCOs) section. Given distance from the sun involved and the expected planetary discriminant, The body in question would have to be 4 MJup or greater to have cleared it's orbit, and an outer (super) Jovian has been both effectively ruled out by WISE and that it could not be in a highly inclined orbit or there would be noticeable effect on the other outer system objects. Abyssoft 74.202.23.198 (talk) 21:13, 15 November 2011 (UTC)

The WISE data hasn't been fully released yet, so I wouldn't say it's effectively ruled it out. Serendi^podous 21:19, 15 November 2011 (UTC)

MOND

As I recall, MOND is a fairly contentious hypothesis, and is not accepted by the majority of physicists. This reference to MOND will have to be qualified somehow, and I'm not sure it deserves its own section. Serendi^podous 22:40, 22 February 2011 (UTC)

This should go into a note. In addition, this section does not contain any references that actually discuss Oort cloud. Ruslik_Zero 09:53, 23 February 2011 (UTC)

Then this is OR and should be removed. Serendi^podous 10:14, 23 February 2011 (UTC)

Sorry, the paper of Milgrom (1983) considers solar system tests. So, the section should be made into a note. Ruslik_Zero 16:22, 23 February 2011 (UTC)

I've rephrased the note; however some reference to the experimental validity of MOND should be added. Serendi^podous 16:57, 23 February 2011 (UTC)

Density of Oort cloud

Regarding the image caption change, the surface area of the outer edge of the Oort cloud would be about 30 billion square AU (4 * pi * (50000 AU)^2 ). Even with billions of comets that would be less than one comet per square AU, an extremely sparse density. The image makes it look like you could barely poke your finger into the cloud without hitting a bunch of comets, so I believe that noting that the density is exaggerated is helpful. Miraculouschaos (talk) 04:17, 8 August 2011 (UTC)

The image depicts the entire Oort cloud, which actually contains many billions of comets. Only an infinitesimal fraction of these are shown. The only way the density could be exaggerated would be if the number of spots in the image exceeded the actual number of comets. Density simply refers to the number of comets per unit volume. How the image "looks" is not relevant; in actual fact, the true density is far higher than shown. This might be more obvious if a scale bar were present in the image, along with an indication of the actual size of a comet. WolfmanSF (talk) 05:42, 8 August 2011 (UTC)

Objection against the Nemesis theory.

As I recall in reading what may well have been the original Nemesis theory article in Scientific American nearly thirty years ago, its claim to fame was that it gave AN explanation to the 26 million year periodic mass extinctions of dinosaurs and their friends. Even then its argument was very weak: essentially, it said that any kind of periodic event with a period as long as 26 million years "could only have an astronomical cause".

And straight away there was an objection that an orbit that far away from the Sun would be utterly unstable (by a mechanism such as that described in the "Tidal effects" section of this article) and would not show any kind of regular periodicity. So isn't this Nemesis dude a hypothesis that has been discredited for a long term? Is it therefore really worthy of mention? Old_Wombat (talk) 09:14, 8 August 2011 (UTC)

I have a tendency to agree that Nemesis as defined in 1984 is all but dead. See: Nemesis is a myth (Max Planck August 01, 2011) -- Kheider (talk) 09:36, 8 August 2011 (UTC)

New Section - Are Voyager/Pioneer in or near the Oort Cloud?

Thumbs up on the article reaching FA status, it's a very interesting read. I had a question that I thought I'd post here. Where are the Viking and Pioneer probes in relation to the Oort Cloud and will they reach it eventually? (If so, how long?). I can't quite work it out from the articles as the Viking 2 talk about "...studying the boundaries of the Solar System, including the Kuiper belt, the heliosphere and interstellar space" but this article doesn't mention the heliosphere so I can't quite rationalise the distance.

Thanks for any info you can provide, I read a lot of the astronomy articles on Wikipedia purely as they are very interesting. CaptRik (talk) 15:05, 8 August 2011 (UTC)

The Voyagers will reach the Oort cloud in about 12,000 years. It's WAAY out there. Serendi^podous 15:07, 8 August 2011 (UTC)

Pronunciation is wrong

Could someone add a ː after the vowel? Thanks. I'd do it myself but the article is protected. — Preceding unsigned comment added by 82.139.87.39 (talk) 02:40, 21 September 2011 (UTC)

I hope you're right. Serendi^podous 05:35, 21 September 2011 (UTC)

You might want to take a look at the result. — kwami (talk) 08:26, 21 September 2011 (UTC)

Never mind. They have a 3rd transcription in the OED. — kwami (talk) 08:27, 21 September 2011 (UTC)

The following is confused

"Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud" - the article defines the disc as a component of the Oort cloud.

Oort Cloud: not a mere "hypothesis" to the majority of scientists

I question your (user Serendipodous) use of "hypothetical" when referring to the Oort Cloud, and your systematic deletions of attempts to correct this.

At the very least, you are presenting a one-sided version of the scientific opinions on this matter. All scientists I know and certainly the majority of scientists I have read or heard, consider the Oort Cloud a "real region of space extending thousands of AUs beyond the orbits of known planetary bodies".

While there is no consensus about some of the evidence found of the inner Oort Cloud (object 2006 SQ372, discovered and analysed from 2006 to 2008, being the first with a direct connection to the inner cloud), the fact remains that a significant portion of scientists consider it serious and conclusive. Furthermore, you do not need to actually travel to or be in the Oort Cloud for it to be real - we know of three separate regions of space that are sources of comets, each characterized by what we call the "Tisserand parameter". Calculations give us precise trajectories of the objects considered, therefore finding where they come from is not difficult.

In order for this article to have any validity you ought to either remove the qualifier (hypothetical, which goes against the accepted views among scientists) or, at the very least, refer to it in a different manner (more intellectually honest). "The Oort Cloud, widely believed to be a spherical region of space (though it remains "hypothetical" to a fraction of scientists)..." would be a proper way of introducing the Cloud. There are several descriptions at NASA and ESA webpages which present this view.

— MikeLousado 22:54, 18 April 2014 (UTC+1)

For what it's worth, I second this. RagingR2 (talk) 23:53, 4 February 2016 (UTC)

I think you have the wrong idea about the difference between a hypothesis and a theory. You use words such as "mere" and "serious" in your post. A hypothesis is not somehow less serious than a theory. A scientifically sound idea to explain a phenomena simply is called a "hypothesis" until it has been substantiated by rigorous testing and/or by empirical evidence, at which point it is then called a "theory."

"a phenomena"? 2A01:CB0C:CD:D800:881E:A6AF:CA0:836A (talk) 14:07, 1 April 2021 (UTC)

The Oort cloud hypothesis is an excellent hypothesis that is very scientifically sound and is well accepted by most scientists as the likely explanation for the origin of long term comets. When some sort of empirical evidence is found there are plenty of scientists who will then quickly change to calling the idea a "theory."

BUT, being an excellent hypothesis that most scientists believe is correct does NOT make it a "theory." Please wait for empirical evidence with the rest of us so we can then upgrade it to a theory which may happen soon. Hexakaidecanitarian (talk) 15:12, 10 February 2019 (UTC)

PS you seem to think people Chang it to "hypothetical" because they somehow doubt it exists. I think based on your suggested verbiage for an intro that you believe hypothetical somehow indicates doubt. Most scientists are strongly convinced that the oort cloud is a correct hypothesis. We call it a hypothesis not because if any doubt; we call it a hypothesis solely because have not yet gotten empirical evidence because it is too far away to observe thus we cannot yet call it a theory. Nasal has sent out some satellites that may provide the empirical evidence needed. BTW. When we do have proof of its existance we simply will drop the word hypothetical and just say it's "a cloud which exists." Hexakaidecanitarian (talk) 15:29, 10 February 2019 (UTC)

PPS. I personally believe the Oort cloud exists and I also believe planet 9 exists an is the reason for relatively clear space between the kypier belt and the Oort cloud (2,000-12,000 au). Both planet 9 and the Oort cloud explain things well, but we sadly have no empirical evidence of either thus both are "hypothetical." Hexakaidecanitarian (talk) 15:55, 10 February 2019 (UTC)

We have seen bits of the Oort Cloud alright, so you are plain wrong there. We have not seen all of it, but then we have not seen all of the Earth and last time I looked there were no cranks insisting that our own planet is hypothetical. Please don't take this as a challenge! 81.49.6.122 (talk) 14:35, 1 April 2021 (UTC)

We have not seen ANY of the Oort cloud. We see long term comets. Long term comets are NOT part of the Oort cloud. According to the hypothesis, long term comets once WERE part of the ort cloud, but then got knocked out and are no longer part of the Oort cloud. The Oort cloud is a hypothetical source for long term comets. The comets exist, they are "fact" that is well verified by emperical evidence. We have no empirical evidence of the hypothetical source cloud. Hexakaidecanitarian (talk) 08:32, 20 May 2021 (UTC)

@MikeLousado "or, at the very least, refer to it in a different manner (more intellectually honest). "The Oort Cloud, widely believed to be..."

You said the Oort cloud is something "widely believed to be" That's a good definition of "hypothetical."

At one point the scientific community widely believed an 8th planet existed. They searched for this hypothetical 8th planet. They found it and named it Uranus. Now we "know" it exists. The existance of an 8th planet is now "factual."

Here is a simple list of concepts:

A scientific "theory" is a "model" that explains. A scientific "theory" is never called "fact," it is forever called "theory."

An "object believed to exist" which explains phenomena is a "hypothesis." "Objects" are "hypothetical" when people "believe" they exist and become "factual" when through empirical evidence we "know" they exist.

If we one day send out a probe that photographs and analyzes the Oort cloud, it goes from being a "hypothetical" cloud that most astronomers firmly "believe" exist, to being a "factual" cloud that we "know" exists. Hexakaidecanitarian (talk) 08:55, 20 May 2021 (UTC)

The whole article except for the first sentence and second section ("Hypothesis") assumes the Oort cloud is real. Is this good writing? Grassynoel (talk) 09:07, 26 June 2021 (UTC)

There is no reason to think it is not real. The Oort cloud has passed every test thrown at it. The discovery of objects like ʻOumuamua and 2I/Borisov only add more validity to it. -- Kheider (talk) 12:21, 26 June 2021 (UTC)

Minor planets → objects

The above change got me wondering: Could there be objects that are part of the Oort cloud and are not minor planets? In other words, would a hypothetical brown dwarf or super-jupiter out there be considered part of it? --JorisvS (talk) 16:36, 2 January 2013 (UTC)

Not really. Any more than an airplane passing through a cloud could be considered part of it. Serendi^podous 17:46, 2 January 2013 (UTC)

But think in the opposite direction, size-wise. The bulk of the Oort cloud probably consists of objects that are too small to be classified as minor planets. — Quondum 18:30, 2 January 2013 (UTC)

Like meteoroids and dust? The same would hold for the Kuiper belt and the asteroid belt. --JorisvS (talk) 20:37, 2 January 2013 (UTC)

Mostly comets, I expect. — Quondum 20:46, 2 January 2013 (UTC)

Which are, if far enough from the Sun, minor planets. Most objects in the Kuiper belt are icy and would become comets if brought closer to the Sun. --JorisvS (talk) 21:00, 2 January 2013 (UTC)

Would dust particles also be considered "objects"? --JorisvS (talk) 23:10, 2 January 2013 (UTC)

I see I've been confusing minor planet with dwarf planet, going by the respective articles. I guess we need someone more familiar with the literature, and in particular with the modern accepted usage of the respective terms. I guess a dust particle would be considered an object; whether the average reader would consider it to be a minor planet is more doubtful. — Quondum 05:59, 3 January 2013 (UTC)

Technically an object can not be a listed as a comet until it has been seen to generate a coma (cometary). But in laymen speak I still think it is better to call Oort Cloud objects comets instead of minor planets so that readers such as Quondum do not get confused. All known near-Earth asteroids are also minor planets. -- Kheider (talk) 09:08, 3 January 2013 (UTC)

Even though we should try not to confuse lay readers, we should not blatantly violate scientific usage of terms either (and only in some places, at that! We don't call the majority of KBOs 'comets', even though the majority is just as icy as the majority of OCOs). --JorisvS (talk) 11:34, 3 January 2013 (UTC)

Couldn't we circumvent the issue by phrasing the lead similarly to that of Kuiper belt? --JorisvS (talk) 11:34, 3 January 2013 (UTC)

This certainly has merit. In the interest of accessibility (and in particular the correct interpretation by the typical interested reader), it may be sensible to forgo the brevity of jargon terms (e.g. minor planet) for a more descriptive approach – either by using a jargon term along with its definition in terms of more everyday terms, or by simply using a more involved description. — Quondum 12:49, 3 January 2013 (UTC)

The Oort Cloud a spherical cloud?

I find it difficult to understand how a shell of "icy objects" or any other matter could remain stable over a period of some 15 billion years. It seems to me, that because of collisions and gravitational interaction, the cloud would eventually evolve into a disk, such as that around Saturn. Are there computer models that support the globular cloud idea? Paul venter (talk) 10:19, 15 January 2013 (UTC)

It's only been 4.5 billion years but regardless, the only way it could form into a disk is if it were more gravitationally tied to the Sun. The inner Oort cloud is hypothesised to be disk-shaped. Serendi^podous 10:41, 15 January 2013 (UTC)

I have to disagree with the "only way it could form into a disk is if it were more gravitationally tied to the Sun". Transforming a globular cloud into a disk is clearly a function of gravitational field strength and time - the weaker the field the longer it will take, but all other things being equal, it will happen. Paul venter (talk) 12:21, 15 January 2013 (UTC)

Yes, but if you calculate it, it's like a trillion years or so... which is far longer than it takes for the Oort cloud to be attritted. --JorisvS (talk) 12:35, 15 January 2013 (UTC)

Is that a calculation or a thumbsuck? Serendipodous (just above) states "The inner Oort cloud is hypothesised to be disk-shaped" - an effect which no doubt will move outward in time, but nothing like a trillion years. Paul venter (talk) 14:07, 15 January 2013 (UTC)

I didn't actually calculate it here, just gave a rough, conservative estimate. Similarly long time scales would hold for the inner Oort cloud. The reason that the inner Oort cloud is hypothesized to be doughnut-shaped, like the Kuiper belt, is because of its origins: scattered out of the plane of the Solar System into elongated orbits that are not very strongly affected by the gravity of other stars but still somewhat. The reason why the outer Oort cloud is hypothesized to be spherical is basically that the original doughnut distribution of orbits has been randomized by the galactic tide. --JorisvS (talk) 14:42, 15 January 2013 (UTC)

Yes, the Oort cloud is not nearly 15 billion years old...obviously. You cannot compare it to the rings of Saturn. I think one can compare it to the irregular moons of the giant planets: they too form spheres and are too far from their planet for tidal effects to affect the spherical form. Also, the Oort cloud is not quite stable, nowadays attrition is higher than replenishment, so the number of objects in the Oort cloud diminishes somewhat. --JorisvS (talk) 10:44, 15 January 2013 (UTC)

Glad that is cleared up. Perhaps the article can be amended to include those thoughts. Another issue is that "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 itself". I tried to clarify this but was summarily reverted. The prime moving force here is due to the resultant gravitational fields of stars in the neighbourhood, whether they are "passing" or not is irrelevant. One also must seriously question the magnitude of the gravitational field contribution from the Milky Way which is nothing more than the resultant field of the stars and other matter comprising it. Has a serious measurement of this ever been done or computed from a model? cheers Paul venter (talk) 11:06, 15 January 2013 (UTC)

To appreciate that stars are 'passing by': In about 1.4 million years Gliese 710, a star currently some 64 ly from the Sun (i.e. not really a nearby star today), will pass within about a light-year from the Sun. --JorisvS (talk) 11:52, 15 January 2013 (UTC)

Quite - and in 1.4 million years its effect can be taken seriously - but not today. Paul venter (talk) 12:14, 15 January 2013 (UTC)

No, but that's not my point: Stars have been passing by like that for the past 4.5 billion years. --JorisvS (talk) 12:35, 15 January 2013 (UTC)

I understand that, but why is the article dismissing the effect of stars which at the moment are nearby (and rushing past)? We don't have to wait a few million years. Paul venter (talk) 13:07, 15 January 2013 (UTC)

Is it? These stars are also 'passing by', the only difference with Gliese 710 is that they don't near quite as closely. --JorisvS (talk) 14:42, 15 January 2013 (UTC)

Mentioning only stars that pass by places undue emphasis on the "passing" neglecting to inform the reader that the gravitational effect starts long before the "passing by" stage and carries on long after it has "passed by" - it would improve the article to make this clear by rewording. Paul venter (talk) 14:58, 15 January 2013 (UTC)

Yes, that's where the galactic tides come in. --JorisvS (talk) 15:59, 15 January 2013 (UTC)

Yes, you're probably right - gravitational fields are far too complex a notion for the average reader - 'galactic tides' and 'passing stars' are much simpler cocepts. Paul venter (talk) 17:28, 15 January 2013 (UTC)

Copied from Kheider's talk page: I note with interest your revert of my edit with the note "No, Oort cloud objects do not bounce "star to star"", which was not what I had written. Since the existence of the Oort Cloud is inferred a lot of its qualities are the subject of speculation. The extent of the Oort Cloud around a star (as I understand it) includes the matter at the very limits of its gravitational dominance, a dominance which automatically passes to the next nearest star and its gravitational field. I don't understand why the effects of the "Galactic tide", which I presume to mean the collective gravitational force of all the matter within the Galaxy, should be larger than that of stars in the neighbourhood. My view of the movement of the outermost parts would be more of a slow drift between the stars. I would love to know more about the reasons behind your emphatic rebuttal. cheers Paul venter (talk) 07:59, 15 January 2013 (UTC)

I reverted it because when there is not another nearby star temporarily dominating a given region of the Oort Cloud, the galactic tide can assume dominance when an object reaches the very edges of the Sun's hill sphere. -- Kheider (talk) 12:15, 15 January 2013 (UTC)

The stars Proxima Centauri, and the binary Alpha Centauri AB have a collective mass of about twice that of our Sun, and are all just over 4 light years distant, certainly qualifying as nearby stars, and having a collective Hill sphere radius far greater than the Sun's. Has any study put a definite outer radius to the Sun's Oort cloud, or does it merge seamlessly with the Oort cloud around Alpha Centauri AB? Paul venter (talk) 12:57, 15 January 2013 (UTC)

The size of the Oort cloud around any star is largely a function of the estimated mass of the Milky Way and thus the galactic tide. The hill sphere of Alpha Centauri only affects a small Oort cloud region between the two stars. Any lead that ignores the effects of the galactic tide and numerous passing stars over millions/billions of years is missing the big picture. Objects perturbed form the Oort cloud towards the Sun can take millions of years to get to the inner Solar System. -- Kheider (talk) 15:01, 15 January 2013 (UTC)

If you read my edits with more care I'm sure it will become clear that I'm not suggesting that the effects of galsctic tides and passing stars are ignored, but rather that the text is rephrased to more accurately reflect what is happening so that readers don't miss the Big Picture. And obviously objects perturbed from the Oort Cloud away from the Sun don't even bear thinking about. Paul venter (talk) 17:28, 15 January 2013 (UTC)

OCOs perturbed away from the Sun? They become unbound (rogues). --JorisvS (talk) 18:06, 15 January 2013 (UTC)

"the objects comprising the Oort cloud should experience accelerations of the order of 10^−10 m s^−2" Are you sure about that? I have never seen acceleration measured in inverse seconds squared. Acceleration as I have always seen it is measured in ms^2, not ms^-2. Are you sure it is acceleration? Are you sure you don't have an extra -? — Preceding unsigned comment added by 139.195.251.2 (talk) 07:41, 23 April 2013 (UTC)

No, the unit of acceleration is m/s², which is m·s⁻². Compare the unit of velocity: m/s = m·s⁻¹ (which is not m·s). --JorisvS (talk) 09:34, 23 April 2013 (UTC)

Where in all did you ever see acceleration expressed in ms^2? Remember, velocity is the derivative of displacement with respect to time, which is how you end up with per second (I do hope you agree that speed is in meter per second, not times second). Entirely analogously, acceleration measures how quickly velocity changes, so you take another derivative with respect to time and end up with another per-second. F = ma so force is in newtons and a newton is a kilogram times meter per second-squared. 81.49.6.122 (talk) 14:32, 1 April 2021 (UTC)

Inconsistency in sentence

The article states, "Analysis of the carbon and nitrogen isotope ratios in both the Oort cloud and..." implying that the Oort cloud is a known entity whose properties are being currently directly measured, yet the beginning of the article states that the Oort cloud is hypothesized. I would think the sentence should perhaps be re-written to indicate that these measurements are thought to be from the Oort cloud, although the existence of the Oort cloud has yet to be proven.

Laurence Klein LaurencKlein@gmail.com — Preceding unsigned comment added by 65.210.59.130 (talk) 13:58, 9 October 2013 (UTC)

Revised. Serendi^podous 14:36, 9 October 2013 (UTC)

Moved from article

Aside from the incorrect formatting of references, can Zachariah1978's contribution be properly integrated into this featured article with less soapboxy-sounding text?

It should be noted that no one has ever actually detected the Oort cloud with a telescope or any other sensing device. "Many scientific papers are written each year about the Oort Cloud, its properties, its origin, its evolution. Yet there is not a shred of direct observational evidence for its existence.” Sagan and Druyan, p. 210. However, Sagan and Druyan believed that the Oort cloud exists, and went on to predict (p. 211) that “with the refinement of our scientific instruments, and the development of space missions to go far beyond Pluto,” the cloud will be seen, measured, and studied. Also, there are critical mathematical errors in the theory which led to the misplaced belief that a cloud of cometary material, called the Oort cloud, surrounds our solar system. Raymond A. Lyttleton, “The Non-Existence of the Oort Cometary Shell,” Astrophysics and Space Science, Vol. 31, December 1974, pp. 385–401. Assuming the Oort cloud exists helps preserve the belief in a multibillion-year age for the solar system. u “Recently, Lyttleton (1974) confirmed our conclusion of 1954: the Oort’s hypothetical cloud of comets cannot exist.” S. K. Vsekhsvyatsky, “Comets and the Cosmogony of the Solar System,” Comets, Asteroids, Meteorites, editor A. H. Delsemme (Toledo, Ohio: The University of Toledo, 1977), p. 470. Vsekhsvyatsky estimated (p. 470) that considerably more than 1020 gm/yr of cometary matter are lost from the solar system. Over the supposed age of the solar system (4.5 billion years), lost comet mass would “nearly correspond to the total present mass of the planets.” He believed this was unreasonable. “... many people would be happier if there were more objective evidence for the reality of the Oort Cloud.” John Maddox, “Halley’s Comet Is Quite Young,” Nature, Vol. 339, 11 May 1989, p. 95.

--NeilN ^{talk to me} 04:13, 15 December 2013 (UTC)

I'm not sure what you mean by soapboxy-sounding text. It is only recently that I learned about this Oort cloud hypothesis. I checked out some of the lines in that block of text and they all point to creationist websites (Young Earth Creationists, YEC). The issue seems to be on the same playing field as radiometric dating vs creationism and evolution theory vs creationism, junk DNA vs creationism, abiogenesis vs creationism, Big Bang Theory vs creationism, Plate Tectonic theory vs creationism, etc. There isn't anything fantastic about the Oort cloud proposition but for some people, it is a very difficult proposition to accept due to religious reasons. Vmelkon (talk) 01:06, 10 December 2014 (UTC)

The text is arguing for the creationist position. Apart from which, crank positions are generally not included in main articles, because doing so wildly unbalances the article. Anybody who could realistically be considered a reliable source of information on the Oort cloud will assert that it exists (and hell, we have directly observed it, but only the small amount close to the Sun. We've only observed the surface of the Earth (well, plus down a few holes), but we don't mention in the Earth article that some people might believe the Earth doesn't exist, or whatnot. WilyD 11:06, 10 December 2014 (UTC)

Please WilyD, don't give them any ideas! 81.49.6.122 (talk) 14:26, 1 April 2021 (UTC)

"Nearly all isotropic"

From the Hypothesis section: "There are two main classes of comet, short-period comets (also called ecliptic comets) and long-period comets (also called nearly isotropic comets). Ecliptic comets have relatively small orbits, below 10 AU, and follow the ecliptic plane, the same plane in which the planets lie. Nearly all isotropic comets have very large orbits..."

Although it's been there a long time, I suspect that the word all should be deleted from the second sentence here, but I don't know enough about astronomy to be sure. From the context I think the phrase "Nearly isotropic comets" is intended. Dave.Dunford (talk) 14:53, 14 February 2014 (UTC)

It says that long-period comets are also called "nearly isotropic comets", because their distribution is nearly isotropic in the sky. It seems it was originally "All nearly isotropic comets ..." and that it was changed when it was misinterpreted as a grammatical error. Saying "nearly isotropic comet" a bit illogical anyway, because there is nothing isotropic about each of these comets individually. "Long-period comets" is logically more precise anyway. --JorisvS (talk) 16:26, 14 February 2014 (UTC)

Oort clouds around other stars

Some of the talk above refers to Oort clouds around other stars. The article does not mention this, so is the theory applicable to other stars, and so should be included? John a s (talk) 22:01, 18 February 2014 (UTC)

There's no reason to assume that other stars do not have Oort clouds; however, since we haven't even found ours yet, it's a bit too early to speculate. Serendi^podous 22:03, 18 February 2014 (UTC)

Since other stars likely have comets, other stars likely have Oort Clouds. -- Kheider (talk) 22:12, 18 February 2014 (UTC)

New telescopes will be looking. -- Charles Edwin Shipp (talk) 19:11, 8 May 2014 (UTC)

There're two very recent papers on Oort clouds around other stars ( http://arxiv.org/abs/1404.3213 ) and ( http://adsabs.harvard.edu/abs/2014arXiv1409.7691V ); and some older work ( http://adsabs.harvard.edu/abs/1998ApJ...501..357P & http://adsabs.harvard.edu/abs/1990Natur.345..305S & http://adsabs.harvard.edu/abs/1986ApJ...302..462A ). I'm not aware of any work specifically about Oort clouds around Main sequence stars. WilyD 13:27, 27 October 2014 (UTC)

Hazard to future travel

We'll just wait and see whether the "nonsensical OR ignorant of the vast amount of space" claim in the article edit history turns out to be accurate. Given the sheer number as well as the size of objects of which they seem to be ignorant (have you read the article? I guess not), regardless of the amount of space between, probability says it is highly plausible and it's just going to happen. Any thoughts, please?

I accept the need for verifiable content, but one cannot just remove stuff because, to them, it is "nonsensical or ignorant."—An Sealgair (talk) 09:03, 19 February 2015 (UTC)

OK, let's do the math: Let's assume that the Oort cloud is at its closest (and therefore densest) probable distance of 0.8 ly. Let's make the (absurd) assumption that every Oort cloud object is the size of Pluto. Let's also round up insanely and say there there are about a quadrillion Oort cloud objects out there, and that they are all at 50,000 AU. A sphere with a radius of 0.8 ly means a surface area of 8.04 ly^2, which is 7.19814558 × 10^26 km^2. Pluto has a radius of 1184 km, which means it has a cross-section of 4,404,060 km^2. Multiplied by 1 quadrillion and you get 4.4040605*10^21 km^2. Even with this absurd setup therefore, a spacecraft would have about 1 chance in 200,000 of hitting anything. The fact that most Oort cloud objects are not going to be the size of Pluto but more likely the size of Halley's Comet would push that chance up to about 1 in a billion. And that's assuming they're all in one sphere; the real Oort cloud is likely to be 50-100,000 AU in radius.Serendi^podous 09:14, 19 February 2015 (UTC)

Re: your addition. Yes we can, and we do, remove content because it is nonsensical and ignorant. Hence why creationists don't post here anymore. Serendi^podous 09:29, 19 February 2015 (UTC)

The asteroid belt is ten thousand times less mass in about a trillion times less volume; you can ballpark that voyager, pioneer, etc. were about a hundred million times more likely to be destroyed crossing the asteroid belt than the oort cloud. It's actually worse, because collision velocities are higher in the asteroid belt, but no matter. The way we avoid destructive collisions between probes and asteroids is to not worry about it, since it's so unlikely. So no, you'll never find a reliable source for collisions in the oort cloud. Although in this paper [1] Roman and his student argue it's plausible for Oort cloud comets near the inner edge of the cloud to collide with a timescale of a few billion years. WilyD 09:50, 19 February 2015 (UTC)

This all is exactly why I removed it as "nonsensical OR (that is) ignorant of the vast amount of space". The vastness of space is beyond anything human minds can comprehend. Only by actually doing the math, we can know the facts. --JorisvS (talk) 11:56, 19 February 2015 (UTC)

The thing about space is that there's so much of it and it's almost completely empty. Jonathunder (talk) 23:08, 19 February 2015 (UTC)

Yep - intuition always leaves us high and dry when a very small number is to be multiplied by a very large number. There is a weird irrational tendency to assume in such cases that the product must roughly be of order one. If you look out for this particular cognitive bias, you will encounter quite a few examples. (One example: there are quite a few fossils - enough to give us an idea about the evolution of life on Earth - and also, there are almost no fossils - the probability of any given organism (or even entire species!) leaving a fossil is exceedingly small.) 2A01:CB0C:CD:D800:881E:A6AF:CA0:836A (talk) 14:14, 1 April 2021 (UTC)

100,000AU

For too long this article has been claiming that the Oort cloud only extends to 50,000 AU. If a=50000AU, Q can equal 100,000AU. The Oort cloud easily extends to 70,000+ AU from the Sun. And as objects are perturbed outward, they can be perturbed back inwards by other passing objects and galactic tides. The lower-density transient edges of the Oort Cloud could easily extend 120,000+ AU from the Sun as it can take millions of years for an object to leave the vicinity of the Sun. It might be time to find a more recent (more direct) source than 2005. The Sun has been swapping Oort cloud material with other stars for billions of years. -- Kheider (talk) 10:14, 19 February 2015 (UTC)

Is that maybe the dominant process out there: swapping Oort cloud material that typically remains far from the stars? If then an object is perturbed inwards it may have been swapped between Oort clouds (or should is it maybe closer to a vast continuous distribution of minor bodies?) for a long time.

Is the ejection ratio of objects (of all stars) consistent with the upper limit to the density of interstellar comets? --JorisvS (talk) 12:05, 19 February 2015 (UTC)

Material bound to the galaxy but not to the Sun encounters the Sun with relative velocities of tens of kilometers per second. The galactic tide and stellar flybys won't be able to bind it to the Sun; barring extremely close encounters with the planets, it will sail in and sail out without any howdy doody. Levison has a paper about grabbing comets during cluster dissolution, when relative velocities are much smaller (though no one has followed up on it, and I ain't sure even Hal believes it). We don't know anything about Oort clouds around other stars (except, perhaps, some unclear information from white dwarfs), so it's unclear how meaningful our knowledge of interstellar comets is (though see Moro-Martin's paper here: http://adsabs.harvard.edu/abs/2009ApJ...704..733M - which I believe is probably the most useful ref for this.) WilyD 13:47, 19 February 2015 (UTC)

I'm not talking about actually capturing interstellar comets that were already not bound to any star (say 'galactic comets' for clarity). We have never observed an object that was on a hyperbolic trajectory (relative to the Sun) before encountering any planets, which sets an upper limit to the density of galactic comets. This is distinct from objects that originated near another star and were scattered into that star's Oort cloud and later came to orbit in the Sun's Oort cloud when its star had a "close" encounter with the Sun (i.e. it was part of the swapped material). --JorisvS (talk) 16:05, 19 February 2015 (UTC)

The considerations for capturing galactic comets or comets from another Oort cloud are essentially identical - both are basically impossible, except for stars that are binaries/higher multiples, or still in the cluster they were born in. Otherwise the relative velocities are too high. WilyD 16:16, 19 February 2015 (UTC)

To capture an external object in the Oort cloud at ~50,000AU from the Sun requires a relative speed to the Sun of less than (0.185 km/s), so now-a-days captures should be rare. But the Sun's birth cluster could have been an orgy where up to 90% of the Oort cloud got swapped. -- Kheider (talk) 17:19, 19 February 2015 (UTC)

2ly

This may be nitpicking, but to say that 100,000 AU is 2 light years, or is half the distance to Proxima Centauri, is a quite imprecise. 100K AU is 1.58 light years. Yes, 2 is the nearest integer to 1.58, but that's still quite a rounding error, 21% off. And Proxima is about 4.24 Light Years away...half would be 2.12. To call 100K AU "half" the distance to Proxima Centauri is an error of more than 25%. Applejuicefool (talk) 15:23, 7 July 2015 (UTC)

That'd only be true if we were talking about 100 000. au, but we're talking about 10^5 au. We know the distance to Proxima quite well for everyday numbers. But we know the outer extent of the Oort cloud pretty well for astronomy numbers - i.e., to order unity. The most recent estimate I'm aware of is http://adsabs.harvard.edu/abs/2013MNRAS.430..403V - but you shouldn't believe it's accurate at the 20% level. WilyD 16:01, 7 July 2015 (UTC)

Sorry, I'm a little confused by your reply. Are you saying that the lines in the article: "...icy planetesimals believed to surround the Sun at a distance of up to around 100,000 AU (2 ly).[3] This places it at half of the distance to Proxima Centauri..." are correct because of the uncertainty in things such as the actual boundary of the Oort Cloud, and the actual distance to Proxima Centauri? That's not really my main point here. The article implies that 100,000 AU (not 10^5, according to the article) is the same thing as - or at least "around" - 2 light years. It's not. You might be closer to a point with the "half the distance to Proxima" thing, but still 25% is *way* off, whether you're talking everyday numbers or astronomy numbers. Applejuicefool (talk) 19:15, 9 July 2015 (UTC)

There is no clean boundary to the outer Oort cloud. It will simply become more diluted as you get further from the Sun. Proxima Centauri is 4.24 ly (268,000 AU), so 100,000-120,000 is very crudely half that distance. Using 2 sigfigs with a conversion of 100,000 AU (1.6 ly) may make the reader think the boundary is better determined than it is. -- Kheider (talk) 19:50, 9 July 2015 (UTC)

Apart from the primary discussion of the Oort Cloud for a second, the article strongly implies that 100,000 AU is the same measurement as 2 light years. That's my main quibble here. 2 light years is ~126,500 AU. 26,500 AU might not be far where you come from, but it's even further than my daily commute, and that's saying something. Applejuicefool (talk) 06:40, 10 July 2015 (UTC)

I see no reason to use excessive sigfigs for an approximation that is only good to the order of magnitude. I have seen people claim that the Oort Cloud extends to 3 ly. Comparing astronomical scales it to your daily commute is just being silly. -- Kheider (talk) 15:40, 10 July 2015 (UTC)

It was a joke. Seeing as this is the Talk page, the only thing silly there is your priggish reaction.2601:41:200:5260:48FA:93CE:7BE7:4789 (talk) 00:01, 14 August 2021 (UTC)

Putting on my professional astronomer hat, yes, 100 000 au is around two light years (though, of course, I'd never use a light year, a hundred thousand au is half a parsec). If we meant 100 000 ± 1, we'd write 100 000. or some such nonsense. (And by writing 2 ly, we mean somewhere between 1.5 and 2.5 ly, or such, so we hit 10^5 au rather easily. We know the size of the Oort cloud to within a factor of three-ish, and the mass to within a factor of ten-ish? Certainly to within a factor of a hundred or so. Order ten percent errors are too small to be concerned about. WilyD 16:00, 10 July 2015 (UTC)

Sig figs

Why are we claiming the outer limit of the Oort cloud is 3.2 ly? Shouldn't we be rounding that to 3 ly using only 1 sig fig? -- Kheider (talk) 05:07, 2 February 2016 (UTC)

Alpha Centauri and the Oort Cloud?

Alpha Centauri system involves a star very much like the sun. If our solar system's Oort Cloud extends to roughly 2 l.y., so roughly half-way to Alpha Centauri, and if Alpha has an Oort Cloud of its own, could it be possible that the two clouds would overlap with one another? 137.205.170.252 (talk) 13:55, 14 July 2015 (UTC)

Probably. But keep in mind that the Oort cloud is very porous and that the Sun makes a close approach to another Star every million years or so. -- Kheider (talk) 14:09, 14 July 2015 (UTC)

I thought the Oort cloud was inside the heliopause? As in, the Oort Cloud is part of our solar system, and the heliopause marks the end of the solar system where interstellar space begins. But that diagram has the oort cloud all the way to Centauri almost. Am I missing something? Leitmotiv (talk) 20:11, 21 July 2015 (UTC)

The heliopause is just where the Sun's solar wind blends into the background. File:PIA17046_-_Voyager_1_Goes_Interstellar.jpg is a Logarithmic scale. -- Kheider (talk) 20:25, 21 July 2015 (UTC)

The heliopause is where the Sun's solar wind is stopped by the interstellar medium (around 120 AU, give or take). This has exactly nothing to do with where objects are still gravitationally bound to the Sun (up to 2 ly / 100,000 AU), which limits the outer edges of the Oort cloud. --JorisvS (talk) 20:30, 21 July 2015 (UTC)

Yup and interstellar medium is further defined as "space between the star systems" but the Oort cloud is commonly referred to as orbiting our solar system... so it seems like a conflict in definitions here. Leitmotiv (talk) 21:54, 21 July 2015 (UTC)

The Oort cloud is largely empty as it is a ridiculously large volume with a radius of 100,000AU. The edge of the interstellar medium is not a decisive boundary. NASA's marketing department should have not have claimed that Voyager has left the Solar System. -- Kheider (talk) 23:23, 21 July 2015 (UTC)

@Leitmotiv: It is the ionic, atomic, and molecular matter that is travelling between the stars, not "the space between the stars". If it weren't for the solar wind, it would reach all the way to the inner Solar System. It has exactly nothing to do with whether bodies are gravitionally bound to the Sun, which is the defining feature of the Solar System: all bodies that are gravitationally bound to the Sun. --JorisvS (talk) 08:50, 22 July 2015 (UTC)

In the 2014 AO for the Discovery program

What does this mean? What is an AO? Should "program" be capitalized? Should there be a wlink for "Discovery" or "Discovery program"? TomS TDotO (talk) 09:26, 16 November 2015 (UTC)

• AO is short for "Announcement of Opportunity" - NASA's jargon for a call for proposals. The link is correct - Programme probably should be capitalised, since it appears to be a proper name, yeah. WilyD 11:34, 17 November 2015 (UTC)

Distance & proposal to split off Hills cloud

Because it seems to be pretty tough to implement the distances in the first sentence (since we only have ranges), should we just leave it in the "Structure and composition" section instead? --AYFKM (talk) 07:52, 2 February 2016 (UTC)

No; as a summary, the lead section should mention the distance range.   ~ Tom.Reding (talk ⋅dgaf)  13:33, 2 February 2016 (UTC)

The lead has to mention some kind of start and end point as that is all the general public probably wants to know. We then need to differentiate the inner torus region from the classic outer spherical region. Part of the confusion comes from calling obejcts like Sedna "inner Oort Cloud" objects. Sedna damn-well is not a classic Oort Cloud object with a>10000. -- Kheider (talk) 14:09, 2 February 2016 (UTC)

When I read the numbers they are confusing to me. We have a range of ranges. To read that the cloud is from X to Y makes me think that that is the extent of the cloud. But no, that is only the estimates of the inner boundary, and it's followed up with "from U to V" as the outer boundary. There cannot be an easy, and simple way of saying it. What we want to get across in the lede is that this is very far from all of the planets and such that we know of, and even far from the Kuiper Belt. We probably want to get the idea that it is maybe more than half-way to the next star. We don't have to go into details. FWIW, I liked the idea of just saying "thousands of AU" ... but maybe adding something like "perhaps as much as 3 light years". And then, later on, get into the details of just how many AU or ly or billions of km, and then one can feel free to be more prolix about the possible boundaries. That's my opinion, but I'm not going to get into an edit war about it. TomS TDotO (talk) 15:05, 2 February 2016 (UTC)

But we should try and prevent readers from confusing the Inner Oort Cloud (Hills cloud) with the more traditional Oort Cloud that is 10000+ AU from the Sun. These regions have undergone different evolutionary pasts. Just because it is confusing is not a reason to ignore the topic. Saying "thousands of AU" is just way too generic IMHO. It might even be time for two separate articles. -- Kheider (talk) 15:21, 2 February 2016 (UTC)

I agree with splitting the Hills cloud and Oort cloud into different articles. Other languages have already so, and they had quite a lot of information for the inner cloud alone.. --AYFKM (talk) 16:59, 2 February 2016 (UTC)

Then the sednoids, Planet Nine, and 2012 DR30 type objects can be discussed in the inner Oort Cloud article while traditional Oort cloud comets with a>10000 can be discussed in the Oort cloud article. -- Kheider (talk) 18:03, 2 February 2016 (UTC)

But if Planet Nine is indeed real, then the existence of the sednoids would be attributable to this planet, not to any of the mechanisms that would create the Oort and Hills clouds (as opposed to objects that remain in the scattered disc). --JorisvS (talk) 11:11, 5 February 2016 (UTC)

Oort Cloud should be capitalized

The title should be "Oort Cloud" with both words capitalized. It is not a 'cloud' in the regular sense of that word, that happened to be named after Oort. Someone decided that "cloud" was the suitable, symbolical term to refer to the sphere of comets surrounding the solar system. Since then, "Cloud" became an integral part of the name Oort Cloud. It is never refered to as the "cloud of Oort", or the "cloud of comets named after Oort", it is always "Oort Cloud". It is the proper name of this phenomenon of which both words are an integral part, so both words should be capitalized. Both NASA and ESA only use the capitalized "Oort Cloud" in their publications. Greetings, RagingR2 (talk) 23:59, 4 February 2016 (UTC)

I agree with you, and the capitalized "Cloud" seems to be used more. But we've also been keeping other astronomical objects, like asteroid belt and scattered disc, lower case. --AYFKM (talk) 12:26, 5 February 2016 (UTC)

You are not wrong, but having been reared on astronomy, the sort of cloud that is the Oort Cloud for me is now included in the regular sense of cloud. Cf. cloud chamber or Cloud chamber? 2A01:CB0C:CD:D800:881E:A6AF:CA0:836A (talk) 14:19, 1 April 2021 (UTC)

External links modified

Hello fellow Wikipedians,

I have just modified one external link on Oort cloud. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://web.archive.org/web/20151117031224/http://whipple.cfa.harvard.edu/inc/documents/Alcock_AGUPoster_2014dec.pdf to http://whipple.cfa.harvard.edu/inc/documents/Alcock_AGUPoster_2014dec.pdf

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 10:18, 21 September 2017 (UTC)

External links modified

Hello fellow Wikipedians,

I have just modified one external link on Oort cloud. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://www.webcitation.org/6H9vGLJk6?url=http://www.swri.org/9what/releases/2010/cometorigins.htm to http://www.swri.org/9what/releases/2010/cometorigins.htm

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 09:26, 29 September 2017 (UTC)

External links modified (February 2018)

Hello fellow Wikipedians,

I have just modified one external link on Oort cloud. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://www.webcitation.org/5x3s4O3KH?url=http://pluto.jhuapl.edu/news_center/news/081706.php to http://pluto.jhuapl.edu/news_center/news/081706.php

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 07:57, 17 February 2018 (UTC)

Updating for 2018: other Oort Clouds?

If you scroll up this talk page you'll see a discussion from 4 years ago about whether to include any discussion about Oort clouds around other stars. I think this should be revisited; even if no Oort clouds have been observed around other stars, stating this would help at least address the question of whether the Oort Cloud is considered a unique phenomenon or now hypothesized as standard around stars (just as a quarter century ago our solar system was the only one known to have planets - now, of course, signs point to exoplanets being common). What is the latest science related to this? Even if all we say is "no one knows yet" that's still relevant to include here because presumably the detection of an Oort cloud around another star would aid in proving the existence of one around ours. 136.159.160.8 (talk) 16:27, 23 March 2018 (UTC)

Do you know any reliable sources? Ruslik_Zero 20:11, 24 March 2018 (UTC)

At the time, I mentioned some:

There're two very recent papers on Oort clouds around other stars ( http://arxiv.org/abs/1404.3213 ) and ( http://adsabs.harvard.edu/abs/2014arXiv1409.7691V ); and some older work ( http://adsabs.harvard.edu/abs/1998ApJ...501..357P & http://adsabs.harvard.edu/abs/1990Natur.345..305S & http://adsabs.harvard.edu/abs/1986ApJ...302..462A ). I'm not aware of any work specifically about Oort clouds around Main sequence stars.

— WilyD 13:27, 27 October 2014 (UTC)

One might also consider this from Scott Tremaine, and this more expanded case, though they're both just theory. Amaya Moro-Martin tries to tie 'Omuamua to it here, but I'm not sure there's much uptake on that. WilyD 20:51, 11 July 2019 (UTC)

Exploration

The article mentions the Kepler mission, but will the James Webb Space Telescope be able to study the Oort cloud? Steinbach (talk) 09:59, 13 October 2018 (UTC)

Not. Ruslik_Zero 20:26, 11 February 2019 (UTC)

Stop changing "hypothetical" to "theoretical"

Someone seems to have a problem with the word "hypothetical" in this article. Maybe they don't know the difference between a hypothesis and a theory in science. So I'll explain.

A proposed idea that explains phenomena is first a hypothesis. A scientific hypothesis may be very sound and may be accepted by most of the scientific community as being likely true. Sometimes scientists have a "working hypothesis" that is generally accepted as true and scientists proceed with their work as though it is true, it just hasn't been rigorously tested or observed.

When a proposed idea/model has been well shown by imperial evidence and/or rigorous testing, it is then called a theory.

What differentiates a hypothesis from a theory is NOT how sound the idea is and it's NOT how accepted it is by the scientific community. What differentiates them is whether or not there is imperial evidence or rigorous testing.

The Oort cloud is so far out it has not yet been observed in any way. The model is very sound and is well accepted by the scientific community. It is taught in schools because there is an extremely high degree of confidence in the scientific commutity that the model is correct. But, it has not yet been observed, thus it is called a "hypothesis"

And of course the correct adjective for a hypothesis is "hypothetical"

I personally believe there IS an Oort cloud beyond a doubt. Hopefully soon it will be observed so they we can change the words used. Until then, please accept the scientific community calling this a hypothesis and please stop changing "hypothetical" to "theoretical" Hexakaidecanitarian (talk) 13:00, 19 September 2019 (UTC)

"emperical" Excuse the typo. Hexakaidecanitarian (talk) 13:08, 19 September 2019 (UTC)

Important note. Whether or not something simply exists is never called "theoretical."

For example, in 1846 astronomers were looking for a hypothetical 8th planet beyond Uranus. They finally observed it and it went from "hypothesis" to "fact" never being called "theory."

The same with the Oort cloud. It's existance is hypothetical and when it's finally observed it becomes fact, never theory.

We don't refer to the kypier belt as "theory" It simply exists. It's existance is a fact. Hexakaidecanitarian (talk) 13:32, 19 September 2019 (UTC)

The theoretical Oort cloud has been "Rigorously tested" via the observation of hundreds of Oort Cloud comets. -- Kheider (talk) 00:47, 27 September 2019 (UTC)

And really, the scientific community doesn't really call it a hypothesis anyways. "The Oort cloud is a population of small bodies, predominantly comets, found today at 1E4 ∼ 1E5 au from the Sun" "The outer region of the solar system is populated by a large number of planetesimals. Further away, more than 1000 AU from the Sun, and almost extending to the nearest stars, is the Oort cloud." "this distinction was made because the trans-Neptunian population is indeed observed on orbits lying beyond or close to Neptune, whereas the long-period comets coming from the Oort cloud are only observed when they are injected into the inner solar system, making them observable from Earth." - it's probably like evolution in that it's a theory (we have a theoretical understanding of why it exists and how it operates) and it's a fact (we observe it to exist). WilyD 13:24, 12 November 2019 (UTC)

No, the Oort cloud has not been observed. The Oort cloud is a hypothetical cloud proposed as the sourse for trans neptunian long term comets. Of course these long term comets have been observed. You confuse observing these long term comets with observing the Oort cloud. The Oort cloud is proposed as rhe sourse for these observed comets. The Oort cloud has not been observed. Hexakaidecanitarian (talk) 12:30, 18 October 2020 (UTC)

And yet Halle-Bopp is captioned here as "an archetypical" Oort Cloud object. Which might have pleased old Jan, except he died 3 years before H-B was discovered. 2A01:CB0C:CD:D800:881E:A6AF:CA0:836A (talk) 14:20, 1 April 2021 (UTC)

Acronyms

(Sorry if this isn't the right place.)

Is ‘ICO’ an acronym/initialism for an Oort cloud object, and if so, what exactly does it stand for?

It's from this template which links to this article as ‘Oort cloud objects (ICO/OCOs)’ — but I can't find any explanation of those acronyms, either within Wikipedia, or on the web.  (The only relevant link on the acronym's page is for Intermediate Circular Orbit, but that seems to describe geocentric orbits unrelated to the Oort cloud.)  My best guess is ‘Inner Cloud Objects/Outer Cloud Objects’, but I can't understand why those would omit the most important word…

— Gidds (talk) 13:55, 7 September 2020 (UTC)

For better or worse it is short for Inner Cloud Object and Outer Cloud Object. -- Kheider (talk) 17:31, 7 September 2020 (UTC)