Talk:Oort cloud
From Wikipedia, the free encyclopedia
| This is the talk page for discussing improvements to the Oort cloud article. This is not a forum for general discussion of the subject of the article. |
Article policies
|
| Find sources: Google (books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
| Archives: 1, 2, 3 |
 | Oort cloud is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Wikipedia community. Even so, if you can update or improve it, please do so. | ||||||||||||||||||||||||||||||
 | Oort cloud is part of the Solar System series, a featured topic. This is identified as among the best series of articles produced by the Wikipedia community. If you can update or improve it, please do so. | ||||||||||||||||||||||||||||||
 | This article appeared on Wikipedia's Main Page as Today's featured article on August 8, 2011. | ||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||
| This  level-4 vital article is rated FA-class on Wikipedia's content assessment scale.It is of interest to the following WikiProjects: | |||||||||||||||||||||||
| ||||||||||||||||||||||||
.jpg){kind=small}
 Archives |
| 1, 2, 3 |
Wikipedia needs to lock in "hypothetical."
Some well intentioned editor keeps changing "hypothetical" to "theoretical." Perhaps they think it makes it sound more serious? I don't know exactly what their faulty thinking is.
There is a reason the first section is correctly titled the "Hypothesis" and NOT the "Theory."
When someone developes a model that explains phenomena, that "model" is a "theory."
Example: Einstein's theory of relativity.
When someone proposes "objects exist" to explain phenomena, those "objects" are "hypothetical" until their existence is empirically verified, at which point they are "fact."
Example: an 8th planet was hypothetical until Uranus was discovered, now it's fact.
A model will always remain a "theory." It does not matter how much evidence substantiates it, it will forever be a "theory."
Something theoretical forever remains theoretical (scientific theory).
Something hypothetical becomes fact with enough empirical evidence.
The Oort cloud is a hypothetical object (cloud of many objects) that is proposed as a source of long term comets. Currently, there is absolutely NO empirical evidence that it exists. However, if we one day do get enough empirical evidence of its existence, it goes from being "hypothetical" to being a "fact," something which cannot happen with a "theory." Hexakaidecanitarian (talk) 08:22, 20 May 2021 (UTC)
Before someone replies that "we DO have empirical evidence, long term comets" I'll deal with that now.
Long term comets, "fact," we "know" they exist. Long term comets are NOT part of the Oort cloud. Oort proposed long term comets in the past WERE part of the cloud, but somehow got knocked out.
An analogy: let's imagine we're at the bottom if a hill and we periodically see apples roll down the hill to us. We cannot see the top of the hill. I propose there is an apple tree at the top of the hill that has lots of apples, and something causes the apples to fall from the tree. Everyone with me agrees that is probably the case. I have NO empirical evidence of my hypothetical apple tree on the hill. Even though it makes good sense. Even though we know apples roll down the hill. And in this case we know all apples come from trees. The source "tree in this hill" has no empirical evidence.
Empirical evidence of the tree requires seeing the tree, touching the tree, hearing the trees branches in the wind, etc.
BTW, in this case, it happens to be that a monkey keeps stealing an old lady's apples and rolls them down the hill. No tree on the hill.
Likewise with the Oort cloud. We know there are long term comets. But there is no empirical evidence of a source "cloud." An, unlike the Apple tree, we don't even know if comments come from clouds of comets as their "source." Hexakaidecanitarian (talk) 09:26, 20 May 2021 (UTC)
Edit: by 8th planet I mean Neptune. Excuse my brain flatulence. Hexakaidecanitarian (talk) 11:52, 20 May 2021 (UTC)
- It is "Theoretical" because astronomers have observed many comets coming directly from the Oort cloud (with inbound aphelia 10,000-70,000AU from the Sun). We know they came directly from the Oort cloud because we can calculate their barycentric orbits back into the past. (Heliocentric solutions at the same epoch will have even larger orbits because the solution will not include the gravity of Jupiter.) -- Kheider (talk) 14:58, 20 May 2021 (UTC)
@Kheider, "It is "Theoretical" because astronomers have observed many comets coming directly from the Oort cloud (with inbound aphelia 10,000-70,000AU from the Sun)." I mean no disrespect, but this sentence makes zero sense. Let's start with the second part,"astronomers have observed many comets coming directly from the Oort cloud (with inbound aphelia 10,000-70,000AU from the Sun). OK, they haven't observer the Oort cloud, so they haven't observed anything coming from it. Astronomers have observed long term comets with aphelia from 10,000-70,000AU. The existance of these long term comets is a fact.
The fact that these comets exist is why Oort proposed his hypothetical cloud. Oort proposed there is a cloud of planetesimals in that region, this hypothetical cloud is NOT the long term comets we have observed, such comets are proposed to have been kicked out of the Oort cloud at some distant past time. The Oort cloud has not been observed.
So, you're putting the cart before the horse. The factual, known existance of long term comets with aphelia 10,000-70,000AU from the barycenter is the reason Oort hypotisized a cloud of non-comets remaining out in that distant region that is the source of these known comets.
Now, lets look at the first part of this sentence, "It is "Theoretical" because"
This shows a basic lack of understanding of what differentiates a hypothesis from a scientific theory. A scientific theory is a "theory" from the moment it is conceived until the end of time. When a "theory" is put forth, it is a theory even when there is absolutely NO evidence to support it. And, later, when there is a mountain of evidence to support it, and everybody in the scientific community accepts it, it is then called a "theory" because a "theory" IS ALWAYS a "theory." A theory is a "model" that explains phenomena. It will forever be a "model" thus a "theory." A "hypothesis" is a testable, falsifiable idea. If someone once had a hypothesis that "elephants cannot swim" we simply test it. Observe elephants in water deeper than their height. We have observed this and the empirical evidence shows "elephants can swim = fact" thus falsifying the original hypothesis. Scientists collect empirical evidence (i.e. make observations) to either confirm a hypothesis (thus it becomes fact) or disprove it (falsify the hypothesis).
When the question at hand is simply whether or not an object exists, until it's existance is confirmed or disproven it is "hypothetical."
It doesn't matter if most of us consider it to be silly and unlikely (there is a giant space alien wandering way out there which occasionally poops out a mud ball towards the sun which freezes and becomes another long term comet) or serious and likely (there is a spherical cloud of planitessimals out there and occasionally something gets knocked out of the cloud and becomes a long term comet) both are called "hypothetical" until we observe just what is out there. Hexakaidecanitarian (talk) 10:05, 21 May 2021 (UTC)
- It is theoretical as it is a successful working scientific model that explains all comets with periods greater than ~100000 years. Objects in the Oort cloud are on unstable orbits that are not perfectly spherical. Everything orbiting the Sun has a best-fit orbital period even if that period is millions of years. -- Kheider (talk) 13:12, 21 May 2021 (UTC)
Hypothetical
Just to make a point, I just thought up the Hexa giant impact hypothesis (a modified version of the giant impact hypothesis).
More than 4.5 billion years ago there existed an icy planet with a mass several times the mass of the earth with an orbital distance from the sun of about 20 AU. Let's call it planet Comet.
A massive interstellar object collided with this planet breaking it up into large pieces and propelling those pieces into the solar system. The Comet debris then had an orbit with a perihelion of about 1 AU and an apheliin of about 20 AU.
About 4.5 billion years ago the Comet debris field encountered a pre-Earth planet, let's call it Terra1. A large piece about the size of Mars struck Terra1 resulting in the formation of the Earth and the Moon (the Earth getting its abundance of water from this large icy Comet fragment).
Most of the debris field which missed Tera1 was then scattered in various directions at this collision yet the individual pieces still had an apheliin of about 20 AU.
But of the piece which struck Tera1, much of it exploded away losing momentum to the collision, a large mass of this collision debris had an aphelion of about 10 AU.
Over the next 4.5 billion years, the Earth and moon formed and cooled. And the now 2 debris fields continued to break up. Over time, further collisions resulted in short period comet orbits.
Due to collisions, tidal forces of near passes to planets, regular effects from the sun at perihelion, etc. the larger pieces continued to break up until now what remains are scattered smaller fragments.
This is my just formed hypothesis. Planet Comet, hypothetical. Planet Terra1, hypothetical. It doesn't matter him much I work on this, it doesn't matter if it all makes sense. These "objects" shall forever be called "hypothetical" unless we go back in time and OBSERVE them, and upon observing they become "fact." At no point can these objects be called "theoretical." IT'S SIMPLY THE *WRONG* WORD TO USE.
PS. I kinda like my new hypothesis. Hexakaidecanitarian (talk) 11:30, 21 May 2021 (UTC)
Final fix on hypothetical/theoretical, hopefully.
Since you cannot refer to an objects possible existance as theoretical (unless its proposed existance is solely the prediction of a model, such as the Higgs Boson). You cannot refer to "the Oort cloud" meaning the cloud itself as "theoretical" but instead must refer to the object as "hypothetical." However, when there is a theoretical concept surrounding the object, you can use "theoretical" to the concepts concerning the object. NASA worded it as so: https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/
"Though long-period comets observed among the planets are thought to originate in the Oort Cloud, no object has been observed in the distant Oort Cloud itself, leaving it a theoretical concept for the time being. But it remains the most widely-accepted explanation for the origin of long-period comets."
Referring to the Oort cloud as a " theoretical concept" of a cloud is correct. Good job NASA.
To summarize: The entity "the Oort cloud" is "hypothetical." The concept "the Oort cloud" is "theoretical."
So let's finally agree on NASA's wording.
PS. Yes, this is pedantic. Hexakaidecanitarian (talk) 14:40, 21 May 2021 (UTC)
- Comets that spend most of their time in the Oort cloud are members of the Oort cloud. (2002 RP120 is a TransNeptunian Object even though it comes well inside of Jupiter.) We have seen numerous comets that spend most of their time in the Oort cloud. The closer an object is to the Sun the faster it needs to move to maintain the orbit. Objects move slowest when furthest from the Sun (aphelion) and fastest when closest to the Sun (perihelion) and this is why Oort cloud comets spend most of their time in the Oort cloud. (Equal areas are swept out in equal times at any location in the ellipse.) While in the Oort cloud these slow moving objects are subject to numerous small perturbations that can make the object unbound/bound. The Oort cloud is theoretical regardless of whether it is called a concept, idea, or a substantiated scientific model. -- Kheider (talk) 19:21, 21 May 2021 (UTC)
- Ahh, I see that @Kheider: has dug in their heels for many years about this terminology and will not be easily dislodged from owning the incorrect assertions of scientific theory here.
- This is sloppy science and unbecoming of a Wikipedia article which should be drawing more firm distinctions between "scientific theory" which is distinct from "hypothesis". Even Jan Oort himself correctly labeled his hypothesis as such.
- Unless you have WP:RS which support the assertion that this is a formal scientific theory which has undergone codification and attempts to falsify it, then you are contravening Wikipedia policy and performing original research. It is a failure of WP:Verifiability to claim that this is a theory when it's not. You can argue as much as you want but in the end, the sourcing and the scientists have the final say. 2600:8800:1E8F:BE00:1E8F:17D5:D7BB:C939 (talk) 20:42, 21 May 2025 (UTC)
- "Hypothesis", ca. 2006: https://pdf.danmalo.info/wp-content/uploads/2015/01/Oort-Cloud-Formation-and-Dynamics2.pdf
- 1986 paper. No mention of "Theory".
- 2021 paper. Hypotheses relating to Oort cloud.
- Hypothetical Oort Cloud. Article <11 years old.
- 1982 NASA Publication. "Oort's Hypothesis"
- ESA article. No reference to "theory".
- I am afraid that there is a consensus of scholars and scientists who regard this 75-year-old hypothesis as a hypothesis in 2025. There seems to be no such article that defines it as a theory or explains how it was advanced or proudly announces its promotion. I am afraid that Wikipedia cannot support unverifiable assertions, especially repeated ones which misrepresent verifiable facts found in reliable secondary and primary sources. This is inexcusable in a scientific article to deliberately and wilfully misunderstand the differences between theory, hypothesis, and the meanings of words such as "postulate" and "propose" and "think"! 2600:8800:1E8F:BE00:23BA:E2E6:8269:3B50 (talk) 20:35, 23 May 2025 (UTC)
- Modern sources, including the ones you cite above, do not use "theoretical" or "hypothetical" and that is how our intro should be. The word "theoretical" should be removed. The word ""hypothetical" should not replace it because modern sources just discuss "the Oort cloud". The word "Hypothesis" should be used in the discussion of history according to cited sources. Eg the source says "Jan Hendrik Oort hypothesized the existence of a distant cloud of cometary objects ..." and his work should thus be characterized as forming a hypothesis.
- We don't describe black holes or active galactic nucleus as theoretical or hypothetical. Similarly there is no need for a qualification here. Johnjbarton (talk) 04:04, 24 May 2025 (UTC)
- You seem to only edit religious articles. -- Kheider (talk) 19:45, 22 May 2025 (UTC)
- I have have restored your talk page vandalism 2600:8800:1E8F:BE00:23BA:E2E6:8269:3B50. Please read WP:Single-purpose account/WP:Talk page guidelines#Editing others' comments. -- Kheider (talk) 14:22, 24 May 2025 (UTC)
- In 1950 the Oort Cloud was a hypothesis as before then most Oort cloud comets where simply *assumed* to have an eccentricity=1 as the technology not there to have confident in the difference between e≈1 and a truly strong eccentricity notably above 1 that would suggest an object did not come from the Oort Cloud. We now have a well tested Scientific theory that fits all comet discoveries. We have only discovered two Interstellar objects that have strong enough eccentricities to show they are not from the Solar System. The rest of the objects come from the planetary region, Kuiper belt, or Oort Cloud. -- Kheider (talk) 14:22, 24 May 2025 (UTC)
- Fine, wonderful even. But the introductory paragraph for the article on the Oort cloud should refer to the topic in the same way as used in reliable mainstream secondary references. These references to not include the word "theoretical" or "hypothetical". Johnjbarton (talk) 16:06, 24 May 2025 (UTC)
- Actually I see the words "theoretical" and "hypothesis" in various forms in many articles, including some listed above. Most do not attempt to distinguish between the concepts. This article seems notable:
- "What is the Oort Cloud?"
- My opinion is, it's above the pay grade of Wiki editors to decide which term is best. But I do not agree with John that both terms should be omitted, because that makes it sound like settled science. It may be weaselly, but how about using both terms? "... is a theorized hypothetical vast cloud..." ? Assambrew (talk) 17:16, 24 May 2025 (UTC)
- Based on my reading, the Oort cloud is settled science. Can you provide any (modern) source that expresses doubts or alternatives to the Oort cloud? Johnjbarton (talk) 17:28, 24 May 2025 (UTC)
- The article I cited above has, "Although it has not yet been proven through direct observation, the existence of the Oort Cloud is widely accepted in the scientific community." Widely accepted is not quite the same as settled. Assambrew (talk) 17:48, 24 May 2025 (UTC)
- As for alternatives, it's now known that at least some comets originate from interstellar space. I can imagine that many or most long period comets originate from there, and only become bound upon the close encounter with the solar system. But again, that's physics above my pay grade :-) Assambrew (talk) 18:01, 24 May 2025 (UTC)
- Ok, "widely accepted" works for me. In my opinion, "hypothetical" or "theoretical" does not belong in the first sentence precisely because of the kind of long winded discussion going on here. A non-technical, non-scientifically oriented reader will take these terms to mean "made up by some bloke". These terms generally do not mean "widely accepted" among average readers.
- In fact we could start with
- The Oort cloud (pronounced /ɔːrt/ AWT or /ʊərt/ OORT), sometimes called the Öpik–Oort cloud, a region of the outer Solar System, is the source of most comets.
- Johnjbarton (talk) 22:27, 24 May 2025 (UTC)
- Again, phrasing the lead sentence without any reference to hypothetical or theoretical leaves the impression that the existence of the Oort cloud is settled science, which it is not. You like "widely accepted", okay how about "... a hypothetical region of the outer Solar System that is widely accepted by the scientific community to be the source of most comets.". Assambrew (talk) 23:01, 24 May 2025 (UTC)
- Not settled science. There are two things going on here. The Oort Cloud is both the name given to the outer region of the solar system and the structure of that region. We know the outer solar system is there. The structure remains hypothetical. The definition in the glossary of the International Astrophysical Union starts
The Oort Cloud is a hypothetical region of the outer Solar System ...
. A 2021 paper saysThe Oort cloud is the source of long-period comets but has not been observed directly, and its origins remain theoretical.
StarryGrandma (talk) 18:46, 24 May 2025 (UTC)- We know the Oort Cloud is spherical as comets come from the Oort Cloud in all different directions on local/near parabolic orbits. We can not directly observed comets 100-km-in-diameter that are currently 2,000+ AU from the Sun because they are simply too faint. But we can observe comets when they are inside the orbit of Neptune and determine roughly where they originate from and that they took a million years or more to get to the planetary region. This Scientific theory has passed every observation made. The fact we have only observed two interstellar comets only strengthens the existence of the Oort Cloud. -- Kheider (talk) 19:42, 24 May 2025 (UTC)
- Determining structure and composition is more complicated than that. The inner part of the cloud is believed to be doughnut-shaped. Still hypothetical. StarryGrandma (talk) 21:00, 24 May 2025 (UTC)
- We do not "know the Oort cloud is spherical" because we do not know that it actually exists. It is a hypothesis that is widely accepted, but hasn't been proven. The IAU calling it hypothetical should be the clincher. Assambrew (talk) 23:09, 24 May 2025 (UTC)
- I agree the IAU glossary is an important source, but please read the source. It's not an official document but rather a "definition have been approved by a research astronomer and a teacher." Johnjbarton (talk) 23:43, 24 May 2025 (UTC)
- What's wrong with the source? Sounds like a research astronomer to ensure accuracy, and a teacher to ensure understandable language. Assambrew (talk) 00:00, 25 May 2025 (UTC)
- I am only pointing out that this source is not "The IAU calling it hypothetical". I think it is a fine source, one of many. Johnjbarton (talk) 00:46, 25 May 2025 (UTC)
- What's wrong with the source? Sounds like a research astronomer to ensure accuracy, and a teacher to ensure understandable language. Assambrew (talk) 00:00, 25 May 2025 (UTC)
- I agree the IAU glossary is an important source, but please read the source. It's not an official document but rather a "definition have been approved by a research astronomer and a teacher." Johnjbarton (talk) 23:43, 24 May 2025 (UTC)
- The issue is not the origin, structure, or composition, all of which could be described as hypothetical or theoretical depending on the source. The question is the opening sentence characterizing the subject broadly and simply. So the 2021 paper you point to supports calling this simply the Oort cloud, and discussing the origin via theories. This is how I see the topic covered in multiple sources. Johnjbarton (talk) 22:19, 24 May 2025 (UTC)
- We know the Oort Cloud is spherical as comets come from the Oort Cloud in all different directions on local/near parabolic orbits. We can not directly observed comets 100-km-in-diameter that are currently 2,000+ AU from the Sun because they are simply too faint. But we can observe comets when they are inside the orbit of Neptune and determine roughly where they originate from and that they took a million years or more to get to the planetary region. This Scientific theory has passed every observation made. The fact we have only observed two interstellar comets only strengthens the existence of the Oort Cloud. -- Kheider (talk) 19:42, 24 May 2025 (UTC)
- The article I cited above has, "Although it has not yet been proven through direct observation, the existence of the Oort Cloud is widely accepted in the scientific community." Widely accepted is not quite the same as settled. Assambrew (talk) 17:48, 24 May 2025 (UTC)
- Based on my reading, the Oort cloud is settled science. Can you provide any (modern) source that expresses doubts or alternatives to the Oort cloud? Johnjbarton (talk) 17:28, 24 May 2025 (UTC)
- Fine, wonderful even. But the introductory paragraph for the article on the Oort cloud should refer to the topic in the same way as used in reliable mainstream secondary references. These references to not include the word "theoretical" or "hypothetical". Johnjbarton (talk) 16:06, 24 May 2025 (UTC)
- In 1950 the Oort Cloud was a hypothesis as before then most Oort cloud comets where simply *assumed* to have an eccentricity=1 as the technology not there to have confident in the difference between e≈1 and a truly strong eccentricity notably above 1 that would suggest an object did not come from the Oort Cloud. We now have a well tested Scientific theory that fits all comet discoveries. We have only discovered two Interstellar objects that have strong enough eccentricities to show they are not from the Solar System. The rest of the objects come from the planetary region, Kuiper belt, or Oort Cloud. -- Kheider (talk) 14:22, 24 May 2025 (UTC)
Astronomers and astrophysicists know that the Oort Cloud is something we are assuming. We don't say that in every article written about it. I have several references that say it is an hypothesis.[1][2][3] We cannot rely on articles that don't mention it. To counter that we need a source that says it has been comfirmed. I can't find one. Instead I find: Interestingly, scientists have not yet confirmed the Oort Cloud's existence because the icy objects that it is thought to contain are small and so far away that they can't be seen.
[4]
- StarryGrandma (talk) 16:42, 27 May 2025 (UTC)
- Ok I buy that argument. Hypothetical Johnjbarton (talk) 16:50, 27 May 2025 (UTC)
- We have observe comets from the Oort Cloud every year. It is a working scientific theory. -- Kheider (talk) 17:07, 27 May 2025 (UTC)
- Sure, and, in that theory the Oort cloud is the key hypothesis. The hypothesis of the Oort cloud is the basis for the theory that explains certain kinds of comets. Johnjbarton (talk) 18:16, 27 May 2025 (UTC)
- To change the lead of a theory that has being working for decades is to harm this article. Planet Nine is what you would call hypothetical. Every comet discovered supports the Oort Cloud theory. Not every Extreme trans-Neptunian object supports the hypothetical Planet Nine. -- Kheider (talk) 14:00, 30 May 2025 (UTC)
- Sure, and, in that theory the Oort cloud is the key hypothesis. The hypothesis of the Oort cloud is the basis for the theory that explains certain kinds of comets. Johnjbarton (talk) 18:16, 27 May 2025 (UTC)
- We have observe comets from the Oort Cloud every year. It is a working scientific theory. -- Kheider (talk) 17:07, 27 May 2025 (UTC)
References
- "Glossary Term: Oort Cloud". IAU Office of Astronomy for Education. Retrieved May 26, 2025.
- Delsemme, Armand H. (May 10, 2025). "Oort cloud". Encyclopedia Britannica.
- Trefil, James (August 24, 2001). The Encyclopedia of Science and Technology. Routledge. p. 361. ISBN 978-1-136-75362-6.
- Starkey, Natalie (March 8, 2018). Catching Stardust: Comets, Asteroids and the Birth of the Solar System. Bloomsbury Publishing. p. 45. ISBN 978-1-4729-4403-0.
This whole article
Most of the language in this article assumes the Oort cloud exists. Grassynoel (talk) 09:52, 13 January 2023 (UTC)
Relative distances
The graphic in "Stellar perturbations and stellar companion hypotheses" has some wrong locations
The graphic in the "Stellar perturbations and stellar companion hypotheses" section has multiple factual errors, as mentioned in its talk page. Template:Solar_encounters has correct figures for at least the two mentioned in the talk page comment, though I haven't checked others.
I just removed it in hopes that someone can maybe either re-create the graphic or get the original author to fix the issues and re-add it. impinball (talk) 18:49, 19 February 2023 (UTC)
Corrected small misstake
I changed it from "Fastest probe" to "Once fastest probe" the parker solar probe currently is faster. 2A00:801:700:8A66:F66D:1459:EC6C:31A1 (talk) 16:52, 16 April 2024 (UTC)
- @2A00:801:700:8A66:F66D:1459:EC6C:31A1 Dont mind if I did misstake, I am new to Wikipedia but I ain't stupid. 2A00:801:700:8A66:F66D:1459:EC6C:31A1 (talk) 16:55, 16 April 2024 (UTC)
- @2A00:801:700:8A66:F66D:1459:EC6C:31A1 Yup fixed FalseWorldDictionary (talk) 17:26, 16 April 2024 (UTC)
Small fact correction
I have once again changed a small thing in the article. Voyager 1 is not the fastest probe, therfor it was changed to "once fastest". This is a usefull correction as it can be missleading to read it is the fastest. Signed FalseWorldDictionary. FalseWorldDictionary (talk) 15:13, 28 June 2024 (UTC)
"easily affected by the gravitational pulls of both passing stars and the Milky Way itself"
This part should also include a gravitational component by the cloud itself. When gravity from the nearby star system is really low (net value), the cloud itself is equally so a gravitationally active or rather significant factor. It keeps itself intact mostly by microgravity. Consider a density of colloidal matter in the range of 1E-15 to 1E-18 grams per cubic meter, a density not uncommon for the Oort cloud, and you find that at a range of approximately 0.5LY distance from the Sun the microgravity is enough to counter the inward pull towards the Sun by such a degree to prevent 'rapid' acceleration towards the Sun. WIth rapid, the term is loose, the acceleration is small enough to never having accelerated to anywhere near enough speed to become part of the Sun's system. That's why it's still there. Large gravity sources like stars appear the greater attracting force, and yet the colloidal matter's grravity output exceeds that of all regular such large objects by a factor of 3-4. It's why they assume the dark matter, but it's not dark matter. It's merely colloidal, and in vast volumes, combining into great gravity sources. It's ike putting the mass of a star in collloidal form into a sphere of 1.5 LY radius. You can't see it, yet it's there, and despite the colloidal form, it still generates the same amount of gravity.
I'll change the line to reflect this by adding "and the cloud's own gravity"
— Preceding unsigned comment added by 62.45.38.40 (talk • contribs) 07:26, 21 March 2025 (UTC)
- Please do not remove signature lines Johnjbarton (talk) 16:01, 24 May 2025 (UTC)
New paper on structure
The following paper appeared in April and it has an especially clear introduction to Oort cloud structure.
- Nesvorný, David; Dones, Luke; Vokrouhlický, David; Levison, Hal F.; Beaugé, Cristian; Faherty, Jacqueline; Emmart, Carter; Parker, Jon P. (April 2025). "A Spiral Structure in the Inner Oort Cloud". The Astrophysical Journal. 983 (1): 74. doi:10.3847/1538-4357/adbf9b. ISSN 0004-637X.
{{cite journal}}: CS1 maint: unflagged free DOI (link)
While the new results in the paper have not been cited by other publications as yet, the introduction can be used as a secondary ref. Johnjbarton (talk) 15:21, 25 May 2025 (UTC)
Dud reference
@Themeparks: on 23 March 2025 you added a reference titled "Fading of long-period comets in near-parabolic orbits". However there appears to be no such article with that title or DOI like this. Please check what reference you intended to insert here. Graeme Bartlett (talk) 12:31, 23 June 2025 (UTC)