Talk:Oort cloud

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

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 AU's 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)

Minor planets → objects[edit]

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. Serendipodous 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?[edit]

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. Serendipodous 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)

Inconsistency in sentence[edit]

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. Serendipodous 14:36, 9 October 2013 (UTC)

Moved from article[edit]

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)

"Nearly all isotropic"[edit]

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[edit]

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. Serendipodous 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)