Oort Cloud - Agreed terms help sensible discussion.

Catastrophe

The devil is in the detail
Oxford Dictionary of Astronomy Ian Ridpath Oxford University Press 2011
"A roughly spherical halo of comet nuclei surrounding the Sun, out to perhaps 100,000 AU (over one third of the distance to the nearest star). Its existence was proposed in 1950 by J H Oort to account for the fact that new comets approach the Sun on highly elliptical orbits at all inclinations."
"The Oort Cloud remains a theoretical concept, since we cannot currently detect comets at such great distances. The cloud is estimated to contain 10^12 comets remaining from the formation of the Solar System. The most distant members are fairly loosely bound by the Sun's gravity. There may be a greater concentration of comets relatively close to the ecliptic, at 10,000 to 20,000 AU from the Sun, extending inwards to join the Kuiper Belt. Oort Cloud comets are affected by the gravitational influence of passing stars, occasionally being perturbed into orbits which take them through the inner Solar System."

View: https://imgur.com/a/1DJboMw

Don't forget comets do not develop a tail until near the Sun, so are otherwise not easily visible, especially at great distances. Comet Tempel 1 NASA.

Complete History of the Universe All About Space 2016

"Oort Cloud
An enormous region of space encapsulating the planets and stretching 50,000 AU from the Sun to around 100,000 AU in diameter at its outer boundaries: from one side to the other its about 2 light years long."
"It's made of water, ammonia and methane ice, in the form of icy particles and trillions of larger bodies. It's suspected that many of the Solar System's comets were born here, and some trans-Neptunian objects are Oort Cloud members too. It's divided into two distinct regions, the inner and outer Oort Cloud containing several trillion comets larger than 1 km (0.62 mile) in diameter. [These must be estimates, since they cannot be seen at this distance] Considering the size of the Oort Cloud, it would take our fastest spacecraft launch, New Horizons, around 20,000 years to reach its outer edge at 58,536 km/hour (36.373 miles/hour. The Oort Cloud isn't very massive, just a fraction pf the 100 or so Earth masses of material ejected from the centre of the Solar System."

Collins Discovery Guide - Universe Pam Spence William Collins 2018

"The most spectacular objects in the Solar System are the comets, which can produce awe inspiring tails millions of km long. Cometary orbits are not confined to the plane of the Solar System, where the planets and asteroids are found, but can approach the Sun from any angle. This fact, together with the numbers of new comets observed each year, suggests that there is a reservoir of cometary material surrounding the Solar System. This reservoir is called the Oort Cloud which is believed to extend from around 30,000 to 100,000 AU."
"The Oort Cloud has never actually been observed - its existence was suggested by the Dutch astronomer J H Oort to explain the trajectories and number of long period comets (comets that take 200 years or more to orbit the Sun) that are seen. However, comets have been seen coming directly from that far out and it is the logical explanation for their origin.


View: https://imgur.com/a/neeV7vm

"The Oort Cloud is a theoretical spherical cloud of predominantly icy planetesimals that is believed to surround the sun at a distance of up to around 100,000 AU (2 ly). This places it in interstellar space, beyond the sun's Heliosphere where it defines the cosmological boundary between the solar system and the region of the sun's gravitational dominance."

So one suggestion is that the Oort Cloud is a hypothetical subdivision of interstellar space; nonetheless, inhabited by large numbers of comets - which can be diverted towards the inner Solar System - and possibly other objects.
The dust and (frozen) water are natural inhabitants of such an environment.








WORK IN PROGRESS last edit Monday 12th July 18.20 BST.
 
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NASA on Oort Cloud article that puts the inner region perhaps as close as 2000 AU, but suggests the outer region could extend to the 100,000 AU (~ 1.4 lyr). [I had recall reading it was ~ 60,000 AU max. but perhaps it has grown as science has advanced.]

The Oort Cloud hypothesis, no doubt, was developed once an understanding of how planets actively toss smaller objects outward. The smaller the object, the farther it can be tossed.

But why is it held that objects kicked-outward should be beyond 2000 AU? I've seen home-run batters hit the ball only a few feet, so what am I missing?

Also, there is no model that can explain what happened in the dynamic phase of planetary migrations since an accurate explanation must explain what we see today. A few models, admittedly, seem to do a great job for most of the planets.
 

Catastrophe

The devil is in the detail
NASA on Oort Cloud article that puts the inner region perhaps as close as 2000 AU, but suggests the outer region could extend to the 100,000 AU (~ 1.4 lyr). [I had recall reading it was ~ 60,000 AU max. but perhaps it has grown as science has advanced.]

The Oort Cloud hypothesis, no doubt, was developed once an understanding of how planets actively toss smaller objects outward. The smaller the object, the farther it can be tossed.

But why is it held that objects kicked-outward should be beyond 2000 AU? I've seen home-run batters hit the ball only a few feet, so what am I missing?

Also, there is no model that can explain what happened in the dynamic phase of planetary migrations since an accurate explanation must explain what we see today. A few models, admittedly, seem to do a great job for most of the planets.
Helio, thank you for your (as always) excellent comments. I have not completed this subject yet but, I believe, it is already apparent that very little is known for certain about this proposed model. In the final analysis, it may turn out as "there are comets in them there clouds". Cat :) :) :)
 
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In the final analysis, it may turn out as "there are comets in them there clouds". Cat :) :) :)
:) Yes. I wonder what the latest count is on comets from the Oort. It may only be several? We need data.:)

Also, one possible reason for the 2000 AU minimum might be that they would fall back toward the Sun with a free-fall time of only 90k years. So, it may be that those comets closer would have already been fried after millions of years of passes. Even those with a large perihelion, but inside, say, Neptune, would have likely had orbital changes that would eventually have caused their demise. But I'm only guessing.
 
Hi everyone, if I'm not mistaken (I literally can't) this subject was first introduced by me in a forum not a lot time ago. I see this is a different section, for this reason I'm not used to it (I discovered this new section today since I log in with my phone, when I used the computer this region isn't marked and I can't see it). Someone can explain me please what kind of difference there is between "forum list" and "trending"?
Anyway, while I beg your pardon for these questions, I want to add something that isn't present here: between the Oort Cloud and the Kuiper Belt there is a region of space known as "scattered disk". This region is a part of our solar system, whose extent lay from 55 A.U. away from the Sun to more than 100 A.U., is very cold and very far from us. This is made by the leftovers of the formation of our solar system as well as the Oort Cloud. It might have been defined by you as the inner part of the Oort Cloud, and this isn't wrong at all since there isn't a real distinction.
Comets of the short period (comets who complete the cycle around the Sun within 200 years) aren't tilted in comparison to the plan of the solar system and may reach this region; Comets of the long period (comets who complete the cycle around the Sun in more than 200 years) have a certain slope with the plan and reach this region called Oort Cloud.
 

Catastrophe

The devil is in the detail
Helio, not being American, I don't know what a baseball looks like. I assume that it is rounded, so I was looking for the next in the series (ignoring colour).
You are correct - distance apart is not scalar.

Cat :) ;) :)
 

Catastrophe

The devil is in the detail
I almost used a Nolan Ryan analogy in another thread, but did I introduce a baseball one here?

Yes, baseballs are round, and footballs are elongated. *wink* [I was rooting for England, btw.]
You cannot turn on a tv here without still hearing about it interminably!
BTW, I see you know that footballs (soccer) are round and rugby balls are elongated (ellipsoid). Cat :)
 
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Catastrophe

The devil is in the detail
"The baseball analogy is a basic explanation of orbital properties." #12

Not a clue. Nor about Nolan Ryan.
However, a cousin of my father did play cricket for Surrey and England - long, long ago.
How anyone can play a ball game with a round bat, I cannot imagine. Cricket bats have a flat front but a triangular back/

Cat :)

;) ;) ;) P.S. Have added to Oort Cloud above. I believe it is supposed to be English Football shaped, rather than any alternative.
 

Catastrophe

The devil is in the detail
THREAD Re-STARTED HERE and consolidated.

Oxford Dictionary of Astronomy Ian Ridpath Oxford University Press 2011

"A roughly spherical halo of comet nuclei surrounding the Sun, out to perhaps 100,000 AU (over one third of the distance to the nearest star). Its existence was proposed in 1950 by J H Oort to account for the fact that new comets approach the Sun on highly elliptical orbits at all inclinations."
"The Oort Cloud remains a theoretical concept, since we cannot currently detect comets at such great distances. The cloud is estimated to contain 10^12 comets remaining from the formation of the Solar System. The most distant members are fairly loosely bound by the Sun's gravity. There may be a greater concentration of comets relatively close to the ecliptic, at 10,000 to 20,000 AU from the Sun, extending inwards to join the Kuiper Belt. Oort Cloud comets are affected by the gravitational influence of passing stars, occasionally being perturbed into orbits which take them through the inner Solar System."


View: https://imgur.com/a/1DJboMw

Don't forget comets do not develop a tail until near the Sun, so are otherwise not easily visible, especially at great distances. Comet Tempel 1 NASA.

Asteroids, Meteorites and Comets Linda T Elkins-Tanton Chelsea House 2006

"Long period comets have traditionally been thought to come from a gigantic, diffuse cloud, about 30,000 to 100,000 AU from the Earth. This region is called the Oort Cloud, after the astronomer Jan Oort, who first demonstrated its existence. It is thought that most of these comets originated near Uranus and Neptune. Oort suggested that there are about 100 billion comets in the Oort Cloud. Comets are thought to be perturbed out of the Oort Cloud by a number of processes, including passing stars. It is thought that the heavy, early cratering on Jupiter's and Saturn's satellites was caused by Oort Cloud bodies. Some scientists also think that the Earth's water budget came from these bodies."


Complete History of the Universe All About Space 2016

"Oort Cloud
An enormous region of space encapsulating the planets and stretching 50,000 AU from the Sun to around 100,000 AU in diameter at its outer boundaries: from one side to the other its about 2 light years long."
"It's made of water, ammonia and methane ice, in the form of icy particles and trillions of larger bodies. It's suspected that many of the Solar System's comets were born here, and some trans-Neptunian objects are Oort Cloud members too. It's divided into two distinct regions, the inner and outer Oort Cloud containing several trillion comets larger than 1 km (0.62 mile) in diameter. [These must be estimates, since they cannot be seen at this distance] Considering the size of the Oort Cloud, it would take our fastest spacecraft launch, New Horizons, around 20,000 years to reach its outer edge at 58,536 km/hour (36.373 miles/hour. The Oort Cloud isn't very massive, just a fraction pf the 100 or so Earth masses of material ejected from the centre of the Solar System."

Collins Discovery Guide - Universe Pam Spence William Collins 2018

"The most spectacular objects in the Solar System are the comets, which can produce awe inspiring tails millions of km long. Cometary orbits are not confined to the plane of the Solar System, where the planets and asteroids are found, but can approach the Sun from any angle. This fact, together with the numbers of new comets observed each year, suggests that there is a reservoir of cometary material surrounding the Solar System. This reservoir is called the Oort Cloud which is believed to extend from around 30,000 to 100,000 AU."
"The Oort Cloud has never actually been observed - its existence was suggested by the Dutch astronomer J H Oort to explain the trajectories and number of long period comets (comets that take 200 years or more to orbit the Sun) that are seen. However, comets have been seen coming directly from that far out and it is the logical explanation for their origin.


What is the Oort Cloud?
For thousands of years, astronomers have watched comets travel close to Earth and light up the night sky. In time, these observations led to a number of paradoxes. For instance, where were these comets all coming from? And if their surface material vaporizes as they approach the sun (thus...
phys.org




View: https://imgur.com/a/neeV7vm

"The Oort Cloud is a theoretical spherical cloud of predominantly icy planetesimals that is believed to surround the sun at a distance of up to around 100,000 AU (2 ly). This places it in interstellar space, beyond the sun's Heliosphere where it defines the cosmological boundary between the solar system and the region of the sun's gravitational dominance."

So one suggestion is that the Oort Cloud is a hypothetical subdivision of interstellar space; nonetheless, inhabited by large numbers of comets - which can be diverted towards the inner Solar System - and possibly other objects.
The dust and (frozen) water are natural inhabitants of such an environment.







WORK IN PROGRESS last edit Monday 12th July 18.20 BST.
 
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Excuse me for this question, but it's something I really can't figure out (and I can't search):
How can I see the stars if the Oort Cloud exist? I mean, how possible is watching them if we have a shield of rocks half-way?
 

Catastrophe

The devil is in the detail
If you imagine a point at the centre of the Earth, and then imagine a cube of one metre, then the size of the Earth. Think how much space there is in the Earth compared with the metre cubed. Now imagine how many people there are on the surface of the planet. If you were able to stand at the centre of the Earth and look out, how could you imagine being to see beyond all those people.? How could there be any space between them to see through?

Now imagine the size of the Oort Cloud.

Cat :)
 
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Excuse me for this question, but it's something I really can't figure out (and I can't search):
How can I see the stars if the Oort Cloud exist? I mean, how possible is watching them if we have a shield of rocks half-way?
The vastness of volume in the Oort is such that a even a super Earth would be less than the size of a drop of water sized to the entire Pacific ocean.
 
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If you imagine a point at the centre of the Earth, and then imagine a cube of one metre, then the size of the Earth. Think how much space there is in the Earth compared with the metre cubed. Now imagine how many people there are on the surface of the planet. If you were able to stand at the centre of the Earth and look out, how could you imagine being to see beyond all those people.? How could there be any space between them to see through?

Now imagine the size of the Oort Cloud.

Cat :)
Maybe I understand: between that rocks there is space(?). So, holes allow light to get through!
The vastness of volume in the Oort is such that a even a super Earth would be less than the size of a drop of water sized to the entire Pacific ocean.
True! Thank you!
 
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Maybe I understand: between that rocks there is space(?). So, holes allow light to get through!

True! Thank you!
The brief blocking of starlight is very useful to astronomy for determining things like the size of small objects closer to us.

However, take say a 100 meter dia. object midway in the Oor Cloud. It's angular size would be very close to 10,000 times smaller in angular diameter if it crossed in front of solar-sized star that is located 100 lyrs. away. Thus it would very hard to notice, no doubt.
 

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