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Thread: Oort Cloud Query

  1. #1 Oort Cloud Query 
    Forum Radioactive Isotope skeptic's Avatar
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    A simple question.

    I was reading about the Oort Cloud. I know that little is known about it, except that it is where the comets come from. Long period comets fall from all directions, which shows that the Oort Cloud is not restricted to the ecliptic. My reading said that it extended from about 1,000 astronomical units to about 100,000, which is a quarter of the way to alpha Centauri.

    Now, all this implies the plantetisimals in the Oort Cloud are orbiting our sun (though in million year orbits) but not in the ecliptic particularly. It appears to me to be more logical to assume that there is no Oort Cloud at all, but just a whole bunch of planetisimals randomely distributed through the galaxy, and orbiting the centre of the galaxy rather than our sun. As the sun moves, it will approach planetisimals, some of which will fall as comets.

    I am not an expert in this field, and I know that the scientific consensus is that the Oort Cloud exists. So my 'logic' is clearly wrong. But I would like to know what evidence there is to show that the oort Cloud is, in fact, restricted to a zone up to 100,000 AU's out and not further. Since the ecliptic is not involved, it appears the planetisimals were not part of the primordial cloud that formed the solar system. Which leads me to ask where they originated.

    One last question. Do we have evidence, such as infra red telescope evidence, to show if there is a greater concentration of dust and gas in the Oort Cloud, in addition to all those planetisimals?


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  3. #2  
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    From Wikipedia:
    -------------------------------------------------

    Astronomers conjecture that the matter composing the Oort cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the Solar System's evolution.[3] Although no confirmed direct observations of the Oort cloud are made, it may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well.[5] 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. These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System.[3] 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.[3][5]
    -----------------------------------------

    This seems somewhat similar to your conjecture.


    Last edited by mathman; July 1st, 2014 at 03:47 PM. Reason: typo
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  4. #3  
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    Thanks, mathman, but it does not quite answer my query.

    Why do astronomers believe the planetisimals in the Oort Cloud are part (albeit a distant part) of the solar system, and not just scattered through the galaxy?
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    Quote Originally Posted by skeptic View Post
    Thanks, mathman, but it does not quite answer my query.

    Why do astronomers believe the planetisimals in the Oort Cloud are part (albeit a distant part) of the solar system, and not just scattered through the galaxy?
    Maybe because it revolves around our sun? maybe because our sun's gravity affects it? maybe they are scattered around the galaxy but always connected with other solar systems as well... Just spit ballin' here.
    "Should any political party attempt to abolish social security, unemployment insurance and eliminate labor laws and farm programs, you would not hear of that party again in our political history. There is a tiny splinter group, of course, that believes that you can do these things. Among them are a few Texas oil millionaires, and an occasional politician or businessman from other areas. Their number is negligible and they are stupid."
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  6. #5  
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    Grumpy
    We cannot directly detect the Oort Cloud, or make measurements. Its presence is deduced from the movement of comets. The astronomer's understanding of its nature must somehow derive from comets.
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    not ADM!N grmpysmrf's Avatar
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    Quote Originally Posted by skeptic View Post
    Grumpy
    We cannot directly detect the Oort Cloud, or make measurements. Its presence is deduced from the movement of comets. The astronomer's understanding of its nature must somehow derive from comets.
    My spitballs never stick.
    "Should any political party attempt to abolish social security, unemployment insurance and eliminate labor laws and farm programs, you would not hear of that party again in our political history. There is a tiny splinter group, of course, that believes that you can do these things. Among them are a few Texas oil millionaires, and an occasional politician or businessman from other areas. Their number is negligible and they are stupid."
    President Dwight Eisenhower
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  8. #7  
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    Presumably they are thought to have formed from the same molecular cloud that formed the solar system. I don't think they formed in situ, but were kicked out to their current location. Probably formed much closer to the Sun.

    Secondly, it would be difficult to imagine a process that creates so many such objects in interstellar space (I'm not an astronomer, so maybe this is why I can't imagine it).
    Last edited by Zwirko; July 2nd, 2014 at 05:22 AM.
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    Quote Originally Posted by Zwirko View Post

    Secondly, it would be difficult to imagine a process that creates so many such objects in interstellar space (I'm not an astronomer, so maybe this is why I can't imagine it).
    In your attempts to understand this, it may be worth while to ponder on the time involved. The galaxy has been there for many billions of years, and no doubt there has been millions of novas and supernovas, plus all kinds of condensations of gas and dust clouds into suns and planets. Perhaps, somewhere in all that time, there may have also been sufficient time for planetisimal formation. By which I am admitting I do not know, either.
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    Quote Originally Posted by skeptic View Post
    A simple question.

    ...

    Now, all this implies the plantetisimals in the Oort Cloud are orbiting our sun (though in million year orbits) but not in the ecliptic particularly. It appears to me to be more logical to assume that there is no Oort Cloud at all, but just a whole bunch of planetisimals randomely distributed through the galaxy, and orbiting the centre of the galaxy rather than our sun. As the sun moves, it will approach planetisimals, some of which will fall as comets. ....
    Do they orbit the Sun?
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  11. #10  
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    I am not an expert in this field, and I know that the scientific consensus is that the Oort Cloud exists. So my 'logic' is clearly wrong. But I would like to know what evidence there is to show that the oort Cloud is, in fact, restricted to a zone up to 100,000 AU's out and not further. Since the ecliptic is not involved, it appears the planetisimals were not part of the primordial cloud that formed the solar system. Which leads me to ask where they originated.
    These is a grain of truth in your guess. It is proven that some comets don't originate from our solar system. These comets come to our solar system and then fly away, i.e. they don't have closed elliptic trajectories. While it is also obvious that comets will concentrate around stars.
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    Blas
    Do you thInk that planetisimals may be 'stolen' by the sun's gravity and pulled into solar orbit as it moves through the galaxy? I mean, in addition to pulling some into cometary orbits.
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    Quote Originally Posted by skeptic View Post
    Blas
    Do you thInk that planetisimals may be 'stolen' by the sun's gravity and pulled into solar orbit as it moves through the galaxy? I mean, in addition to pulling some into cometary orbits.
    I don't really understand what are you asking. Most of objects in Oort cloud originate from our Solar System. That is objects there formed together with our Sun. Sometimes stars come close to one another. It is very well possible that in such encounters Oort clouds of these two stars interchange some material.

    Objects of Oort cloud may change trajectories. These happens due to variety of reasons:
    1) Interaction with inner planets.
    2) Gravitational assists from each other.
    3) Interaction with other stars. Say famous Barnard's star (Barnard's Star - Wikipedia, the free encyclopedia) will come close to our Solar System relatively soon in astronomic scale. This will definitely cause some objects to change their trajectories.
    4) Complex sequences of the above mentioned reasons.

    The trajectories can change from their 'casual' trajectory in Oort cloud to:
    1) Another trajectory in Oort cloud.
    2) Escape trajectory from our Solar System. That is into interstellar space.
    2.1) Escape trajectory that goes through our solar system. (Its inner part.)
    3) Elliptic trajectory of a periodic comet.

    P.S.
    Object from an interstellar space could be 'caught' by some star. There is a hypothesis about origin of this object: http://en.wikipedia.org/wiki/2008_KV42
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  14. #13  
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    Blas

    You answered my query with your wiki reference about capture from interstellar space. Answer me another, if you would. On comets.

    To my limited knowledge, most comets come quite close to the sun (inside Earth orbit) Are there objects from the Oort Cloud that are thrown into orbits that stay well out - say Mars orbit or further?
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  15. #14  
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    Quote Originally Posted by skeptic View Post
    Blas

    You answered my query with your wiki reference about capture from interstellar space. Answer me another, if you would. On comets.

    To my limited knowledge, most comets come quite close to the sun (inside Earth orbit) Are there objects from the Oort Cloud that are thrown into orbits that stay well out - say Mars orbit or further?
    1. Google for list of periodic comets.
    2. My search led me to this Wikipedia list (List of periodic comets - Wikipedia, the free encyclopedia)
    3. As it doesn't show perihelion, let us use heuristics. Search for comets with sufficiently long period.
    4. A very brief search gave me these two comets: 38P/Stephan, 13P/Olbers - Wikipedia, the free encyclopedia.

    P.S.
    This is a better candidate:
    http://en.wikipedia.org/wiki/132P/He...an%E2%80%93Alu
    Also you may reason in other way: If a comets lasts long enough to appear in the list :-), it should vaporize slowly. Obviously you shouldn't take this heuristics seriously.
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