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I Oort cloud.

  1. Jun 2, 2016 #1
    I know this has been suggested because of long period comets.
    Sort of a spherical asteroid belt at the very edge of where the Sun's gravity has any relevance.
    The inner asteroid belt, and the Kuiper belt though have many examples of objects which are proof that they exist.
    Is the Oort cloud any more just fairly reasonable speculation?
     
  2. jcsd
  3. Jun 2, 2016 #2

    mathman

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    Gold Member

    The main evidence for the existence of the Oort cloud s the trajectories of comets.

    from wikipedia
    In 1932, the Estonian astronomer Ernst Öpik postulated that long-period comets originated in an orbiting cloud at the outermost edge of the Solar System.[7] The idea was independently revived by Dutch astronomer Jan Oort as a means to resolve a paradox.[8] Over the course of the Solar System's existence the orbits of comets are unstable and eventually dynamics dictate that a comet must either collide with the Sun or a planet or else be ejected from the Solar System by planetary perturbations. Moreover, their volatile composition means that as they repeatedly approach the Sun, radiation gradually boils the volatiles off until the comet splits or develops an insulating crust that prevents further outgassing. Thus, Oort reasoned, a comet could not have formed while in its current orbit and must have been held in an outer reservoir for almost all of its existence.[8][9][10]

    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. All long-period comets have very large orbits, on the order of thousands of AU, and appear from every direction in the sky.[10] Oort noted that there was a peak in numbers of long-period comets with aphelia (their farthest distance from the Sun) of roughly 20,000 AU, which suggested a reservoir at that distance with a spherical, isotropic distribution.[10] Those relatively rare comets with orbits of about 10,000 AU have probably gone through one or more orbits through the Solar System and have had their orbits drawn inward by the gravity of the planets.[10]
     
  4. Jun 2, 2016 #3

    fresh_42

    Staff: Mentor

    What I find disturbing is the fact, that we think the Oort Cloud exists and is still related to our sun, but this doesn't prevent us from calling the Voyagers' current positions interstellar at about 111 AU, 135 AU resp. It will take them another 6,000 years to reach it (20,000 AU assumed).
     
  5. Jun 2, 2016 #4
    I can see where the reasoning comes from.
    However is it not possible that very long period comets are just small bits of interstellar material that never were part of the solar system, or any other system, just loosely bound frozen gases (including water)
    (Not a personal theory, just a question)
     
    Last edited: Jun 2, 2016
  6. Jun 3, 2016 #5
    It's called interstellar space because that's where the interstellar winds are dominate. The sun becomes as insignificant as every other star. The Oort cloud is only bound to the sun because it's the closest strong source of gravity, other than that, it's essentially an interstellar object, the sun has no effect on it.
     
  7. Jun 3, 2016 #6

    phyzguy

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    If comets were falling in from interstellar space, you would expect most of them to have eccentricities greater than 1, indicating that they are not bound to the solar system. In practice I think (not sure) that most long period comet eccentricities are less than 1, or at most equal to 1 within experimental uncertainty.
     
  8. Jun 3, 2016 #7
    Thanks everyone.
     
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