Why planets instead of asteroid belts or rings?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Dinosaur, Oct 12, 2005.

  1. Dinosaur Rational Skeptic Valued Senior Member

    It does not seem intuitively obvious why we have an asteroid belt and planets. Gravitational collapse of a rotating dust cloud suggests to me a large central mass and a thin disk as the end result.

    An asteroid belt or a Saturn-like ring seems more likely than a planet.

    It seems even more difficult to imagine how a binary star system forms.

    BTW: In triple star systems, are the paths of the three stars in a single plane?
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  3. Lucas Registered Senior Member

    Before the formation of planets, the circumstellar disk was alike to an asteroid belt, full of little rocks. These rocks coalesced to form planetesimals, and planetesimals coalesced to form planets

    This is gravity in action. Zones where the concentration of rocks were higher than usual, were the seeds where planets formed

    When the Sun started to give off energy, most of little rocks and dust of the disk that hadn't form planets were expelled
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  5. Dinosaur Rational Skeptic Valued Senior Member

    Lucas: What you say seems reasonable, but what kept the asteroid belt from forming into a planet? In our solar system, formation of planets seems to have been more likely than the formation of asteroid belts.

    Intuition suggests to me that planets or belts form at distances where the rotational speed of a disk of gas and small objects matches the orbital speed as determined by a coalescing central mass. This seems to explain the formation of an asteroid belt. It might explain the formation of several larger objects orbiting at the same distance separated by 90 to 180 degrees of arc.

    Do current theories suggest that planets form from a rotating disk without the formation of an intermediate stage like an asteroid belt? This seems unlikely. If an asteroid belt forms first, why should two groups of small objects on opposite sides of the central mass coalesce into a single large object?

    Why should a binary system evolve rather than a single central mass? Binary systems seem too common to have occurred due to collisions or close encounters, which seem like rare occurrences.

    I assume that in triple star systems, the three stars rotate in a single plane. Is this true?
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  7. invert_nexus Ze do caixao Valued Senior Member

    I forget the particulars, but I believe chaos theory is what you're looking for.

    The planets form in specified orbits where the resonance of orbiting particles match... or something. It's been years since I've read on this. Like I said, I forget the particulars. It's an avenue for you to investigate however.
  8. Lucas Registered Senior Member

    The blame is on Jupiter. According to "Ask to an Astrophysicist":


    Astronomers believe that the strong gravitational field of Jupiter continuously disturbs the motions of these chunks of primitive matter, nudging and pulling at them, thereby prohibiting them from aggregating into a planet
    Last edited: Oct 14, 2005
  9. URI IMU Registered Senior Member

    The Universe has few laws,
    it seems to me that past cosmology just makes up any reasonable mechanism that seems to fit.... so there is an accretion mechanism.... that is reasonable for some observations but totally inadequate for most of the others.

    A fission mechanism covers all aspects of cosmic body formation, position, and structure, IMO.
  10. Lucas Registered Senior Member


    I wasn't sure about this, but I've consulted it to another person, and that person tells me that is not always the case. The example offered is that the orbital plane of 33 Lib BC is different from the orbital plane of 33 Lib A(BC).
  11. Ophiolite Valued Senior Member

    And what is fissioning? And how did it come to be in the first place?

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