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Are orbital planes generally parallel on large scales?

  1. Nov 3, 2011 #1
    The moon orbits the earth on nearly the same plane as the earth orbits the sun. Does this coincidence of orbital planes scale up? Do the planets in our solar system orbit on a plane that is parallel to the plane of the milky way? What about planets in other solar systems in the milky way?
  2. jcsd
  3. Nov 3, 2011 #2
    I believe due to gravitational and rotational effects, spinning fluids (or dust clouds, a.k.a. proto-planetary systems) tend to stretch into disk shapes perpendicular to the axis of rotation of the cloud. On something the scale of the milky way however, this won't happen because the time it takes for a considerable revolution is too large even on a solar scale.

    And no our planets don't, if they did the ecliptic would line up with the milky way, which it doesn't.
  4. Nov 3, 2011 #3


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    The ecliptic is about 40 degrees out of alignment with the plane of the milky way.
  5. Nov 4, 2011 #4

    D H

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    In our solar system, the planets and many of the asteroids orbit along more or less the same plane. The minor planets such as Pluto and the major moons orbit along a similar plane. The solar system apparently formed in a nice, orderly fashion. Some other star systems apparently did not. Scientists have observed exoplanets with highly inclined and even retrograde orbits.

    Planetary systems form because the interstellar cloud from which the star formed already had some angular momentum. This angular momentum causes the cloud to form an accretion disk; the planets form in this accretion disk. A solar system such as ours results if the formation is nice and orderly and unperturbed. Unchecked planetary migration and perturbations from nearby stars can result in systems with widely varying inclinations, planets kicked out of orbit, etc.

    As far as where the angular momentum comes from: Some of it came from the star that exploded and formed the gas cloud. Stars passing nearby this cloud can transfer angular momentum to the cloud due to gravity gradient torque. The gravity gradient torque from the galaxy is rather small, making for a very small correlation between the orientations of the galactic plane and that of the planetary system.

    It's about 60 degrees, not 40.
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