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Could a collision cause Venus to rotate prograde?

  1. Aug 23, 2007 #1
    I got in an argument and I was defending one of the theories about Venus' slow prograde rotation. I'm defending the theory which states that atmospheric friction, over a period of billions of years slowed initially fast rotation of Venus and made it go prograde.

    My opponent says that it would only be possible as a result of collision with a body three times larger than the moon in early Solar System formation.

    My point is that such a collision could disintegrate both of the bodies and after all the matter condense it would be subjected to tidal forces of the sun (due to its proximity) and orbital energy cause the protoplanet to start rotating counterclockwise.

    Please help me with that.
  2. jcsd
  3. Aug 23, 2007 #2


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    Venus has a retrograde orbit.
    It's slow rotation period is exactly what you would expect for a planet with a thick atmosphere cleaose to the sun and subject to tidal locking.
    It may have had surface liquids earlier in it's history which would have speeded up the tidal friction.
  4. Aug 24, 2007 #3


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    I don't know much about this, unfortunately, but a bit of research shows that it may be possible to explain Venus' rotation without a planetisimal impact.

    The mere publication of this theory doesn't mean that this is necessarily the right answer though. I'm afraid I don't know what the "consensus" view is, or even if there is a consensus.

    For an example of a published peer-reviewed version of the non-impact theory, see for instance http://adsabs.harvard.edu/abs/2003Icar..163....1C, available online at http://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus1.2002.pdf

    One interesting quote:

    Apparently the authors are saying that the naive "tidal lock" where Venus presents one face to the sun one would expect becomes unstable for a planet with a thick atmosphere (!).

    I'd like to balance this out by finding a peer-reviewed published version of the impact theory, but so far I haven't found one (though I've seen plenty of popular references).
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