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Re: mars and venus



Even though I am an amateur astronomer, and I teach an introductory
astronomy course, I am no expert. Aren't there some true astronomer
types on this list who can help us out. If not, here's what I thought
I knew.

My understanding, and all the books I have, would disagree with David
Bowman and John Mallinckrodt. I don't understand what isn't right with
John's simulation.

If the solar system had some original angular momentum, and barring
collisions, the angular momentum has to be conserved as planets form.
I suppose a planet could take on a retrograde rotation if its
revolution, or some other object's angular momentum in the solar
system, would assume the opposite change. But I don't see the
mechanism for that to happen.

If the forming planet is acting like a gravitational sweeper to clear
out mass from some volume in the vicinity of its orbit, the mass from
the outer orbital radii will have higher orbital angular momentum and
the mass from the inner orbital radii will have lower orbital angular
momentum. But because there is more mass coming from the outer radii
(there's more volume there) the planet is going to have to rotate
prograde rather than retrograde in order to conserve angular momentum.

The astronomy books I have all say that Venus (and Uranus) must have
begun prograde and then suffered some sort of collision.


Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817