[meteorite-list] Venus May Have Once Had A Moon

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Wed Oct 11 15:58:02 2006
Message-ID: <20061011195759.32034.qmail_at_web50906.mail.yahoo.com>

I've been saying this for years. I even tell my
classes.

If log angular momentum is plotted vs log Mass, all
planets fit nicely on a line except Venus and Mercury
(Earth/moon system needs to be combined).
Now since angular momentum is a conserved quantity, it
matters not one jot how far a planet and its moon
drift apart. Combine the angular momentum of Venus and
Mercury and they slot nicely on the line like all the
others.
If some accuse me of favouring an idea which is too
neat, I'd accuse the author of this article of this
article of over-thinking a problem. The peculiar
rotation of venus is rather nicely explained by it
losing a moon, especially one as big as Mercury.

Rob McC
(plagariser of his Professors Ideas)

--- Ron Baalke <baalke_at_zagami.jpl.nasa.gov> wrote:

>
> http://skytonight.com/news/4353026.html
>
> Why Doesn't Venus Have a Moon?
> by David Tytell
> Sky & Telescope
> October 10, 2006
>
> Back when Earth was very young, our home world was
> steadily pummeled by
> large solar system debris. While Earth withstood the
> barrage of hits
> like a prizefighter that wouldn't fall down, one
> blow nearly destroyed
> the world. A Mars-size body plowed into us,
> completely disrupting both
> bodies and splashing massive amounts of debris into
> orbit which, most
> astronomers agree, coalesced to form our Moon.
>
> But if something that large hit us, how did our
> nearest-neighbor planet,
> Venus, dodge the same fate? According to a new
> study, it didn't.
> Billions of years ago, according to work announced
> yesterday, Venus once
> had a moon that formed the same way Earth's did.
>
> On Monday at the American Astronomical Society's
> Division of Planetary
> Sciences meeting in Pasadena, California, Caltech
> undergraduate Alex
> Alemi presented models created with David Stevenson
> of Caltech that
> suggest Venus was not only slammed with a rock large
> enough to form the
> Moon, the event happened at least twice.
>
> According to Alemi and Stevenson, in models of the
> early solar system it
> is nearly impossible for Venus to avoid a big hit.
> Most likely, Venus
> was slammed early on and gained a moon from the
> resulting debris. The
> satellite slowly spiraled away from the planet, due
> to tidal
> interactions, much the way our Moon is still slowly
> creeping away from
> Earth.
>
> However, after only about another million years
> Venus suffered another
> tremendous blow, according to the models. The second
> impact was opposite
> from the first in that it "reversed the planet's
> spin," says Alemi.
> Venus's new direction of rotation caused the body of
> the planet to
> absorb the moon's orbital energy via tides, rather
> than adding to the
> moon's orbital energy as before. So the moon
> spiraled inward until it
> collided and merged with Venus in a dramatic, fatal
> encounter.
>
> "Not only have we gotten rid of the moon, but we've
> also done well to
> explain Venus's current slow rotation rate [and
> direction]," says Alemi.
> If a second moon formed from the second collision,
> it too would have
> been absorbed the way the first one was.
>
> The models do allow for more than two impacts, but
> the probability of
> Venus enduring several massive collisions is low.
> "You can do this with
> multiple collisions, but the hypothesis is that [the
> net result] adds up
> to a negligible contribution" to the planet's final
> state, says Alemi.
>
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Received on Wed 11 Oct 2006 03:57:59 PM PDT