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

[Sterling K. Webb]

Hi, All,

    Wow! Radical new theory... Not! This 
simulation takes two Big Hits to get rid of 
Venus' Moon(s) and slow the planet to a 
rotational crawl, but this theory...
    Malcuit, R. J., and Winters, R. R., 1995, 
Numerical simulation of retrograde gravitational 
capture of a satellite by Venus: Implications 
for the thermal history of the planet: Abstracts 
Volume, 26th Lunar and Planetary Science 
Conference, Lunar and Planetary Science 
Institute (Houston), p. 829-830.
    ...takes only one satellite and no hits to 
achieve the same result. 

    See Robert Malcuit's webpage at:
http://www.denison.edu/geology/malcuit/_malcuit.html

    Essentially, his computer simulation/theory is this:
Venus captures a retrograde satellite (like Neptune 
does with Triton) early in its life. The retrograde 
satellite slows the planet's axial rotation as it spirals 
in for about 3.5 billion years. This is the opposite 
of what happens with a prograde satellite, which
speeds up the planet and causes the Moon to move 
out, like the Earth Moon system.

    When it gets down to a very close orbit, it heats 
and melts the crust and some of the mantle, then 
breaks up at the Roche limit and pummels the planet, 
completely re-surfacing it and de-gassing all the 
carbonates to produce the CO2 atmosphere we 
see there today. This scenario matches (roughly)
the crater dated age of the Venusian surface (480 
million to 560 million years old).

    Malcuit has apparently been running successful
simulations of satellite captures for over twenty 
years, including a Venus satellite. He doesn't care
for the "satellite by impact" theory to account for 
everything. One reads that "capture" can't happen,
but that may be wrong since he has a successful 
computer model of it. I don't know. But, of 
course, a giant impact could form a retrograde 
satellite instead of a prograde one if it hits just right. 
And then everything would follow as above. 

    There is lots of evidence of some major impact
event in the inner system about the time Venus gets
re-surfaced. You could certainly call the Fall of a
Moon a major impact! The flux of meteorites to the 
Earth increases manyfold for a short time period 
around 420 million years ago. All tektites show an
original formation age of 440 +/- 50 million years.
The Earth suffered its worst ice age ever 535-565
million years ago. It also seems to have made some
rapid changes in its obliquity (axial tilt) during that
time (from the weight of the ice).

    In other words, something big was going on
between 420 and 560 million years ago. Not on the
scale of the Late Bombardment, but involving many
substantial objects. Perhaps that event, whatever it 
was, created a population of big impactors in the
inner system for the Earth to deal with, like the 
Ordovician terminal event ~440 mya, the Permian 
terminal event ~250 mya, the Cretaceous terminal 
event ~65 mya, not to mention the 3 to 5 major
extinction events in the Cambrian.

    A Moon makes a big mess when it breaks up
and falls to its death. In the gravitational disruption
of a satellite, many objects would escape the planet.
The "leftovers" from such a breakup of a Moon, 
though a small percentage of its mass, could be both
numerous and contain some sizeable objects, as big 
or bigger than any inner system debris in billions of 
years. The size of a (presumed) Permian impactor,
the biggest thing to hit the Earth in 100's of millions
of years, would have been about 30 miles, a tiny tiny
fragment of a Moon!

    And like so many essentially similar ideas, I'll bet 
that Alemi and Stevenson never heard of Malcuit 
and Winters.


Sterling K. Webb
-------------------------------------------------------
----- Original Message ----- 
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Tuesday, October 10, 2006 6:06 PM
Subject: [meteorite-list] Venus May Have Once Had A Moon


> 
> 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.