[meteorite-list] Good read about the moon being captured byEarth

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 19 Dec 2010 01:31:08 -0600
Message-ID: <8DE077AFF2554DF3A917BFDC3BB9EC5B_at_ATARIENGINE2>

Hi,

First of all, I think that Capture Phobia (fear that
a planet might capture a satellite) is essentially
irrational. It is clear that such a thing can (and HAS)
happened: No one thinks that Deimos and Phobos
were formed "along with" Mars (in place). They're
Captures. There is little doubt or discussion that
RETROGRADE satellites are Captures. These include
Triton, the 15th largest body in the solar system,
20% bigger than Pluto. Capture.

When it comes to the large planets and their satellites,
the convention is to blithely assert they were "formed
in place." Miniature solar systems with their own miniature
solar system formation? Show me the model for that process.
Well, the truth is that no one has been able to successfully
model that assumption. It is a dead fish of an idea that
nobody sniffs.

So, we really don't know how the MAJORITY of solar
system satellites got where they're at. We DO assume
they've been there, with their planets, for a very long
time, since the early system. So, how DO you get small
rocky satellites to form around a Gas Giant AFTER every-
thing, including gasses, has already been swept up?

I have cited Malcuit in various List posts over the decade.
I dug them out but most of the old links are Kaput. I
suggest you look at his home page at Denison University:
http://www.denison.edu/academics/departments/geosciences/malcuit_r.html
He discusses his work and lists publications... but
link-free. There's a section on the "Cool Early Earth"
and whether it's a problem for his simulations.

Malcuit has spent most of his calculation on the heat
generated and how it's dispersed and by which body,
and whether a "cool" capture is easier than a "hot" one,
the role of a planet's "viscosity" in dissipating the energy
of capture... Why don't you read the page?

> Capture theory doesn't address the identical
> oxygen isotope ratios shared by Terra and Luna.
> Nor our 23? axis tilt.

Again, all oxygen isotope ratios tell you is that Earth
and Moon formed in a similar accretion zone, but we
know that. It has no effect on whether it's a Crash or
a Catch. I don't get the link between tilt and capture.
True, a satellite restrains axial tilt from wider swings,
but what has that got to do with how you got the
satellite?

And, quite a part from Malcuit's studies of Capture, there
are other ways a planet can grab itself a moon. The hardest
thing to believe about the "Luna bangs into the Earth and
gets Caught" theory, is that it HAS to be a gentle smack,
hardly more than a graze. Impacts in general are NOT gentle.

There is one way to get a graze, though. If two bodies accrete
in a very similar orbit, the larger will usually eject the smaller,
UNLESS the smaller can slip into a Trojan position in the
orbit. However, if it keeps accreting (or is big enough at the
beginning), it will be perturbed into oscillating back and
forth, approaching the larger body and finally "sliding" up
the orbit to a "gentle" collision with it.

That's kind of a Crash and kind of a Capture, with relative
velocities of only 100's of m/s. Of course, even the "slowest"
touch of planetary bodies will disrupt them. But it might
explain the Earth-Moon Double Planet.

See, a whole NEW Crazy Theory!


Sterling K. Webb
--------------------------------------------------------------------------------
----- Original Message -----
From: "MEM" <mstreman53 at yahoo.com>
To: "Greg Catterton" <star_wars_collector at yahoo.com>;
<meteorite-list at meteoritecentral.com>
Sent: Saturday, December 18, 2010 9:10 PM
Subject: Re: [meteorite-list] Good read about the moon being captured
byEarth


----- Original Message ----
> From: Greg Catterton
> Subject: [meteorite-list] Good read about the moon being captured by
> Earth
> about a year old but a good read and something to consider. I think
> this
>theory is more plausible also.
> Maybe the moon was hit and knocked towards Earth and was captured.

Yeah...BUT.....Capture theory doesn't address the identical oxygen
isotope
ratios shared by Terra and Luna. Nor our 23? axis tilt. Nor the
migration
dynamics to move .88 AU in 100 million years to be in place for the
capture.
According to the article, Malcuit has been working on this for several
decades.
While Malcuit wasn't looking up from his desk, he may have missed the
little
isotope-ratio "thingy".

While some rocks in Australia were dated to 4.0?.03 billion, the claim
for the
oldest earth rocks dated were in the range of 3.8-4.3 billion( a one
half
billion error margin) leaving 400-500million years for the surface to
re-congeal--which the author doesn't think is adequate. The wack
obviously
would have excavated some of the mantle but not necessarily the core. I
haven't
seen the math, so I don't know if the envelope of possibilities allow
for some
deep-crust plutons to have avoided being disrupted. Maybe we need to be
looking
for plutons with giant shattercones rather than micrometer-sized zircon
crystals. Another caveat in this "dating" is it isn't the rocks
themselves
which are that old-- its the un-remelted zircons within them and a giant
wack
would not necessarily have melted every last reservoir of zircon. The
zircons
in Australia were in much younger sandstone.

I'd like to know more about the mechanism of capture to convert a highly
elliptical orbit (which would be likely be passing inside the Roche
radius of
the earth 16 times per year) into an almost circular one. ( I'd like to
hear
more about the wack from the orbit from inside Mercury and how the Moon
would
have retained so much silicate content which should have been boiled
away).
While we know there is a small, permanent, tidal bulge, on the backside
of the
moon, the moon is far far less ellipsoid then predicted given the
perturbations
of the Roche limit would have exerted over part of the 3 billion years
of
stabilizing--AND the moon would have to have been largely plastic-- if
not
molten , for the ellipsoid to become spherical. BUT the moon is missing
compression ridges that would have been left by the tectonics a solid
crust
floating on a plastic lunar mantel. I do agree that the churning would
have
heated both earth and the moon if the moon had survived the capture for
any
length of time--according to this theory. And we have calculated the
rate the
moon is moving away from us such that 400mybp we had 20 hour days. So
where is
the orbital mechanics that got the moon so close and only to let it
assume a
different orbital radius? The mechanism should have been a single
vector not
first one than another.

I would also like to know what these "geologically impossibilities" are
the
author did not elaborate on other than his argument on cooling rates and
the
inferred "earliest age" the zircons could have formed that we use to
date the
oldest rocks. This is the first I've heard that the" Big Wack" was
estimated
to have occurred after the earth had formed oceans.


Finally, some do believe there were a dozen or more bodies in the very
early
solar system that were ejected out of the solar system else were
absorbed into a
body that yet remains. Calculations show that there are resonances and
that
bodies have moved into orbits other than the ones they were formed in
but IIRC
these were largely inward migrations(?). What wacker "knocked" the moon
into a
radical orbit and where is the wacker today?


Seems someone has too much of their life invested in a theory overcome
by events
to accept that it is only a matter of time before the memorial service.
Thanks,
however, was a good read and I think we are open minded enough to weigh
the
facts. Now if I can just get someone to agree with me about cold vs hot
meteorites...

Elton
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Received on Sun 19 Dec 2010 02:31:08 AM PST