[meteorite-list] Lunar capture theory

From: Tom aka James Knudson <knudson911_at_meteoritecentral.com>
Date: Thu Apr 22 10:21:03 2004
Message-ID: <01f501c34816$c48f1e60$17c743d8_at_malcolm>

Hello List, Does any one know the estimated time of the creation of the
asteroid belt? From what I understand, the theory is, that it was once a
planet that was destroyed by a collision? I am wondering if the moon, how
ever it was formed could be a result of the asteroid belts collision?
Thanks, Tom
Peregrineflier
The proudest member of the IMCA 6168
----- Original Message -----
From: Sterling K. Webb <kelly_at_bhil.com>
To: Meteorite-List (E-mail) <meteorite-list_at_meteoritecentral.com>
Sent: Friday, July 11, 2003 6:09 PM
Subject: Re: [meteorite-list] Lunar capture theory


> Hi,
>
> Howard's already pointed how hard (and unlikely) capture is. Before
the
> capture theory was popular, the theory was fission: that the Moon split
off from
> a rapidly spinning early Earth. While this may sound whacky today, the
theory
> had a lot going for it.
> First, the density of the Moon as a whole is exactly the same as the
bulk
> density of the Earth's crust to within less than 1% difference. Wow, how
could
> that be coincidence?
> Second, the tidal action of the Moon is enlarging it's orbit, slowly
moving
> the Moon further away and lengthen the month. If you run this progression
> backwards, you end up with a Moon in contact with the Earth's crust and
the
> Earth's equator spinning at a speed just a hair faster than orbital
velocity!
> And third, there is this <bleep>ing big hole in the side of the Earth
called
> the Pacific Ocean whose excavated volume is roughly Moon-sized (1-1/4% of
> Earth)!
> Hey, sounds pretty good, don't it?
> This theory was still going strong up to about 1950. The author of
this
> theory was Charles Darwin. No, not THAT Charles Darwin. His nephew (or was
it
> grandnephew? can't remember).
> The density WAS a coincidence.
> The tidal equations run backward, once you have a computer to do the
> crunching, reveal that there are unstable oscillations in the Moon's orbit
that
> limit how close the Moon could ever have been.
> Since continents move and oceans spread, the Pacific Ocean basin is
not an
> ancient feature of the Earth.
> Bang! One Dead theory.
>
> The problem with James'"slow capture" theory is that the more we learn
about
> planetary accretion, the more it looks like the final stages of big
> planetesimals (1000 km objects) growing to bigger planets at last goes
wizz-bang
> FAST. And, the Earth and the Moon are SO different, that it's impossible
to
> imagine them both forming in the same region of the solar nebula. One of
us
> doesn't belong here...
>
> The impact origin of the Moon, if true, is an unbelievably messy
> complication. We would like to be able to extrapolate from the Earth's
> composition the composition of the planetesimals at this distance from the
Sun,
> but if the Earth is partly made up of some rogue Mars-sized impactor that
came
> from somewhere else in the system, well, you can toss all that research
out of
> the window! Because the Earth would no longer be representative of this
> neighborhood in the nebula.
> Well, why can't we figure out from the Moon's composition where in the
solar
> system it came from and learn about the composition of the solar nebula
there?
> O, yeah, take a planet and smash it into dust and gas and let recondense.
Where
> have all the volatiles gone? Were there any volatiles to begin with? Are
all
> those refractories in the Moon the result of them surviving the impact, or
was
> the Moon rich in those refractories to begin with? (The Moon should be
called
> Titaniumville, and I have no doubt that someday some burg on the Moon will
be
> named just that, maybe in Chinese...)
> Maybe the Earth is so rich in water (instead of being "normal" like
Venus)
> because it captured all the volatiles from the ur-Moon. Maybe the Earth
had
> oceans 80 kilometers deep BEFORE it got whacked with a <bleep>ing planet
and
> this little bit of water is all that's left!
> And then there's the core. We have always assumed that the Earth's
core is a
> native feature of the planet, but if the Moon impactor theory is correct,
some
> percentage of the Earth's core is really the Moon's core, captured by the
> heavier Earth in the impact. That means it can't be a "normal" core
(whatever
> the H*** that is) and we can't know how "normal" the other terrestial
planets'
> cores are. Maybe the Earth is the only planet with tectonics because it
has this
> extra big core? (Personally, I think it's the extra water, but...)
> You see, this impact thing just messes up everything!
>
>
> Sterling K. Webb
> --------------------------------------------------------------------------
----------
>
> Ken O'Neill wrote:
>
> > Hi List,
> >
> > Would there be anything in the geological comparison between Earth and
Moon
> > that would lean toward the "capture" rather than "same debris" theory or
> > vice versa ?
> >
> > Regards
> >
> > Ken O'Neill
> >
> > -----Original Message-----
> > From: meteorite-list-admin_at_meteoritecentral.com
> > [mailto:meteorite-list-admin_at_meteoritecentral.com]On Behalf Of Tom aka
> > James Knudson
> > Sent: 11 July 2003 21:48
> > To: Matson, Robert; meteorite-list
> > Subject: Re: [meteorite-list] Lunar capture theory
> >
> > Hello Robert and list, My understanding of planet formation in a
nutshell is
> > that debris orbiting the Sun gradually merged and formed planets. Right?
> > Why couldn't two bodies have formed from the same debris in the same
> > orbit and orbiting around the sun together in the same direction and the
> > same orbit, Gradually the Moon slowly caught up with the earth and got
> > caught up in the earths gravity? Or the earth came up behind the Moon
and
> > captured it?
> >
> > Thanks, Tom
> > Peregrineflier
> > The proudest member of the IMCA 6168
> > ----- Original Message -----
> > From: Matson, Robert <ROBERT.D.MATSON_at_saic.com>
> > To: meteorite-list <meteorite-list_at_meteoritecentral.com>
> > Sent: Friday, July 11, 2003 1:01 PM
> > Subject: [meteorite-list] Lunar capture theory
> >
> > > Tom wrote:
> > >
> > > > I do not believe the moon was made by a asteroid impact on the
> > > > earth.
> > >
> > > What, specifically, about this theory bothers you?
> > >
> > > > I would first stand by the theory that it was caught up in our
> > > > gravity.
> > >
> > > While this is a ~possible~ scenario, you have to understand how
> > > extremely unlikely graceful capture is compared to impact.
> > > The capture idea also has a difficult time explaining why the
> > > Moon doesn't have a normal-sized core for a body of its size,
> > > which the impact theory explains nicely. Finally, why the
> > > oxygen-isotope similarity of earth and the Moon if the two
> > > bodies formed in different parts of the solar system?
> > >
> > > Prior to the Apollo sample return missions (and the discovery
> > > of our beloved lunar meteorites), the capture theory at least
> > > had some wobbly legs to stand on. But O-isotope analysis of
> > > the moon rocks knocked one leg out, and the other leg was swept
> > > away by Lunar Prospector's confirmation that the moon's core
> > > comprises less than 3% of the moon's mass.
> > >
> > > --Rob
> > >
> > >
> > >
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> > >
> >
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Received on Fri 11 Jul 2003 09:41:50 PM PDT