[meteorite-list] fire flies or flying fires

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Mon Jun 27 19:49:15 2005
Message-ID: <42C09053.A6FBAB04_at_bhil.com>

Hi,

    Again, it's all in the timing. But you made me re-think some things. Like
Newton, you form no hypotheses. I, on the other hand, am a hypothesizing fool.

    If the Moon is a molten liquid drop of uniform density (undifferentiated),
then Earth's gravity distorts it into a spheroid, and cooling and
differentiation take place in an egg-shaped Moon, creating a thick equatorial
crust and thin polar crust with a centered core until the Moon is cooled. So, it
didn't happen that way.

    So, it was only when mass concentrated toward to the Moon's center (after at
least partial differentiation) that the warm gooey center was tugged and shifted
toward the Earth, moving easily in the hot liquid and slush.

    Now the internal heat has two different length of cooling paths to nearside
and farside centers. The nearside cools faster and the mantle crystallizes
sooner: thinner crust. The farside cools more slowly and the crust continues to
thicken until the mantle separates: thicker crust. As the interior stiffens up,
it forces the off-center core back, almost but not all the way back, towards the
center.

    But I'm worried about my little pet theory, It doesn't look so healthy as
it did last night (more research). There are spots in Crisium where the crust
thickness is essentially zero and north of Korolev it's up to 107 km thick.
That's a little extreme. The Moon is, to generalize, lumpy and uneven, and the
crust differential, which I had always though of as relatively uniform, is far
from it. There are spots on the farside where the crust is as thin as the
thickest parts of the nearside crust. My pet theory might have to go the pet
theory hospital...

    This argument depends on a fully locked rotation rate from the very start.
The fact is, we don't know about that. There are no clues. Present librations
and precessions are all accountable for by gravity and orbital parameters; there
are no residual motions. 4500 million years is a long time...

    Even the truly odd thing, the Moon's orbital inclination to the Earth, can
now be accounted for by the collision model as presently refined. It seems the
debris disk's gravity waves can incrementally crank up the inclination to 15
degrees or more (and the Moon's is only 5).

    Interestingly enough, for this scenario to work, they say, the Moon has to
accrete on the outermost edge of its accretion disk around the Earth, which
would certainly account for nearside preferential impacts. (That one just fell
in my lap!)

    I think accretion in orbit virtually guarantees a lock. The Moon is orbiting
initially very, very close to the Earth, and we outweigh the opponent 80 to one.
The fight is fixed. The smart money is down.

    But the model, in its present highly tweaked state, is still primitive. Its
equation of state, which underlies the whole thing, is crude and simplistic,
says Jay Melosh. Currently, the model only works if the Big Impact happens while
the Earth is still assembling, at about half its present mass, and Moon
formation is part of the accretion process.

    This puts it on the timeline at about 4530-4540 mya. A breathing space for
the happy zircon? If impact happens later, there's too much angular momentum in
the system for it to work unless you compensate with a larger and larger
impactor.

    Oddly enough, after last night, I was thinking about angular momentum.
(Really, I was, that's why it's odd.) There really is no reason why any
terrestrial planet should any angular momentum to speak of. Accrete a planet by
rocky impacts with totally randomized force vectors and you get NO residual
angular momentum. Everything cancels out (always neat). The giant planets,
formed by a different mechanism than rocky accretion, all spun up nicely, the
bigger the faster.

    Mercury and Venus have very little angular momentum. It's pitiful. Mars has
more. My theory on that is that Mars accreted on the inner edge of a reduced
accretion disk because the newly fattened-up Earth Moon system was increasingly
stealing of Mars' planetesimals on the sunward side. Because Mars accreted more
from the outward side, the impact vectors were prograde preferential and added
angular momentum to the Mars system.

    Maybe our Big Impactor was the largest proto-Mars planetesimal and we stole
it. Maybe the Earth was trudging toward being a small warm dry planet and Mars
was on the road to being big and wet and cool, teeming with life and firmly
believing itself to be the Center of the Universe, when suddenly, its glorious
destiny was snatched away by that sneaky little Earth!

    No wonder the Martians hate us! That's probably why they're always doing
that War of the Worlds thing of theirs. They're only reclaiming what was
rightfully theirs... Being minds "vast and cool and unsympathetic," as Wells
says, their superior computer simulations have demonstrated it to be true beyond
all possible doubt.

    With planet-wide super-cooled quantum-state computers, their equation of
state is so refined that they can trace the Big Impactor back toward Mars orbit.
"It's ours! The Earthlings stole it!" they say, wiggling those three fingers in
righteous indignation.

    The Earth's angular momentum is truly colossal. Having that lunar
counterweight, light as it is compared to the Earth's mass, out there on a long,
quarter million mile lever arm does it, just as Jupiter holds most of the
angular momentum in solar system.

    I imagine cranking up the Act Of God Machine and instantaneously snatching
the Moon out of orbit and putting Mars in an identically configured orbit, only
further in, since Mars weighs about eight times what the Moon does.

    I'm still scribbling on the back of a really big envelope when the Act Of
God Machine abruptly fires, having adjusted all the parameters with an accuracy
of +/- 100 microns, and POP!

    There's Mars, covering more than 10 sky degrees, like a Great Pumpkin! Mars
Rise and Mars Set are spectacular beyond belief! The month is less than two
weeks long. The light of a Full Mars is not only bright enough to read by at
night but as bright as a dim overcast day. And the surf and tides are amazing --
SURF'S UP! all the time.

    The trip to Mars is now a breeze. If you can't afford the ticket, you can
sit in your back yard with an inexpensive amateur telescope and spot the dust
clouds being raised by the construction of Marineris City by our huge machinery.
Over in the night hemisphere, the lights of Newer York sparkle like stars on the
planet's face. The Moon is gone.

    Angular momentum is perfectly conserved.

    I read in the newspaper (by Marslight) that, despite the recent treaty, the
Martians are starting to grumble about the hot wet air and the noise pollution
again. What they griping about? If this deal was so bad, why are there so many
Martian tourists everywhere you go? You should see the lines at McDonald's! And
at SpaFon's too! There are lots of Martian businesses on Earth now that we
explained money to them. They seem to like money just fine, if you ask me.

    Note: the price of "Martian" meteorites has plummeted again, and are clearly
headed to way below a dime a gram. The Martians just fill their pockets with
pretty rocks from their back yards and sell'em to brokers or trade'em for taxi
rides whenever they make the short hop to Earth. The price of Lunaites is WAY
up, though.

    Then the big machine's screen blinks, "What do you want me to do with the
Moon? It's starting to get pretty hot here in stasis!" I tell the Act of God
machine to put it in a very close orbit around Venus, so it can start spinning
up the planet, a dry moon for a dry world. I make a note to myself for the next
time I feel like cranking up the Act Of God machine, "Do something about Venus."

    Yup! Definitely got to do something about Venus...


Sterling K. Webb
------------------------------------------------------------------
Chris Peterson wrote:

> Hi Sterling-
>
> Yeah, I guess you're right, we're doomed to disagree <g>. (Did you see the
> cleverly packaged MIT T-shirts distributed to MIT freshman at last years
> orientation? The ones that nobody noticed until too late had "Because not
> everyone can go to Caltech" printed on the back?)
>
> I take exception to your point that the Moon "obviously" has a uniform crust
> early on. This isn't obvious at all, and nobody has a good explanation for why
> the Moon does not now have a uniform crust. This feature does not fall out of
> any models. Gravity does not obviously explain why the crust should
> be thinner towards the Earth. If the crust thickness variation developed early
> (and the maria are certainly old) this would explain the reason that maria are
> only present on one side. Since it is likely that the Moon was not yet tidally
> locked when the basins formed, I don't see the effects of the Earth as having
> contributed in an obvious way to their formation.
>
> Chris
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
Received on Mon 27 Jun 2005 07:48:35 PM PDT