[meteorite-list] Shatter-cones on Itokawa

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 21 Apr 2007 21:21:52 -0500
Message-ID: <068f01c78484$fe451c00$862e4842_at_ATARIENGINE>

Hi, Chuck, List,

    A shatter cone is a solid rock that has been
cracked, creviced, fissured by a shock wave that
originates at a single point, so all the cracks are
aligned so that they point to the source of the
shock wave. The rock may not be completely
shattered or if it is, it may be re-fused by the
heat and pressure after it is cracked. But the
pattern shows a convergence.

The surface of Itokawa is jillions of little pieces
(and medium and big pieces, too) that align with
the local weak gravity to point (as I understand it)
toward the deepest parts of the "saddle," where
gravity is weakest, the local "downhill." In both
cases, the pattern is a converging one.
    "In other signs of downhill movement, the
pea-size grains tended to point sideways, as
though they had been rolling, and boulders
had clusters of the small ones piled behind them,
implying that big rocks blocked the movement
of smaller ones."
    Being jiggled by even a one-centimenter impactor,
Itokawa must quiver all over, like an asteroid with
a chill!

    In both cases, we have features that demonstrate
alignment with a force that originates in a point: the
impact point in the case of a shatter-cone, and the
effective focus of a celestial body's gravity. On tiny
Itokawa, we can see that gravity converges to a
point. On Earth, we have the illusion that "down is
down" because the planet is so large.
    For centuries, opponents of a "round" Earth,
pointed out that folks on the opposite side of the
planet from sensible folk would, of course, fall
right off the world (like Australians)! It was called
the Problem of The Antipodes. The obvious
solution is that gravity is a Central Force Field,
an answer that didn't occur to anyone for millennia.
    But if you were standing in London with a plumb
bob pointing straight down and I were standing in my
Illinois house with a plumb bob pointing straight down,
watching each other connected by closed circuit TV,
we would agree that both plumb bobs were effectively
parallel. But in reality, they would be at a 90 degree
angle to each other.
    On Itokawa, if we were near the saddle, we could
see that we were standing at various funhouse angles
to each other.
    It's a Small World!

Sterling K. Webb
----- Original Message -----
From: Charles O'Dale
To: meteorite-list at meteoritecentral.com
Sent: Friday, April 20, 2007 6:56 AM
Subject: [meteorite-list] Shatter-cones on Itokawa


Some of these rocks "look like" they have the shatter-cone pattern on them.

Compare to a Manicouagan shatter-cone.


Charles O'Dale
Ottawa RASC

-----Date: Thu, 19 Apr 2007 18:03:40 -0400
From: Mal Bishop <magbish3 at lowcountry.com>
Subject: [meteorite-list] Asteroid Jiggles Like a Jar of Mixed Nuts
To: meteorite-list at meteoritecentral.com
Message-ID: < at lowcountry.com>
Content-Type: text/plain; format=flowed; charset=us-ascii

"Like a jiggled jar of mixed nuts, shaking on the near-Earth asteroid
Itokawa is sorting loose rock particles
on its surface by size, causing the smallest grains to sink into
depressions, a new study suggests. ..."


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Received on Sat 21 Apr 2007 10:21:52 PM PDT

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