[meteorite-list] New, long, Carancas article II

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 5 Apr 2008 01:44:56 -0500
Message-ID: <064801c896e8$8fec0d50$8250e146_at_ATARIENGINE>

Hi,

A hypersonic shock front, or "bow-wave," has
strong boundary properties; it doesn't transmit
heat well. True, it can heat a meteorite up hot
enough to melt rock, but that's only 2200 degrees,
while the plasma just one centimeter in front of
the rock is 8000 degrees (or 14,000 or 30,000,
depending on speed, mass, etc.) So, really not
much heat is being leaked. Really, it's only being
radiated.

What Schultz is counting on is the fact that the
shock wave is bent back along an elongated object
but never gets close enough to the sides to heat
them. Picture a space capsule, like the Mercury one.
The shielding is all on the blunt front; the sides
(which taper in) are just plain lightweight metal.
The sides never even got scorched in that fiery
re-entry!

So, the front of a long shape meets the air "head-on,"
takes all the heat and ablation, while the plasma
streams backward, angled slightly away from the
sides. In the "Schultz" model, the shock wave encloses
a train of fragments all jammed up against the shock
front and held together longitudinally by deceleration
and transversely by shock compression. In the
"Webb" model, the meteoroid is just a big old long
rock, but its long sides don't get ablated either, by
the same mechanism. In both versions, only the
front gets ablated.

It's obvious to me from the shock features of Carancas
that this is a stone that has been hammered very hard
in several points in its life history. It is the remains of some
larger object that was really whacked hard. Violent
impacts produce more irregular fragments than gentle
impacts. It doesn't seem a stretch that the Carancas
meteoroid would have an irregular shape, like a long
"splinter" of rock.

What do we know about the shape of meteoroids before
they enter the atmosphere? Simple. Next to nothing. Is
everything in the universe a soccer ball? No.

There is this paper that claims that a mathematical analysis
of the distribution of sizes of fragments found in a meteorite
fall can reveal such details as the number of breakups the
object went through or if the shape of the original body
deviated from the spherical. (This used to be free access...)
http://www.iop.org/EJ/article/0295-5075/43/5/598/node4.html
by L. Oddershede (Technical University of Denmark ),
A. Meibom (University of Odense, Denmark ) and J. Bohr
(Hawai'i Institute of Geophysics and Planetology, University
of Hawai'i at Manoa).

They studied a number of strewnfields and found some
to be the result of a single fragmentation event and some
to be the result of multiple fragmentations. The equations
also imply the original shape. The Mbale Object (they say)
was almost spherical while the original Sikhote-Alin
meteoroid was a long cylinder at least 3-4 times longer
than wide: a big iron splinter. I think (based on modeling
speeds) Carancas was 4-5 times longer than wide.

Carancas has a tendency to fracture along the dark
shock veins (or slickensides, if that's what they are).
Any rock that has a preferred cleavage, for whatever
reason, is unlikely to have been broken into a sphere.
I wish somebody would try to isotopically date the
shock features of Carancas. I bet it has a history...


Sterling K. Webb
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----- Original Message -----
From: <star-bits at tx.rr.com>
To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
Cc: <meteorite-list at meteoritecentral.com>; <meteoriteguy at yahoo.com>
Sent: Saturday, April 05, 2008 12:44 AM
Subject: Re: [meteorite-list] New, long, Carancas article II


It would seem to me that if the stone fragmented in flight and was contained
by the shock wave it would still be heated by the plasma and all the
fragments would develop crusts. There appear to be some pieces with crust,
but enought to match Schultz's theory?

---- "Sterling K. Webb" <sterling_k_webb at sbcglobal.net> wrote:

    Schultz and I both agree that a greater aerodynamic
efficiency will get a chondrite to the ground faster with
less loss of material, making an impact like Carancas
possible.

    What Schultz proposes is that the fragile material of
Carancas fragmented early on but did not "pancake" out
and cause an airburst, but was wrapped by the shock wave
around the hypersonic meteoroid into a "bullet" shape
that stayed together and kept its high speed to the ground.

.... What I proposed was that the Carancas impactor was an
elongated fragment to begin with. That is, it was a "sliver" of
asteroid that was 4 or 5 times longer than its width when it
entered the Earth's atmosphere. The results would be the
same: a faster trip to the ground in (mostly) one piece.

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Received on Sat 05 Apr 2008 02:44:56 AM PDT