[meteorite-list] Carancas paper

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 18 Jun 2008 22:29:13 -0500
Message-ID: <037d01c8d1bc$a5e38f70$8d5ae146_at_ATARIENGINE>

Hi, Katsu, List,

    Thanks for the link to this paper.

    As for the paper itself, I find it basically
unbelievable. Using today's substitute for
actual science, the mathematic model computer
simulation, they "solve" the problem of the
Carancas meteoroid by hypothesizing that it is
"monolithic" (without any structural weaknesses)
and of an abnormally strong material.

    Of course, if they had ever tested or even
looked at the Carancas material, they would have
seen that the exact opposite is true. Carancas is
weak, friable, and riddled with shock veins, melts,
slickensides (Elton says, with evidence). Carancas
is so weak it must be handled carefully.

    Someone must have pointed this problem out to
the authors. This quotation from the very end of the
paper is their answer:

    "The meteorites recovered close to the crater were
reported to be fragile (N??ez del Prado et al. 2008).
The meteorites cannot be, however, considered to
reflect the properties of the original meteoroid in this
respect, since the material was subject to strong shock
during the actual impact and may have been reduced
almost to powder."

    The notion that impact and subsequent fragmentation
miraculously transforms the meteoritic substance
unrecognizably is an unique idea, has never proposed
before, and strikes me, frankly, as idiotic. Please, explain
to me how the 50,000+ fragments of Sikhote-Alin, for
example, differ from the original iron meteoroid? The
physical properties of the 50,000+ fragments are identical
to each other and identical to other, unfragmented
meteorites of the same type.

    When a fragment is produced from the shock of impact,
it is most likely from the "back" of the impactor. At impact,
the shock wave proceeds forward into the impacted surface
and backward through the meteoroid. Assuming impact is
energetic enough, at the front of the meteoroid, material is
vaporized. Further back, material is melted. Further back still,
material is reduced to a powder (that's the norm for catastrophic
failure in stone). At the very rear of the impactor, the shock
wave detaches fragments.

    All the meteorites recovered from any impact are
essentially these detached fragments. Detachment occurs
when the shock wave reaches a plane of weakness, a
shock vein or other feature that cleaves, allowing the escape
of the fragment. The point that's important here is that
escaped fragments have not yet experienced the passage
of the shock wave at the time they escape, only the mild
shock of detachment.

    The only evidence in Carancas of rock vapor or melt
is in the products of the ablation trail. The crater and its
vicinity was liberally dusted with rock powder in large
quantities. There were large, multi-kilo fragments, mostly
scooped up in the first few days by scientists (and not avid
meteorite dealers) from INGEMET and the Bolivian university
who were the first on the scene. These large fragments are
the most representative of the meteoroid; there is nothing
in the reports published about these fragments to suggest
anything like monolithic strength.

    As a result, the surviving fragments, which are ALL
the meteorites produced from the impact, have NOT
been "subject to strong shock during the actual impact."
Intact detached fragments are absolutely and completely
representative of the original physical properties of the
meteoroid.

    I judge the "monolithic hypothesis" to be a fairy tale.
Extraordinary claims demand... well, you know. They
claim a strong monolithic material. When confronted with a
weak non-monolithic fragment of their supposed monolith,
they wave their hand, "Oh, it's been magically transformed!"

    That's pretty extraordinary.


Sterling K. Webb
---------------------------------------------------------------------------------
----- Original Message -----
From: <ohtsuka at jb3.so-net.ne.jp>
To: <meteorite-list at meteoritecentral.com>
Sent: Tuesday, June 17, 2008 8:25 AM
Subject: [meteorite-list] Carancas paper


Hello list members,

I have just downloaded a free PDF file of the letter paper on the Carancas
event,
published in A&A yesterday. This seems to be very interesting and the
link is below:

http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2008/26/aa09905-08/aa09905-08.html

Katsu
Tokyo, JAPAN

------------------------------------------------------

A&A 485, L1-L4 (2008)
DOI: 10.1051/0004-6361:200809905


Letter
The Carancas meteorite impact - Encounter with a monolithic meteoroid
J. Borovicka and P. Spurn?

Astronomical Institute of the Academy of Sciences, Fricova 298, 25165
Ondrejov Observatory, Czech Republic
    e-mail: borovic at asu.cas.cz

Received 4 April 2008 / Accepted 4 May 2008

Abstract
The formation of a 13-m wide impact crater by a stony meteorite near
Carancas, Peru, on September 15, 2007 was an unexpected event. Stony
meteoroids usually disintegrate in the atmosphere in many pieces, each
landing at low velocity. We present examples of well-observed fireballs,
which have all experienced atmospheric fragmentation. Using a simple model,
we find that the Carancas meteoroid may have avoided fragmentation, if its
strength was 20-40 MPa; such a strength would be comparable to the tensile
strength of stony meteorites, but is higher than the strength of other
observed meteoroids. We conclude that Carancas was a rare example of a
monolithic meteoroid that was free of internal cracks. This example
demonstrates that meteoroid strength can vary significantly from case to
case and does not depend on meteoroid size. We estimate that the initial
size of Carancas meteoroid was 0.9-1.7 m. Our model predicts an impact
velocity that w
as in the range 2-4 km s-1.


Key words: meteors, meteoroids -- Earth

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Received on Wed 18 Jun 2008 11:29:13 PM PDT