[meteorite-list] [ebay] ending in about 2 days

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun Oct 15 19:40:54 2006
Message-ID: <006801c6f0b3$571a9550$a7e68c46_at_ATARIENGINE>

----- Original Message -----
From: "stan ." <laser_maniac_at_hotmail.com>


> http://www.lpi.usra.edu/meetings/metsoc2005/pdf/5218.pdf says that both
> 1839 and 3133 are from the CV parent body

Hi,

    Only a complete fool would poke his nose into
this largely private mess, and here I am.

    There are lots of List subscribers who never
post and who only subscribed to learn something
about meteorites, not human nature.

    A distinction needs to be made between meteorites
from the same parent body and meteorites that are
"paired."

    A "pairing" means that two meteorites or separated
clusters of meteorites are from the same fall: Abstract:
http://adsabs.harvard.edu/abs/2000M&PS...35..393B
and the full article by Benoit, Sears, Akridge, Bland,
Berry, and Pillinger, can be found at:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2000M%26PS...35..393B&amp;data_type=PDF_HIGH&amp;type=PRINTER&amp;filetype=.pdf

    Here's the gist of it:
    "Pairing is the procedure of identifying fragments
of a single meteorite fall, separated during atmospheric
passage or during terrestrial history, by establishing the
similarity of two or more meteorite fragments... Criteria
for pairing can be divided into (1) parent body history
indicators, (2) meteoroid space history indicators, and
(3) terrestrial history indicators... Many literature pairings,
especially those involving common meteorite types,
bear large uncertainties due to lack of data."

    They nicely pinpoint the problems. Two different
meteorites, very, very much alike, could be from two
different meteoroid bodies that were chipped off a
parent body at different times. Or, they could be from
one meteoroid body that suffered a subsequent impact
that fragmented it, and each chunk arrived at the Earth at
different times. Or, they could be from one meteoroid
body that fragmented early in the rough entry to the Earth's
atmosphere and produced a divergent fall, with two
strewn fields. Or, the meteorites could have made one
unified strewnfield only to have an Earthly event, like a
flood, transport part of it to somewhere else.

    They call the problem "non-trivial" which is restrained
scientific talk for "Some of these pairings stink." They come
at the problem from every side, and it's a thick juicy paper,
which also includes an appendix of 390 "pairings," including
a "pairing score" indicating its likelihood to be true. Anybody,
in or out of this quarrel, interested in "pairing" as a general
problem ought to read it.

    Frankly, I don't think buyers are anywhere as excited
about pairings as dealers seem to be. Every chunk of HED
is sold as "coming from Vesta!" In the real world, however,
most of the HED on Earth came from the Vestoids, a collection
of battered asteroids excavated from Vesta (probably from
that big southpole crater almost as big as Vesta itself) that
trail away from Vesta toward a resonance where the jump
to Earth is easy. They didn't come "from" Vesta; they took
the big bus most of the way and jumped off at our stop.
Yet, on the other hand, it's true they "came from" Vesta.

    Coming from the same parent body doesn't mean that
two fragments are the same "type" unless the parent body
is a monotypical body -- some is and some ain't. You can
have multiple "types" coming from the same body. There
can be multiple identical "parent bodies" if an original
single-type "parent body" was "subdivided" by a big
impact, like many members of one asteroidal "family."
And most "parent bodies" are hypothetical entities that
cannot be clearly or certainly indentified with a "real"
body. (That will happen in about two centuries, when
we have gone there often enough.)

    The terms "same parent body," and "same type,"
and "pairing" all have quite different meanings, and
each has its own degree of uncertainty. I have seen
the term "launch pairing" used to mean fragments
derived directly from a single impact on one source
material. All of these terms need refining, and that's
one small step in that direction.

    Now I'm going to belly up to the bar and watch
the rest of this barfight from there (I hope). Go to it,
boys!


Sterling K. Webb
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Received on Sun 15 Oct 2006 07:40:46 PM PDT