[meteorite-list] Re: Rubble pile asteroids

From: Herbert Raab <herbert.raab_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:31 2004
Message-ID: <fa3612e2e.12e2efa36_at_utanet.at>

Bob Verish writes:
> I have described it as being a loose rubble pile of
> L6, L5, and L4 meteoroids; held together by the most
> minimum of gravitational attraction. How else can you
> explain a strewn field of stony meteorites with such a
> variation in metamorphic grade, yet NO EVIDENCE of
> brecciation, meaning that each individual stone is
> either all L6, or all L5, or all L4, but never a
> combination of the three?

I am not so sure if this is a strong indication that the
Gold Basin meteorid was a rubble pile. If a rubble pile
meteorid closes in on Earth, it will probably be disrupted
by tidal forces *before* it enters the atmosphere. Maybe
you would get a strewfield very similar to a strewfield
produced by a compact meteorid that breaks up at in the
atmosphere. Or maybe not, and the strewfield would be
different (i.e., larger strewfield, no aerdynamic sorting
of the meteorites by size, etc.). I don't know...

On the other hand, the real border between a L5 and a L4
or L6 might be more blurry than the descriptions in the
textbooks suggest. There is an interesting paper on the
Dar al Gani region in the August 2002 issue of MAPS. The
authors conclude that pairing based on class, shock level
and weathering grade is problematic, because individual
speciemns from ordinary chondrite strewfields were assigned
to different classes. Either this is another strong
indication for frequent rubble pile meteorids, or maybe
we just see the fuzzy borders between petrographic types
of meteorites. Who knows? I certainly don't... ;^)

Best greetings,
  Herbert
Received on Wed 25 Sep 2002 09:37:06 AM PDT