[meteorite-list] Allende vs. Nakhla (delete if dull)

From: David Weir <dgweir_at_meteoritecentral.com>
Date: Thu Apr 22 09:52:13 2004
Message-ID: <3D5AAD33.BD81BC_at_earthlink.net>

Hello Ron, List,

While I was speculating about an extended (33+ km) strewn field for
Nakhla, which is inferred by the dog impact story, Ron suggested a
comparison with the 48 km long Allende strewn field might be in order. I
agree:
_____________________________________

ALLENDE -- Thousands of individual stones fell, creating the largest
stone strewn field recorded, measuring 50 km in length and at least 300
kmē in area. The largest recovered specimen was found eight months after
the fall by Guadalupe Juarez as he was hunting a rabbit. The meteorite
created a crater 32 inches by 52 inches and 13 inches deep, having a
small rim on the north end. This specimen was estimated to have weighed
~110 kg before it was fragmented upon impact with the hard soil. The
total recovered weight of the Allende fall was over 2,700 kg, a record
for stone meteorites that is surpassed only by the Jilin, China fall in
1976 of ~3,600 kg.
________________________________

Theoretical models I have seen do not help to constrain the
probabilities of an extended strewn field for Nakhla. For instance,
according to the same "non-peer-reviewed" paper by Eugster et al. that I
referenced yesterday (the minimum preatmospheric mass for Nakhla was
established at ~150 kg), model calculations predict the upper limit of
fragments ejected from Mars to be ~90,700 kg. Based on a 50% to 80%
ablation rate, the final mass could have been as large as ~18,000 to
~45,000 kg, respectively, plenty large enough to produce a strewn field
extended into Denshal and beyond. Based on this maximum ejection mass,
one could also expect a much larger inundation of black stones in the
surrounding area.

After judging the usefulness of the above data to the issue at hand, I
would rather interpret the pre-atmospheric mass of Nakhla from a
reality-based model, rather than from a poorly-constrained theoretical
one. One such reality-based model was constructed for the Shergotty
mass, with a pre-atmospheric mass value calculated at 26 kg. This comes
from well-established, peer-reviewed research. Unfortunately, this is
the only such case that I uncovered in the literature, and may not be
analogous to Nakhla, but it encourages me in reasoning that any
comparison of the fall of Allende to that of Nakhla is probably
unreasonable.

David
Received on Wed 14 Aug 2002 03:19:15 PM PDT