[meteorite-list] Serious question and CD Spheroids

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:57 2004
Message-ID: <DIIE.000000440000115E_at_paulinet.de>

> The iron impactor disintegrated and spread iron all over the planet in
> a fallout cloud and created a layer of iron rich material on the surface.

> My knee-jerk reaction to that is to think about the large iron meteorites
> in our collections. They tend to be the most competent and coherent
> and hence will hold together on impact. It doesn't seem likely to me
> that an iron will disintegrate in the fashion you are talking about on
> impact. I'm not sure of that just my first reaction to the statement.

Hi List,

LEYA I. et al. (2002) Pre-atmospheric depths and thermal histories of Canyon
Diablo spheroids (MAPS 37-7, 2002 July, pp. 1015-1025) - Introduction:

The impact of the Canyon Diablo (IAB) projectile peppered the soil around
Meteor Crater with millimeter-sized spheroids consisting mainly of metallic
Fe and Ni (Nininger, 1956). Nininger speculated that the spheroids condensed
from a vapor cloud as fiery rain. Several authors have argued against this
speculation (Kelly et al., 1974; Blau et al., 1973; Mittlefehldt et al., 1994),
suggesting instead that the spheroids formed from a liquid generated either
by atmospheric friction and/or by shock melting on impact.

We wanted to find out more about the quantity and location of projectile material
that melted to form spheroids. From sampling data, Nininger (1956) estimated a
total spheroid mass of 4000 to 7500 metric tonnes, roughly 5% of the impactor.
More recently, E. Pierazzo determined through theoretical modeling calculations
that a 1 to 2 m cap on the trailing surface of the projectile would have remained
solid (Schnabel et al., 1999). This result is consistent qualitatively with several
other lines of evidence, namely, an earlier theoretical treatment (Bjork, 1961),
which showed that a reflected shock wave would shear (solid) meteorites off the
rear surface of the projectile; track measurements, which show that despite heavy
ablation, numerous meteorites consist of fragments that originated near the pre-
atmospheric surface (Bhandari et al., 1980); and experimental results for noble
gases in Canyon Diablo meteorites (Heymann et al., 1966), which indicate pre-
atmospheric depths of <2 m.

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Received on Thu 18 Sep 2003 10:37:19 AM PDT