[meteorite-list] Sikhote Question

[bernd.pauli at paulinet.de]

Jeff N. wrote:

"Now I've come across something really interesting: it appears to be a normal shrapnel
fragment, weight 266.4 grams, except it has a very distinct impact pit and splash rim.
It seems to me that an impact pit could only have been formed during flight, meaning
some 'pure' shrapnel pieces must therefore have been created by mid-air fragmentation,
not  explosive fragmentation upon impact."


Hello Jeff N., Jeff K. and List,

Buchwald about this surface morphologic feature:

BUCHWALD V.F. (1975) Iron Meteorites (Univ. of California, 1975, Vol.3, pp. 1123-1130):

Solitary, round-floored circular depressions 1-8 mm in diameter and ringed by high-relief
rims occur on fusion-crusted individuals and on at least one shrapnel fragment.

We interpret these features as impact craters resulting from high-velocity collisions between
meteoritic particles during the * l a t e s t   s t a g e s * of atmospheric flight. Although
crater-like bubbles might develop within a fusion crust, during skin heating by atmospheric
friction, craters emplaced on fusion-free shrapnel fragments had to have formed later, after
atmospheric penetration had already violently disrupted a larger body.

Local conditions during the Sikhote-Alin event included thousands of Fe projectiles infalling
into an environment already populated with high-speed Fe and rock ejecta fragments from craters
still being formed on the ground.


Cheers,

Bernd