[meteorite-list] Where are the shocked H-chondrites?

From: almitt <almitt_at_meteoritecentral.com>
Date: Thu Apr 22 09:37:39 2004
Message-ID: <3A4DC75B.1F5D358C_at_kconline.com>

Hi Bob and all,

>>List member Rhett Bourland and I have been having a little discussion recently about
why there seem to be a fair number of shocked, brecciated L-chondrites (particularly
L6s) vs. relatively few shocked H-chondrites. Did the H-chondrite parent bodies
somehow experience a less violent history?<<

The parent Body for all the H type chondrites seems to be asteroid Hebe! Apparently
Hebe suffered an impact that was rough enough to damage the asteroid to the point of
bringing inner parts of the asteroid to the outside (the higher differentiated
numbers) and mix them on the surface with the lower numbers. The so called rock-pile
effect. It however did not get hit so hard as to have the material escape totally and
it reassembled into the asteroid we see today. Taking spectra we see the various
H6,H5,H4, and H3's as the asteroid rotates which match spectra of the various H type
chondrites we sample here as meteorites.

The L Parent Body had a similar impact (more disruptive) but in this case did not
reaccrete as Hebe did. As a class the L type chondrites are more severely shocked
metamorphosed than other type chondrites (88%). McSween suggests it is much higher
than a typical cratering event. Using argon isotopes it is suggested the event took
place some 500 million years ago. Asteroid 3628 Boznemcova, has a signature similar to
L6 type chondrites and is thought to be a left over relative small fragment from this
event. I also see a similar signature with asteroid Eros with the L4 type chondrites
but we may be talking a different parent body here than what we see left over from
some of the other L's.

Perhaps the good work NASA is doing at Eros as we speak will reveal some parent body
types from that asteroid in the very near future. Best regards.

--AL Mitterling
Received on Sat 30 Dec 2000 06:30:35 AM PST

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