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Fwd: Re: KT Bolide--Comet or Meteorite?

Bill Keel's correction of my earlier posting lacks a CC to the list, but 
he and I are unsure whether he sent it separately. If this is a 
duplicate, the fault is mine. My post, based on statements in Alvarez's 
Crater of Doom book, erroneously assumed that a comet would vaporize on 
impact, leaving no evidence. Hence the comet argument was unfalsifiable. 
I don't want to perpetuate that wrong interpretation, so I asked Bill if 
I could forward his reply.  
George J. Leonard
Prof. of Interdisciplinary Humanities
San Francisco State University 

---------------- Begin Forwarded Message ----------------
Date:        01/25  7:01 AM
Received:    01/25  1:08 PM
From:        William C. Keel, keel@bildad.astr.ua.edu
To:          gl91bciiLt@earthlink.net

Since comets contain small solid particles which are identical to meteors
(in fact constituting shower meteors after the are liberated from the 
cometary nucleus), the distinction from fossil evidence may or may not
be possible. Large amounts of nickel/iron meteoritic debris would
likely rule out a comet, since such metallic meteors apparently came
from breakup of bodies that were big enough for internal melting and
differentiation. We know a bit about the composition of cometary
meteors, from spectroscopy as they are heated (and often destroyed)
upon reaching the atmosphere, plus looking at samples of dust collected
at high altitudes. They are by and large like carbonaceous
chondrites, the leat chemically-processes kind of meteor(ite),
which is in fact the abundance pattern reported by Kyte for the
putative K-T meteorite fragment. For those deeply interested,
meteor spectra are described by Millman in _Comets, asteroids, meteorites_
(Lyon, 1977), plus some others that I can't quote just now because
the Astrophysics Data System (http://adsabs.harvard.edu) has somehow
just gone offline from our site. Anyway, the 2-mm reported object
would be big but not unheard of for a cometary inclusion - and
for a comet, the Chixulub event would have been extraordinarily
large and thus have a corresponding grain population. I suspect
there hasn't been as much discussion as you'd think on which
it was, because to first order only total impacting mass and
velocity with respect to Earth matter in the enery released and
in the forms of collateral damage done.

Bill Keel
Astronomy, University of Alabama

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