[meteorite-list] Pairing ?-Type Asteroids to OC's (from Arkansas)

[mexicodoug at aim.com]

Hi Listees:

There may be a little more going on here than this quickly published 
note with such a glorious title "Discovery of the Source of the Most 
Common Meteorites".  It seemed a little odd and quickly put together.  
Probably is some good work, but ... I see next week at the Asteroids, 
Comets and Meteors Meeting,

http://acm2008.jhuapl.edu/

is the following paper:

PHYSICAL CHARACTERIZATION OF VERY YOUNG ASTEROID FAMILIES. P. 
Vernazza1, R. P.
Binzel2, A. Rossi3, M. Birlan4, S. Fornasier5, M. Fulchignoni5, S. 
Renner6.

http://www.lpi.usra.edu/meetings/acm2008/pdf/8044.pdf

In which the Datura and other families have their spectra taken and 
studies.

Hmmm ... sounds like someone may be looking for some extra press a few 
days before the ACM meeting.  Vernazza, Binzel, et al group has done 
the spectra up to 2.5 microns and looks like a much more comprehensive 
work.

Also in my original comments, I mentioned S-Type Asteroids.  I take 
that back until it can be confirmed - from the press release they may 
be Q-Type a stony sub-group (with metal), and uncommon subcategory.  
Time will shortly expose more of this if it hasn't already.

Best wishes,
Doug





I wrote:

http://www.sciencedaily.com/releases/2008/07/080710103903.htm 
 
The press release was confusing to me at first, highlighting the 
Fayetteville H4 (fall, Arkansas) meteorite. Perhaps they did because of 
being fresh and closer to the surface (?) in the parent body model. Not 
sure why the 1270 Datura family, etc., would be expected to be from the 
relatively rarer surface of the original parent body vs more common 
heat altered interior). 
 
In any caseit seems they are NOT claiming that (1270) Datura is the 
parent body to any of our meteorites (how could it be - don't virtually 
all ordinary chondrites have CRE's of floating around as meteoroids 
well over 1 million years?) 
 
However, it seems they are pointint out that because it is an S-type 
asteroid that has apparently suffered a collision only 450,000 years 
ago(which was shown by other researcher a studying the probabilities of 
members' orbits couple of years ago), it gives an opportunity to study 
fresher material of this most common high silicate asteroid type by 
telescopic spectroscopy, and they had an opportunity to take the 
spectra. I guess they only look at the 0.5 and 1 um peak because it is 
more sensitive to space weathering (?), but this isn't too clear 
either. (the authors didn't extend it to the typical 2.5 microns where 
some good stuff is visible - at least not in figure in the press 
release). 
 
In any case, their proposed contribution seems that they measured 
spectra of theyoung Datura family and compared it to ordinary chondrite 
spectra and got a better match than ever before helping to solve the 
conjecture that the common asteroid class (second only to supposed 
carbonaceous chondrites typed asteroids) should be paired to common 
meteorites. Hopefully they make a case for a trend in asteroid 
reflectance spectra vs. age, vs. a one hit wonder, but there still seem 
to be more complexities to be ironed out regarding what meteorite is 
appropriate to compare to what asteroid in the clan, IMO. Maybe 
Fayetteville was just selected because it is what they had access to... 
Article sounds like it will be a good one. Comments? 
 
Best wishes, Doug 
 
PS Interestingly, Wikipedia (at this moment - no doubt it will be fixed 
by someone reading this) says the Datura cluster formed 450 MILLION 
years ago and a probable source of zodiacal dust.... Maybe Wikipedia 
can't be trusted yet again, once the dust has settled :) 
 
 
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