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High abundances of circumstellar and interstellar
C-anomalous phases in the primitive CR3 chondrites QUE 99177 and MET
00426.
Floss C. and Stadermann F. J. (2009)
Astrophys. J., 697, 1242-1255.
ABSTRACT
QUE 99177 and MET 00426 are the first known CR3 chondrites and
have largely escaped the aqueous alteration experienced by most of the
CR chondrite group. In addition to high presolar silicate and oxide
grain abundances, these meteorites also contain high abundances of
phases with anomalous C isotopic compositions. Presolar SiC abundances
(~65 ppm) are consistent with independent estimates for CR1 and CR2
chondrites, indicating that aqueous alteration does not destroy SiC,
but are significantly higher than earlier abundance estimates based on
noble gas contents. Particularly notable are the high abundances (~120
ppm) of carbonaceous matter with anomalous C isotopic compositions that
probably formed in cold molecular clouds via ion–molecule reactions.
The observation of both 13C-enriched and 13C-depleted
compositions
suggests that multiple chemical pathways contribute to the formation of
this material. The abundance of such material is significantly higher in
QUE 99177 and MET 00426 than in other primitive meteorites and attests
to the primitive nature of the CR3 chondrites.
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