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Stardust in Antarctic
micrometeorites.
Yada T., Floss C., Stadermann F. J., Zinner E., Nakamura
T., Noguchi T., and Lea A. S. (2008)
Met. & Planet. Sci., in press.
ABSTRACT
We report the discovery of presolar silicate, oxide
(hibonite) and (possibly) SiC grains in four Antarctic
micrometeorites (AMMs). The oxygen isotopic compositions of
the eighteen presolar silicate (and one oxide) grains found
are similar those observed previously in primitive
meteorites and interplanetary dust particles, and indicate
origins in oxygen-rich red giant or asymptotic giant branch
stars, or in supernovae. Four grains with anomalous C
isotopic compositions were also detected.
12C/13C as well as Si ratios are
similar to those of mainstream SiC grains; the N isotopic
composition of one grain is also consistent with a
mainstream SiC classification.
Presolar silicate grains were found in three of the seven
AMMs studied, and are heterogeneously distributed within
these micrometeorites. Fourteen of the 18 presolar silicate
grains and 3 of the 4 C-anomalous grains were found within
one AMM, T98G8. Presolar silicate-bearing micrometeorites
contain crystalline silicates that give sharp X-ray
diffractions and do not contain magnesiowüstite, which
forms mainly through the decomposition of phyllosilicates
and carbonates. The occurrence of this mineral in AMMs
without presolar silicates suggests that secondary parent
body processes probably determine the presence or absence of
presolar silicates in Antarctic micrometeorites.
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