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. 43(8), 1287-1298.
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