Circumstellar aluminum oxide and silicon carbide
in interplanetary dust particles.
Stadermann F. J., Floss C., and Wopenka B. (2006)
Geochim. Cosmochim. Acta 70, 6168-6179.
A systematic NanoSIMS isotope imaging study of
sub-micrometer phases in interplanetary dust particles
(IDPs) has led to the discovery of two presolar grain types
that previously were observed only in primitive meteorites.
A 350 nm x 600 nm Al2O3 grain has a
large 17O enrichment and a slight 18O
depletion, as well as a 26Mg excess due to the
decay of extinct 26Al. Because of its relatively
large size and prominent location within the IDP, this
presolar Al2O3 grain is well
characterized by SEM-EDX analyses. A second, much smaller
presolar grain has a diameter of 150 nm and a 13C
enrichment of more than 300%. Isotopic anomalies in C are
rarely found in IDPs and the magnitude of this anomaly is
unprecedented. This grain also has a 15N-rich
composition and its isotopic makeup as well as its secondary
ion yields identify it as a SiC grain.
The discovery of presolar Al2O3 and
SiC in IDPs seamlessly complements earlier notions of
interplanetary dust particles as the most primitive
extraterrestrial material currently available for laboratory
analysis. Both Al2O3 and SiC are
common presolar grain types in primitive meteorites, but
they appeared conspicuously absent from the presolar grain
inventory in interplanetary dust particles, which is
dominated by silicate stardust. Not finding these
presolar grain types in interplanetary dust would have been
difficult to explain. Abundance estimates of the new
presolar grain types in IDPs are hampered by limited
statistics, but both Al2O3 and SiC are
less common than presolar silicates which have been found at
relatively high abundances in IDPs. The particle in which
these presolar grains have been found belongs to the
'isotopically primitive subgroup' of IDPs, yet does not
contain any presolar silicates.