INTERSTELLAR OXIDE GRAINS FROM THE TIESCHITZ ORDINARY CHONDRITE

MOST material in the Solar System has an isotopic composition that represents an average of the different stars that contributed material to the protostellar cloud. Primitive meteorites, on the other hand, preserve grains that retain the isotopic signatures of their individual stellar sources(1) and thus provide valuable insight into stellar and galactic evolution, nucleosynthesis, and solar nebular processes. A large number of pre-solar silicon carbide, graphite and diamond grains have now been isolated(1,2), but only three interstellar oxide grains have hitherto been recovered(3-7), even though oxygen-rich stars are believed to be the dominant source of dust in the Galaxy(8,9). We report here the isolation of 21 interstellar oxide grains from the Tieschitz meteorite. The grains exhibit a wide range of oxygen isotope compositions, indicating that they originated in several distinct stellar sources having different masses and initial compositions. There is also evidence for the presence of the short-lived radionuclide Al-26 in nine of the grains at the time they formed. Although the isotopic compositions of many of the grains are consistent with both observations and theoretical models of oxygen-rich red giant stars, a significant fraction have no observed stellar counterpart.