Presolar dust grains from meteorites and their stellar sources

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Primitive meteorites contain small concentrations (ppb to ppm) of presolar dust grains that have survived largely unaltered the processes that led to the formation of the solar system. Minerals identified to date include diamond, silicon carbide (SiC), graphite, silicon nitride (Si3N4), corundum (Al2O3), spinel (MgAl2O4), and possibly titanium oxide (TiO2). These grains exhibit large isotopic anomalies indicative of a stellar origin. Variations in the isotopic ratios of the major elements and of many trace elements contained in the grains range over more than 4 orders of magnitude. The presolar dust grains preserve memories of both nucleosynthesis in the parent stars and galactic chemical evolution. Most of the silicon carbide and corundum grains formed in the winds of red giant and asymptotic giant branch stars. Most graphite grains, some SiC and corundum grains, and all silicon nitride grains originated most likely in supernova ejecta. A few SiC and graphite grains appear to have a nova origin. The origin of the diamonds is still unknown but at least a small fraction apparently comes from supernovae. Diamonds are only 2 nm in size. The other types of presolar grains are larger and range from ≈ 0.2 to 20 μm. These sizes are larger than those inferred for dust in the interstellar medium but are comparable to the sizes of interstellar dust in the heliosphere identified by the Gallileo and Ulysses spacecraft missions.