Association of Presolar Grains with Molecular Cloud Material in IDPs

Anhydrous interplanetary dust particles (IDPs) collected in the stratosphere appear chemically, mineralogically, and texturally primitive in comparison to meteorites. Particles that escape significant atmospheric entry heating have highly unequilibrated mineralogy, are volatile element rich, and, overall, appear to have escaped significant parent body hydrothermal alteration. These IDPs are comprised of the building blocks of the solar system. The strongest evidence that anhydrous IDPs are primitive is that they contain abundant stardust and molecular cloud material. In particular, presolar silicates were first identified in IDPs and are present in abundances (450-5,500 ppm) that are well above that observed in primitive meteorites (less than 170 ppm). The most fragile (cluster) IDPs also commonly exhibit large H and N isotopic anomalies that likely originated by isotopic fractionation during extremely low temperature chemical reactions in a presolar cold molecular cloud. The D/H ratios exceed that of most primitive meteorites, and in rare cases reach values directly observed from simple gas phase molecules in cold molecular clouds. The most extreme D- and N-15-enrichments are usually observed at the finest spatial scales (0.5-2 microns) that can be measured. These observations suggest that D and N-15 hotspots are in fact preserved nuggets of molecular cloud material, and that the materials within them also have presolar origins. The advanced capabilities of the NanoSIMS ion microprobe now enable us to test this hypothesis. Here, we report two recent examples of presolar silicates found to be directly associated with molecular cloud material.