Stardust's carbon heat shield ablation: carbon vapor condensates

Frans Rietmeijer, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM
Carbon condensation typically requires C/O >1which means that ablation of elemental carbon materials in an oxidizing atmosphere would not be expected to yield carbon-vapor condensates. The atmospheric C/O ratio is ~9 x 10-4, which implies a >1100 times C-enrichment factor. During deceleration of the Stardust capsule I expect that carbon atoms and ionized species will react with atmospheric oxygen and nitrogen, while a small fraction of the heat shield will also be released as carbon fragments. Close to the capsule‰Ű(tm)s surface, and probably varying at different locations, carbon enrichments may produce conditions where C/O >1 required for the condensation of elemental carbon solids. I will show examples of the types carbon solids that might have formed on the capsule‰Ű(tm)s surface. Such condensed solids might include poorly graphitized carbons, C60 and higher fullerenes, carbon nanotubes and onions, graphite, carbynes, and nanodiamond. When any or all of these solids condensed from a carbon vapor, mapping the distributions of different carbons on the surface might offer qualitative insights in flow patterns, vapor density and temperature fluctuations near the surface of the decelerating STARDUST capsule.