CORRECTED CHEMICAL SIGNATURES IN STARDUST GLASS REVEAL WILD 2 PARTICLES THAT RESEMBLE MATRIX GRAINS OF AGGREGATE IDPs

Introduction: The Stardust mission obtained the first dust samples in the coma of an active comet for laboratory analyses. Earlier chemical data on dust from an active comet came from the GIOTTO and VEGA missions to comet Halley [1]. For decades aggregate interplanetary dust particles (IDPs) were available from parent bodies other than those of meteorites [2], i.e. comets or comet-like bodies. Comet Halley and aggregate IDPs consist of nanometer scale entities that include ultrafine-grained and coarse-grained principal components (PCs), GEMS, Mg-rich olivine and pyroxenes, and Fe,Ni-sulfides [3]. Hypothesis & Model: Similar entities define the “weakly constructed mixtures of nanometer scale grains’ of comet Wild 2 but grains with these entities were iso-chemically modified during hypervelocity capture whereby all original petrological properties were lost except silicates >500 nm and ‘FeS’ grains >100 nm [4-7]. However, their bulk chemical signatures were preserved in vesicular Si-rich glass with numerous ~1 to ~100 nm Fe-Ni-S inclusions. Melting and mixing of nanometer scale Wild 2 grains and silica melt is represented in a mixing diagram Fe and Mg both as a function of Si (el%) (Fig. 1); Mg represents the “silicate” fraction assimilated in Si-rich glass and Fe represents the numerous Fe-Ni metal and Fe-Ni-S compound grains (dotted lines) that precipitated from immiscible sulfide melts.