Analytical scanning and transmission electron microscopy of laboratory impacts on Stardust aluminum foils: interpreting impact crater morphology and the composition of impact residues

摘要

The known encounter velocity (6.1kms-1) and particle incidence angle(perpendicular) between the Stardust spacecraft and the dust emanating from thenucleus of comet Wild 2 fall within a range that allows simulation inlaboratory light gas gun experiments designed to validate analytical methodsfor the interpretation of dust impacts on the aluminum foil components of theStardust collector. Buckshot of a wide size, shape and density range ofmineral, glass, polymer and metal grains, have been fired to impactperpendicularly upon samples of Stardust Al1100 foil, tightly wrapped ontoaluminium alloy plate as an analogue of foil on the spacecraft collector. Wehave not yet been able to produce laboratory impacts by projectiles with weakand porous aggregate structure, as may occur in some cometary dust grains. Inthis report we present information on crater gross morphology and itsdependence on particle size and density, the pre-existing major and traceelement composition of the foil, geometrical issues for energy dispersive X-rayanalysis of the impact residues in scanning electron microscopes, and themodification of dust chemical composition during creation of impact craters asrevealed by analytical transmission electron microscopy. Together, theseobservations help to underpin the interpretation of size, density andcomposition for particles impacted upon the Stardust aluminum foils.