Mineralogy and defect microstructure of an olivine-dominated Itokawa dust particle: evidence for shock metamorphism, collisional fragmentation, and LL chondrite origin

摘要: We report here detailed analytical scanning and transmission electron microscopic investigations on an olivine-dominated dust particle (RB-QD04-0042) from the surface of asteroid 25143 Itokawa. The was returned to Earth by Hayabusa spacecraft made available in context first announcement opportunity for sample investigation. Multiple thin slices were prepared precious means focused ion beam thinning, providing a unique three-dimensional access its interior. 40 × 50 μm sized olivine contains spherical diopside inclusion intimate intergrowth troilite tetrataenite. compositions (Fo69Fa31) (En48Wo42Fs10), as well high Ni content sulfide-metal alloy, indicate LL ordinary chondrite origin accord with previous classifications. Although no impact crater exists at RB-QD04-0042, microscopy revealed presence various shock defects constituent minerals. These are planar fractures [001] screw dislocations olivine, multiple {101} deformation twins tetrataenite basal (0001) stacking faults troilite. diagnostic indicators occur only small zone one concave side characterized fracture density. observations can be explained collisional event that spalled off material particle's surface. Alternatively, itself could spallation fragment into larger regolith target. This suggests Itokawa particles lacking visible microcraters their surfaces might have still experienced metamorphism involved fragmentation resulted formation regolith.