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Three different, thick copper targets (an as-received, 98 μm grain size containing ∼1010 dislocations/cm2 (Vickers hardness of 0.89 GPa); an annealed, 124 μm grain size containing 109 dislocations/cm2 (Vicker's hardness of 0.69 GPa); and a 763 μm grain size containing 109 dislocations/cm2 (Vickers hardness of 0.67 GPa) were impacted with 3.18 mm diameter ferritic stainless steel projectiles at nominal velocities of 0.7, 2 and 5 km s-1. Like companion experiments utilizing soda-lime glass projectiles (Part I), absolute grain size of the target was observed to be less important than the dislocation density in the cratering process. At low impact velocity, depth/diameter ratios were observed to increase dramatically in contrast to less dense soda-lime glass impactors, and the impactor behaviours were also very different. The ferritic stainless steel impactors spalled into small fragments at or above 2 km s-1 impact velocity and a significant fraction of these fragments remained in the craters. No significant melt phenomena were observed either in connection with projectile fragmentation or in the crater-related, residual microstructures. Dynamic recrystallization, dislocation cell structures and microbands were significant microstructural features in the targets. They extended from the crater walls and contributed to hardness profiles within the cratered targets. These hardness profiles and actual hardness zones generally increased in extent from the crater wall with both impact velocity and projectile density.

IT is generally believed that the main fraction of dust in the interplanetary medium is generated by the gradual disintegration of short-period comets in the inner Solar System1,2. Analysis of interplanetary dust-grains is, accordingly, a technique for gathering information on the nature of cometary matter. Until now, however, no particle with an unarguable interplanetary origin has been subjected to detailed chemical analysis.