Capture of cometary dust grains in impacts at 6.1 km s-1

The NASA Stardust mission to comet 81P/Wild 2 collected grains of cometary dust freshly ejected from the comet during a fly-by at a speed of 6.1 km s -1. These were captured on aluminum foils and in blocks of silica aerogel. The dust underwent a severe shock during capture. The nature of the shock process depends on the properties of the dust and the collecting media. On the aluminium, the shock process and impact damage is typical of that between high-density (or hard materials) at high velocity, resulting in craters lined with impactor residues. The peak shock pressures are estimated at 60-80 GPa. Two main crater types are seen, simple bowl shaped and multiple pit craters: these reflect the degree of consolidation of the original dust grain. Capture in the low density aerogel was via a more gradual slowing of the dust grains accompanied by a variety of effects on the grains (complete break up of weak grains vs. ablation of well consolidated grains). The relation between the structure of the dust grains and the resulting impact features in both collector materials is discussed. © 2009 American Institute of Physics.