Density and composition of interplanetary dust particles

Residual meteoritic material has been detected on the surface of crater interiors on lunar samples 60315,29 and 65315,68. Iron-nickel nicrometeoroid residues are present in the form of metallic spherules embedded in or attached to the crater glass-linings; stony-iron meteorite residual material is homogeneously mixed with the glass-linings. Crater simulation experiments show the dependence of crater diameter to depth ratio or projectile density. On the other hand, the projectile velocities exceeding 4 km/s have no measurable influence on the D/T ratios of microcraters. As a result, diameter-to-depth measurements on lunar microcraters yield three groups of micrometeorites in the size range between 1 μm and 1 mm: iron-nickel, stony-iron and low-density particles. The measured D/T values correspond directly to the kind of determined projectile residues: craters showing residues of iron-nickel meteorites have ratios of D/T=1.3-1.4 and craters with stony-iron residues have ratios of D/T=1.9-2.1. Craters with diameters < approximately 30 μm seem to have been formed predominantly by iron-nickel micrometeorites, whereas craters with diameters > approximately 80 μm predominantly by stony meteorites. (Auth.)