The Physics of Protoplanetesimal Dust Agglomerates. I. Mechanical Properties and Relations to Primitive Bodies in the Solar System

We present laboratory experiments on the formation of macroscopic dust aggregates. The centimeter-sized highly porous bodies are produced by random ballistic deposition from individual micrometer-sized dust particles. We find packing densities between 0.07 and 0.15 for uncompressed samples, dependent on the shape and size distribution of the constituent dust grains. Impacts into these bodies are simulated by uniaxial compression experiments. We find that the maximum compression, equivalent to the highest protoplanetary impact velocities of ~50 m s^-1, increases the packing density to 0.20-0.33. Tensile strength measurements with our laboratory samples yield values in the range 200-1100 Pa for slightly compressed samples. We review packing densities and tensile strengths found for primitive solar system bodies, e.g., for comets, primitive meteorites, and meteoroids. We find a consistency between packing densities and tensile strengths of our laboratory samples with those from cometary origin.