Collision of a chondrule with matrix: Relation between static strength of matrix and impact pressure

Chondrites are one of the major groups of meteorites. They consist of spherical objects called chondrules, which are typically (sub-)millimeter-sized, and fine-grained matrix between the chondrules. There exists a variety of models on the formation of chondrules, most of which have in common that chondrules were formed at some local place in the protoplanetary disk and later incorporated into the planetesimals which then formed the chondrite parent bodies. However, it has not yet been fully investigated how and under which conditions chondrules coalesce with the matrix. In this experimental study, we assume that chondrules and matrix were formed at different places in the protoplanetary disk and subsequently collided with each other. For this, we investigated the relation between the bulk strength of agglomerates and the impact pressure, and the threshold velocity for a chondrule to be embedded into the matrix. We performed collision experiments using three different accelerators to achieve collision velocity from 0.2 to 300 m s−1. We also carried out static strength measurements for silica agglomerates which were used as targets to investigate their mechanical properties, using a compressive-strength testing machine. Finally, we measured the elastic limits of the dust agglomerate from their compression (pressure-displacement) curves. We found three types of collision outcomes: bouncing, surface sticking and intrusion of the chondrule-analog projectile. Comparing the compressive strength of the target with the impact pressure, we found that intrusion occurs when the strength of the target is smaller than the impact pressure. On the other hand, bouncing occurs when the strength of the target is larger than the impact pressure. The minimum intrusion velocities of chondrules for targets with 50% and 75% porosity were determined to be 46 and 3 m s−1, respectively.