Impact Jetting of Geological Materials

To understand jetting of earth materials, gabbro slabs (5 mm thick) were accelerated to 1.5-2 km sec^(-1) and impacted gabbro (5-10 mm thick), novaculite (10 mm thick), and porous sandstone (12 mm thick) targets at inclination angles of 30°-60°. The ejecta were collected using a catcher box filled with styrofoam and the particles are extracted using chloroform. Jetting angles are determined by the relative positions of the target and the crater produced by the ejecta. The mass of the ejected particles per unit area (∼50 mg cm^(-2)) of the impactor remains almost independent of the impact velocity, inclination angle, thickness of the target and sample mineralogy, and density. Hydrodynamic models are used to calculate the jetting mass, angle, and velocity. Theoretical models predict ∼6 times more ejecta than the experimentally measured as the inclination angle increases. X-ray diffraction of the recovered ejecta shows that it is still in crystalline form, which agrees with thermodynamic calculations. Because the experimental results indicate that the theoretical jetting model for thin metal plates provides a poor description of the experiments, the application of metal plate theory to planet-sized objects appears to be questionable.