Transient cavity evolution and morphology after the impact of a spherical gel drop on a deep gel pool

Impact craters appear in many natural and industrial processes. Their dynamics are widely studied using Newtonian fluids or granular media. However, in some processes the yield strength of the impactor and the target is important. In this work, motivated by planetary impacts, we present results from an experimental study where both the impactor and the target are Carbopol gel. We use a high-speed camera to record the falling of the impactor, which is dyed to be distinguishable from the pool material after impact, and a second high-speed camera to record the cavity evolution through a transparent tank. The experimental parameters of our lab impacts are in the lowest energy limit of planetary impacts and surface tension effects are negligible. We perform analysis of the transient morphology of the cavity and find dependence on the material yield strength. Also, whereas for high-Reynolds-number craters in Newtonian fluids there is near perfect conversion of the impactor kinetic energy into the potential energy of the maximum transient cavity, here we find that some of the energy is expended to yield the material. Before reaching a final depth in the pool, the impactor material oscillates vertically in a damped oscillation with period that depends on material elasticity.