EXPERIMENTAL IMPACTS INTO SLOPED TARGETS – A FIRST LOOK

Impact cratering has been and continues to be the dominant macroscopic surface process on the majority of solid bodies in the solar system. Impacts form craters that act as subsurface probes, excavating subsurface material and depositing it outside of the crater, generating and mixing the regolith, and launching future meteorites. Current knowledge of the excavation and modification of impact craters from experiments and numerical models is limited primarily to cases of horizontal targets. Thus, existing experimentation and numerical modeling provide only first-order guidance when considering the effects of impact in more realistic planetary environments with actual topography.

We are taking the next logical step in experimental impact-cratering studies by investigating the effects of regional target topography on the impact process. We have performed a suite of impact-cratering experiments in the Experimental Impact Laboratory at NASA Johnson Space Center, comparing impacts into sand targets with horizontal surfaces to those with a surface slope of 20°. Ejecta leaving the target was imaged with the Ejection-Velocity Measurement System (EVMS), which projects a vertical plane of laser light through the impact point. This laser plane is strobed at a known rate while a digital camera images the event, which allows individual ejecta particles to be tracked along their ballistic trajectories to determine the particle’s ejection position, speed, and angle. A 3D laser scanner was used to record the original surface topography of the target and the final crater shapes and dimensions after impact.

Here we present our initial results comparing ejecta kinematics for an impact into a sloped target and a near-identical impact into a horizontal one. Future experimental work will examine a range of different slopes in all directions around the impact point (upslope through downslope). These results will be used to adapt and modify existing crater-scaling relationships to describe the behavior of more complex target surfaces.