INVESTIGATING CRATER EJECTA EMPLACEMENT IN THE LABORATORY: PRELIMINARY SCALING RESULTS

Impact cratering is the most-widespread exogenic surface process that modifies surfaces of solid Solar System worlds. On worlds with sufficient gravity, the ejecta excavated by impacts are largely retained and re-impact the surface. As such, these ejecta contribute to geomorphic change via the process of ballistic sedimentation. Our laboratory investigation of the ejecta-emplacement process aims to understand the dynamics of ejecta deposition, flow, and mixing with in situ regolith, and further our knowledge of the production of observed geomorphology and stratigraphy. The over-arching purpose is to aid interpretation of, e.g., lunar sample provenance, remotely-sensed spectral datasets (Li & Mustard, 2000), and ejecta contributions to crater rim uplift (Sharpton, 2014).

Our principal experimental apparatus is the ejecta emplacement catapult (Barnouin et al., 2012), which flings ejecta simulant (pea gravel) onto various targets. A high speed camera (1200 fps) records the ejecta’s velocity as well as its subsequent deposition. A laser topographic profiler records the resulting ejecta deposit topography. Alternatively, removable catchment cells allow the ejecta to be massed to record the deposit’s mass distribution before it has a chance to flow. The combination of these data provide estimates of the initial momentum and energy of an amalgam of ejecta simulant before interacting with a target surface and thus the potential for geomorphic change. Laboratory-determined crater scaling rules are used to relate the velocity and mass of the in-flight and depoited ejecta simulant to the velocity and mass of natural ejecta from craters. Combining these results to the crater scaling rules for ejecta provides a new quantitative means to assess the effects of ejecta emplacement at broad planetary scales by various sections of an ejecta curtain, which can be compared to past models of ballistic sedimentation via ejecta emplacement.