Preliminary laboratory investigations of ejecta emplacement dynamics and morphology with planetary applications

Abstract

The preponderance of impact craters and the associated crater ejecta facies are leading agents of geomorphic change across the Solar System. Interpretation of planetary landscape evolution, sample provenance, and regolith gardening all benefit from a thorough understanding of ejecta emplacement dynamics. Constraining the type and range of these dynamics has eluded experimentation even as the effects of primary impacts have become well-constrained from experiments and numerical simulations and have been shown to follow power law scaling relationships. To address the knowledge gap surrounding granular ejecta emplacement, we built and characterized a novel ejecta emplacement catapult and showed it to accurately reproduce the ejecta mass and velocity profiles predicted for in-flight natural ejecta curtains. Based on this dynamic similarity to larger, natural systems, we proceeded with a preliminary exploratory suite of experiments to constrain runout and erosion efficiencies of flowing ejecta. Our quantitative results at low speeds may suggest a new set of scaling relationships for erosion via ballistic ejecta versus crater formation and erosion from hypervelocity clustered projectiles. Our results also show significant ejecta runout efficiencies of ∼1–2 (only slightly below the efficiencies of terrestrial debris flows 12 decades more voluminous) with important erosive efficiencies of ∼2–4%. Our qualitative results reveal a stochastic and heterogeneous system: ejecta “saltation” and implantation, and regolith exhumation, erosion, and shearing. Together with the initial results showing ejecta emplacement to be violently dynamic, the development of this new laboratory technique will enable more detailed studies to better inform interpretations of sample provenance, ejecta stratigraphy, and geochemical boundaries.