Kenkmann, and 34 co-authors, presented in 2018 the major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta.
In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise: 1) projectile–target interaction, 2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, 3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, 4) in situ target damage, 5) ejecta dynamics, and 6) geophysical survey of experimental craters.
The authors concluded that:
1. Insights in the energy budget of selected impact experiments show that target fragmentation and comminution consumes <5% of the impact energy. Melting and vaporization of projectiles consumes 4– 5% at 5.3 km s-1 impact velocity.
2. Significant inter-element fractionation occurs during mixing of projectile and target melts.
3. The degree of fractionation is controlled by the lithophile or siderophile character of the respective elements.
4. Target porosity exponentially reduces crater volume and cratering efficiency while it increases crater depth relative to nonporous rocks, and also flattens ejection angles. The combined approach of numerical modeling and cratering experiments lead to improved scaling laws and a better understanding of porosity and strength on crater size scaling.
5. Higher degrees of water saturation in sandstone targets yield an increase in total ejecta mass, up to 400% higher mean ejection velocity, and steeper ejecta cone angles, with respect to dry targets.
6. A new pressure calibration of shock metamorphic features in porous rocks and low shock pressures was established. Localized shock pressure amplification as a consequence of pore space collapse was quantified by mesoscale modeling to be a factor of 4, if not more.
7. For the first time stishovite was experimentally produced in low-pressure shock experiments and this work indicated ultrafast crystallization from silica melt at high pressure.
8. Nondestructive geophysical analysis of targets using ultrasound tomography shows that the damage zones beneath craters is wider than indicated by microstructural inspection at the SEM scale.
9. A novel mesoscale numerical model considers grains of various sizes and shapes and allows for shear localization at grain boundaries
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