Laboratory impacts into dry and wet sandstone with and without an overlying water layer: Implications for scaling laws and projectile survivability

Abstract

Abstract-Scaling laws describing crater dimensions are defined in terms of projectile velocity and mass, densities of the materials involved, strength of the target, and the local gravity. Here, the additional importance of target porosity and saturation, and an overlying water layer, are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s −1 into a) an initially uncharacterized sandstone (porosity ~17%) and b) Coconino Sandstone (porosity ~23%). The higher-porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower-porosity dry sandstone. Furthermore, for both porosities, a greater volume of material is excavated from a wet target than a dry target (by 27-30%). Comparison of our results with Pi-scaling (dimensionless ratios of key parameters characterizing cratering data over a range of scales) suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a π v versus π 3 plot (π v gives cratering efficiency and π 3 the influence of target strength). An overlying water layer results in a reduction of crater dimensions, with larger craters produced in the saturated targets compared to unsaturated targets. A water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets. Previous experimental studies have shown that this ratio varies between 10 and 20 (Gault and Sonett 1982). In our experiments ~25% of the original projectile mass survives the impact.

The effect of the oceans on the terrestrial crater size‐frequency distribution: Insight from numerical modeling

“…The main reason for this is probably the greater difference in density between the impactor and water in their experiments (they used stainless steel impactors), although the experiments also differ considerably from our model simulations in terms of projectile size, projectile velocity, and the target property controlling crater growth in the rock (strength in the case of the experiments; gravity in the case of the models). We find that Equation 2 fits the data of Baldwin et al (2007) reasonably well (for R < 6) using = 0.28, suitable for solid rock in the strength regime (see Melosh 1989, p. 119, Eq. 7.7.13 [note that this equation is wrong by a factor of −1]), and ρ i = 7800 kg m −3 .…”

“…A final regime-the deep water regime-is observed in our models for R > 8; in this case, the water layer completely dissipates the energy of the impactor, and no trace of the impact is observable on the seafloor. Laboratory-scale impact experiments (Gault and Sonnett 1982;Baldwin et al 2007) suggest that the deep-water regime may not begin until R ∼ 10.…”

“…Artemieva and Shuvalov (2002) also found from their numerical models that for R > 4, a submarine crater is almost nonexistent (for an impactor 1 km in diameter with an impact velocity of 20 km s −1 ); however, the marine-impact models of Wünnemann and Lange (2002) did show significant disturbance of the seafloor for R = 5 (using the same impactor size and velocity). Laboratory-scale impact experiments (Gault and Sonnett 1982;Baldwin et al 2007) provide further quantitative analysis of the effect of water layer thickness on crater size, albeit at a much smaller scale and lower velocity than typical marine craters. Results from these experiments suggest that craters may form in the target beneath water of depths up to 10-20 times the diameter of the impactor (R = 10-20).…”

Comment on "Determining Chondritic Impactor Size from the Marine Osmium Isotope Record"

“…Impacts into deep water greatly increase the chance of survivability of the projectile (4), with up to 25% of the projectile failing to be vaporized on impact. For an impactor of the same size and velocity, more projectile material survives if the impact angle is oblique than if it is subvertical (4,5). Modeling also shows that, as impact velocity increases and impact angle decreases, an increasing fraction of the projectile leaves Earth at greater than escape velocity (6, 7).…”

“…Simulations of impacts using laboratory experiments and numerical models indicate that the fate of the projectile is dependent on impact target properties, velocity, and angle, as well as projectile size (4,5). Impacts into deep water greatly increase the chance of survivability of the projectile (4), with up to 25% of the projectile failing to be vaporized on impact.…”