When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters. Inspired by this similarity, we integrate the physical insight from planetary sciences, the liquid marble model from fluid mechanics, and the concept of jamming transition from granular physics into a simple theoretical framework that quantitatively describes all of the main features of liquid-drop imprints in granular media. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes.liquid impacts | granular impact cratering | jamming | liquid marble G ranular impact cratering by liquid drops is likely familiar to all of us who have watched raindrops splashing in a backyard or on a beach. It is directly relevant to many important natural, agricultural, and industrial processes such as soil erosion (1, 2), drip irrigation (3), dispersion of microorganisms in soil (4), and spray-coating of particles and powders. The vestige of raindrop imprints in fossilized granular media has even been used to infer air density on Earth 2.7 billion years ago (5). Hence, understanding the dynamics of liquid-drop impacts on granular media and predicting the morphology of resulting impact craters are of great importance for a wide range of basic research and practical applications.Directly related to two long-standing problems in fluid and granular physics research, i.e., drop impact on solid/liquid surfaces (6-9) and granular impact cratering by solid spheres (10-16), liquid-drop impact on granular surfaces is surely more complicated. Although several recent experiments have been attempted to investigate the morphology of liquid-drop impact craters (17-21), a coherent picture for describing various features of the impact craters is still lacking. Even for the most straightforward impact-energy (E) dependence of the size of liquid-drop impact craters, the results remain controversial and incomplete (17,19,20). Katsuragi (17) and Delon et al. (19) reported that the diameter of liquid-drop impact craters D c scales as the 1/4 power of the Weber number of liquid drops, which yields D c ∼ E 1=4 , quantitatively similar to the energy scaling for low-speed solid-sphere impact cratering (10, 11). However, because the energy balance of liquid-drop impacts is different from that of solid...
