Abstract
Context. Impacts on small-body surfaces can occur naturally during cratering events or even strategically during carefully planned impact experiments, sampling maneuvers, and landing attempts. A proper interpretation of impact dynamics allows for a better understanding of the physical properties and the dynamical process of their regolith-covered surfaces and their general evolution. Aims. This work aims to first validate low-velocity, low-gravity impact simulations against experimental results, and then to discuss the observed collision behaviors in terms of a popular phenomenological collision model and a commonly referenced scaling relationship. Methods. We performed simulations using the soft-sphere discrete element method and two different codes, Chrono and pkdgrav. The simulations consist of a 10-cm-diameter spherical projectile impacting a bed of approximately 1-cm-diameter glass beads at collision velocities up to 1 m s−1. The impact simulations and experiments were conducted under terrestrial and low-gravity conditions, and the experimental results were used to calibrate the simulation parameters. Results. Both Chrono and pkdgrav succeed in replicating the terrestrial gravity impact experiments with high and comparable computational performance, allowing us to simulate impacts in other gravity conditions with confidence. Low-gravity impact simulations with Chrono show that the penetration depth and collision duration both increase when the gravity level decreases. However, the presented collision model and scaling relationship fail to describe the projectile’s behavior over the full range of impact cases. Conclusions. The impact simulations reveal that the penetration depth is a more reliable metric than the peak acceleration for assessing collision behavior in a coarse-grained material. This observation is important to consider when analyzing lander-regolith interactions using the accelerometer data from small-body missions. The objective of future work will be to determine the correct form and applicability of the cited collision models for different impact velocity and gravity regimes.
Highlights
After decades of study, scientists still struggle to describe the complex process that occurs when an object is dropped onto a bed of granular material
Impact dynamics have been investigated extensively using laboratory experiments in order to explain how collision behavior scales with factors such as the projectile size, impact velocity, and target surface material (Omidvar et al 2014; Katsuragi 2016)
We identify the simulation parameters that generate the best match between the numerical and experimental results, and we compare the computational performances of the two codes
Summary
Scientists still struggle to describe the complex process that occurs when an object is dropped onto a bed of granular material. A particular variable of interest, though one that is much more difficult to study, is gravity. Understanding the role that gravity plays in granular collisions is essential to optimize our gain from future planetary exploration missions. Accurate collision models can help us design systems to land and operate on asteroid surfaces, as well as improve our ability to deduce a body’s surface material properties from the size and shape of its craters. The response of planetary surfaces to impacts is highly important for understanding the bodies’ geophysical evolution, and for providing accurate estimates of surface ages (Marchi et al 2015)
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