Observations of Complex Regolith Behavior in a Vacuum Microgravity Experiment

Abstract:

Images from Bennu and Ryugu have shown surfaces with particle size distributions vastly different to those previously observed on other small bodies such as Itokawa, Eros, or even the Moon. It is evident that there are particle size-dependent sorting mechanisms at work that may vary between planetary bodies. Gravity is a significant factor in a number of these processes, for instance, it influences the sizes of particles that are retained due to impact and ejection. One method of redistribution that likely influences surface particle size expression is through vibrations, which may result in both particle size and gravity-dependent sorting. Previous and ongoing research with a set of experiments on the International Space Station is exploring these vibration-dependent interactions in a vacuum, microgravity environment with a range of regolith simulant materials. Through video observations, we retain a record of particle motion at the “surface” of the experiment and can tie this with stratification and modified size distributions over time. We will present observations of the material behavior, comparing the behaviors of the jagged glass materials with a discrete size distribution and a higher-fidelity regolith simulant with a more complex size distribution, including a greater percentage of fines. These behaviors will be tied to specific acceleration/vibration profiles that the regolith experiences. We observe significant differences in the behavior of the two regolith types, but also find certain disturbances, or including stronger acceleration events, that are evident in both experiments.