Laboratory Study of Compaction of Granular Bodies due to Collisions in Interplanetary Space

Abstract

Small bodies in the Solar System are composed of granular materials such as dust and collisional debris. They have experienced accumulation and destruction due to collision. The most porous small bodies at present have porosity higher than 80% and it could have been even higher in the earlier stage. Granular layer at the impact point is compacted due to compression. On the other hand, porosity of the location far from the impact point can also change by fluidization due to collision-induced vibration. In this study, uniaxial pressure was applied to the granular layers of different constituent particles and the change of porosity was investigated. As a result, it was shown that there was a pressure range where the initial porosity was kept almost constant, and above that, the porosity decreased with increasing pressure. This threshold was taken as the “yield strength” of the granule layer, and the average force acting between the individual particles was estimated. This force took a value between the theoretical values of rolling frictional force and sliding frictional force acting between particles. In addition, it was shown that particles with smaller sliding friction force tended to be compressed more easily.