A novel production strategy for high-porosity simulants of Ryugu surface boulders

This study presents a strategy to produce artificial rocks, or simulants, designed to replicate boulders observed on the surface of asteroid Ryugu. The simulants are composed of a dust mixture with bulk composition and grain size distribution based on the analysis of particles returned from Ryugu by the Hayabusa2 mission. Two production methods, freeze-drying and dry-compression, were established to generate simulants with porosities between 45% and 80%. Five key parameters were used to characterise the simulants and to compare them with Ryugu particles: the bulk composition of the dust mixture, the size and shape distribution of the individual components, the simulant microstructure, i.e. the internal distribution of material and void spaces, and the interaction between the grains within the simulant. These parameters were assessed using scanning electron microscopy, laser diffraction, helium gas pycnometry, and micro-tomographic analysis. Even though some discrepancies in composition and grain size distribution remain, these can be addressed in future updates of the simulant dust mixture. It was generally found that freeze-dried simulants capture the microstructure and grain interactions of Ryugu particles better than the dry-compressed simulants. In a next step, thermal and mechanical properties of the simulants will be measured to support the interpretation of remote sensing observations of Ryugu’s surface.