Simplified Simulated Materials of Asteroid Ryugu for Spacecraft Operations and Scientific Evaluations

There are growing demands for simulated asteroid materials (simulants) due to the increasing number of asteroid missions and interest in space resources. While a simulant should have a high fidelity to a target body for general scientific and engineering purposes, a simplified and purpose-specialized simulant is also useful for specific purposes, which often arise during actual space missions. In the mission phase of the Hayabusa2 spacecraft, which is a sample return mission from a C-type asteroid, Ryugu, we developed simplified simulants based on terrestrial observations of the asteroid. These observations indicate that Ryugu is similar to carbonaceous meteorites, especially to CM or CI chondrite. Due largely to the limited time available to produce the simulant, we decided to keep the constituent as simple as possible. Because the main constituent mineral that comprises carbonaceous chondrites is phyllosilicate, we used serpentine (mostly lizardite) as the base material for the simulant. By adjusting the abundance of the carbon suspension, we controlled the reflectance in the wavelength region of the visible to near infrared. As a result, we found that the characteristics of the simplified Ryugu simulant developed by this study simulate relatively closely the materials of carbonaceous meteorites in terms of density and spectral characteristics. The simplified simulant was especially useful for evaluating the initial data obtained by the spacecraft and the sampling device before obtaining actual samples.