[PPS02-P07] Thermal conductivity of lunar regolith simulant and implication to grain size estimate using thermal inertia
As a result, we found that JSC-1A has similar solid and radiative conductivities to Apollo regolith samples, and it can be used to simulate the thermal conductivity of the lunar top surface. We also confirmed that a series of the experimental data for JSC-1A can be calibrated by an analytical thermal conductivity model we developed (Sakatani et al., 2017, AIP Adv.). Moreover, the thermal conductivity of sieved samples with grain size about 100 μm had a similar conductivity to the original JSC-1A. The original sample has a volumetric median grain size about 100 μm, so that it is inferred that the thermal property of soils with a broad grain size distribution can be modeled as mono-sized grains with a volumetric median. In other words, a grain size estimated from the thermal observation data is a volumetric median size. Comparison with the experimental data for size-sorted spherical glass beads indicated that the irregular shapes of the natural samples reduce the conductivities by a few ten percent. We are planning to apply the thermal conductivity model calibrated in this study to the Hayabusa2 Thermal Infrared Imager data of asteroid Ryugu so as to determine the spatial distribution of the grain size of surface materials on the asteroid.