Predicted strength, microporosity, thermal conductivity and grain density of Ryugu rock samples

Abstract

In this presentation, we summarize the findings and interpretations of the physical and thermophysical properties of C-type asteroid 162173 Ryugu obtained from Hayabusa2 remote sensing as well as from MASCOT radiometer (MARA) data. For a typical rock on Ryugu's surface, we find a thermal inertia of 295 ± 18 Jm-2K-1s-1/2 (Hamm+ 2020), a microporosity of 50 ± 3% (Grott+ 2020, Hamm+, 2020), and assuming a CM chondrite composition and thus an inferred specific heat capacity of cp=890 J/kg/K ( ± 10%, at an average temperature of 277K), we estimate a thermal conductivity of 0.069 ± 0.012 J/m/K at ~277 K. These estimates are based on MARA surface brightness temperature measurements of an arguably (Biele et al, 2019) dust-free boulder at MASCOT's landing site obtained over a full diurnal cycle. Those values are consistent with the TIR instrument's global findings (Okada+ 2020). The very high deduced microporosity lets us reasonably estimate the tensile strength of those abundant "cauliflower rocks" (Jaumann+ 2019), ~200-280 kPa (Grott+, 2019).