Regolith particles diameter for different filling factors ϕ. The horizontal dashed black line corresponds to the nominal estimate of K of 0.012 W m⁻¹ K⁻¹, the dashed red line to the upper limit of 0.1 W m⁻¹ K⁻¹, and the colored curves depict the dependency of the thermal conductivity as a function of the regolith particle diameter. The conductivity of solid material was assumed to be λ_solid = 1.5 W m⁻¹ K⁻¹ for the plot on the left, and λ_solid = 4 W m⁻¹ K⁻¹ for the plot on the right. The intersections between the horizontal dashed lines and the curves, indicated by black circles, correspond to the estimated grain size.