Thermal conductivity as a function of regolith particle radius for Gaspra (top) and Ida (bottom). Dashed lines show thermal conductivities derived from the mean thermal inertia and heliocentric distance. Solid curves represent the vacuum-regolith model using silicate-rich meteorite analogs (B. Gundlach & J. Blum 2013). Black crosses indicate the inferred grain sizes: ﹩{1148}_{-352}^{+495}﹩μm for Gaspra and ﹩{679}_{-178}^{+195}﹩ μm for Ida.