Heat transfer in granular media with weakly interacting particles

We study the heat transfer in weakly interacting particle systems in vacuum. The particles have surface roughness with self-affine fractal properties, as expected for mineral particles produced by fracture, e.g., by crunching brittle materials in a mortar. We show that the propagating electromagnetic (EM) waves and the evanescent EM-waves, which occur outside of all solids, give the dominant heat transfer for large and small particles, respectively, while the phononic contribution from the area of real contact is negligible. As an application we discuss the heat transfer in rubble pile asteroids.