Regolith grain size and cohesive strength of near-Earth Asteroid (29075) 1950 DA

Abstract

Due to its fast rotation period of 2.12h, about half of the surface of near-Earth Asteroid (29075) 1950 DA experiences negative (i.e., outward directed) acceleration levels (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174–176). Thus, cohesion of the surface material is mandatory to prevent rotational breakup of the asteroid. Rozitis et al. (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174–176) concluded that a grain size of ∼6cm or lower is needed to explain the required cohesive strength of 64-20+12Pa. Here, we present another approach to determine the grain size of near-Earth Asteroid (29075) 1950 DA by using the thermal inertia value from Rozitis et al. (Rozitis, B., Maclennan, E., Emery, J.P. [2014]. Nature 512, 174–176) and a model of the heat conductivity of the surface regolith (Gundlach, B., Blum, J. [2013]. Icarus 223, 479–492). This method yields a mean particle radius ranging from 32μm to 117μm. The derived grain sizes are then used to infer the cohesive strength of the surface material of Asteroid (29075) 1950 DA (ranging from 24Pa to 88Pa), by using laboratory measurements of the tensile strength of powders.