Interior structure and surface properties of NEOs: What is known and what should be understood to mitigate potential impacts Original Research Article

Indirect information about interior structure and surface properties of near-Earth asteroids and cometary nuclei is provided by observations, together with numerical and laboratory simulations. Such studies already indicate a huge diversity amongst the whole population, in bulk density (from 0.2 to 3 g cm−3), in macro-porosity (tentatively from 18% to 60%), and thus in structure (small monolithic objects, bigger fractured objects or gravitational aggregates, as well as porous and nevertheless robust objects formed of cohesive material). The surface physical properties of asteroids are consistent with the existence of regolithic layers, built up of irregular particles with a size greater than the wavelength, and corresponding to a porosity higher than that of the whole object. A precise knowledge of the interior structure and of the regolith properties – of major importance to assess the consequences of an impact and develop efficient mitigation strategies – can only be provided by in situ rendezvous missions, aimed at significantly different objects, representative of different categories of physical properties.