Collision and gravitational reaccumulation: Possible formation mechanism of the asteroid Itokawa

Aims. We investigate the possibility that the observed sea-otter shape of the asteroid Itokawa, associated with the presence of big boulders on its surface, originates from the reaccumulation process that may have formed this asteroid, assuming that it consists of reaccumulated fragments from a catastrophically disrupted parent body. Methods. We computed the gravitational phase of an asteroid disruption, during which fragments can reaccumulate and form aggregates, using a version of the N-body code pkdgrav that includes a model of rigid aggregates. This new model allows the formation of non-idealized rubble piles as a result of reaccumulation that are made up of irregular, competent pieces. Shape and spin information of reaccumulated bodies are thus preserved by allowing fragments to stick on contact (and optionally bounce or cause further fragmentation, depending on user-selectable parameters), instead of merging into growing spheres. Results. We find that the reaccumulation process of an asteroid disruption can produce aggregates whose form is similar to that of Itokawa, and can lead to the deposit of big boulders on the surface, as observed on Itokawa.