Numerical simulations of asteroids modelled as gravitational aggregates with cohesion

Evidence is mounting that asteroids larger than a few hundred metres in diameter are gravitational aggregates of smaller, cohesive pieces. For example, images of 25143 Itokawa show a boulder-strewn surface reminiscent of what might be expected following gravitational reaccumulation of material ejected from a catastrophic impact into a larger body. We have developed a new numerical approach to modelling gravitational aggregates that includes for the first time several prescriptions for variable material strength/cohesion while preserving the desirable features of fast and accurate computation from our prior methods. The new model can be used to construct non-idealized rubble piles made up of irregular, competent pieces, or to preserve shape and spin information of reaccumulated bodies in high-resolution simulations of asteroid family formation, by allowing fragments to stick on contact (and optionally bounce or cause further fragmentation, depending on user-selectable parameters). We detail the numerical method, which involves solving the rigid-body equations of motion and handling non-central/off-axis impacts, and present simulations of collisional and rotational disruption of asteroids as illustrative examples. This work is part of an ongoing effort to improve the realism and applicability of numerical simulations to the collisional and dynamical evolution of asteroids and other small solar system bodies.