Abstract
Recent observations suggest that many of small asteroids (100m $<$ R $<$ 100km) may be gravitational aggregates. Since collisions change the spin of these asteroids, their spin distribution would provide useful information about their origin and collisional evolution. However, little has been studied on the efficiency of angular momentum transfer during collision between rubble pile objects. Using N-body method to simulate impact event between rubble pile objects, we have examined transfer of angular momentum to a target (or the largest remnant if the impact is disruptive) from the orbital angular momentum of an impactor. We performed a large number of simulations with various values of parameters, such as the mass ratio of colliding objects, impact parameter, impact speed, and the degree of energy dissipation at impact. Our simulations show low angular momentum transfer efficiency at disruptive collisions, and we found a clear relationship between the angular momentum transfer efficiency and the degree of disruption, and this relationship appears not to depend on the dissipation parameter. We will discuss implications of our results for the spin evolution of asteroids.
