Discussion: Collisional History of Asteroids

Abstract

We found that low-velocity and non-destructive impacts produce various shapes including extremely flat shapes, while high-velocity and destructive impacts produce spherical and bilobed shapes but they do not produce flat shapes. The impact velocity is strongly affected by the environments of planetary systems such as the existence of gas components or giant planets. Low-velocity impacts are realized in the primordial environment, while high-velocity impacts are realized in the present environment. Thus we may connect shapes of asteroids to the environments or era when asteroids were formed. In this chapter, we discuss the connection between shapes of asteroids and formation era. We also investigate information of actual asteroids including those shapes obtained from several databases, and we find that many flat asteroids are not included in any asteroid families. Both the results of our simulations and the information of actual asteroids suggest that flat shapes of large asteroids are likely to be formed in the primordial environment and they keep their flat shapes until today.