COLLISIONAL EVOLUTION OF TROJAN ASTEROIDS

We model the collisional evolution of Trojan asteroids using a numeric al code which combines recent calculations of the intrinsic collision probabilities and impact speeds in the Trojan swarms (Marzari et al. 1 996) with our current understanding of the outcomes of high-velocity c ollisions between asteroid-sized bodies. Using plausible collision par ameters and energy scaling of impact strength with size, we obtain a g ood match to the present Trojan population, as inferred by Shoemaker e t al. (1989). The steep slope of the current Trojan size distribution at diameters larger than about 50-100 km is essentially unaltered by t he collisional process and must reflect the formative processes of the se bodies. At smaller sizes, collisions have produced a power law size distribution having a slope characteristic of collisionally relaxed p opulations. Hence, we cannot distinguish whether the small-size end of the distribution was formed before or after the disruptive collisiona l regime characteristic of the present Trojan environment was establis hed, The formation of prominent dynamical families in the Trojan swarm s is a natural outcome of the collisional process; their number may al low us to constrain the degree of collisional evolution that has occur red in the Trojans, Finally, we find that Trojan collisional debris es caping from the libration regions and ending up into cometary orbits c ould supply approximate to 10% of the current population of short-peri od comets and Centaur asteroids. Whether this occurs depends on the dy namical lifetime of such bodies and whether they contain enough volati les to become active comets. (C) 1997 Academic Press