Collisional evolution of Edgeworth-Kuiper Belt objects

The Edgeworth-Kuiper Belt contains a population of objects approximate to 10(3) times that of the main asteroid belt, spread over a volume approximate to 10(3) larger and with relative speeds approximate to 10 times lower, As for the asteroids, the size distribution of Edgeworth-Kuiper Belt objects has been modified by mutual impacts over Solar System history. We have modeled this collisional evolution process using a numerical code developed originally to study asteroid collisional evolution but modified to reflect collision rates in the Edgeworth-Kuiper Belt. Our numerical simulations show that collisional evolution is substantial in the inner part of the Edgeworth-Kuiper Belt, but its intensity decreases with increasing distance from the Sun. In the inner belt, objects with diameters D > 50-100 km are not depleted by disruptive collisions; hence they reflect the original (formative) population (many of them, however, may have been converted into ''rubble piles''). On the other hand, smaller objects are mostly multigenerational fragments, although the original population must have contained a significant number of bodies down to at least a few tens of kilometers in size in order to initiate a collisional cascade. About 10 fragments, 1-10 km in size, are produced per year in the inner Edgeworth-Kuiper Belt, with a few percent of them inserted into chaotic resonant orbits. This is in rough agreement with the required influx rate of Jupiter-family comets. Both collisions and dynamical instabilities associated with resonances are processes that can inject comets into the ''escape hatches,'' but our results indicate that most comets coming from the Edgeworth-Kuiper Belt would be fragments from larger parent bodies, rather than primitive planetesimals. However, this does not apply to Chiron-sized (D > 100 km) objects, which must be primordial and delivered to the outer Solar System by either dynamical processes or nondisruptive collisions. (C) 1997 Academic Press