An alternative model for the formation of the asteroids

Abstract

The growth and orbital evolution of a swarm of ∼10 26-g “planetary embryos,” originally distributed throughout both the terrestrial planet and the asteroidal regions has been simulated using a Monte Carlo technique previously used by the author to study the formation of the terrestrial planets alone. The effects of the giant planets, primarily Jupiter, are simply assumed to be those operative at present: chaotic acceleration in resonance regions and gravitational ejection of objects by encounters with Jupiter at aphelia ≳4.75 AU. It is found that the asteroidal embryos are very effective in scattering one another into resonance regions. The resulting orbital evolution clears the asteroid belt of embryos in about half of the simulations. Embryos accumulate in the terrestrial planet region to form a stochastically determined variety of planetary configurations that are similar in total mass, specific energy, specific angular momentum, planetary size, and orbital elements to our Solar System. The small quantity of material remaining in the asteroid region has a velocity distribution very much like that of the observed asteroids. It is concluded that this model, although certainly imperfect, represents a viable alternative to models in which the initial asteroidal population is limited to bodies the size of the present asteroids.