Accretion in the Main Asteroid belt

The present day Main Asteroid belt (MAB), located between the orbits of Mars and Jupiter, has a total estimated mass of about 10,000 times smaller than that of the Earth. Such a low mass compared to that of the neighboring planets led to two conclusions. (i) The MAB was never massive, or maybe it was even born empty. In this case, the MAB mass would result from a small fraction of implanted objects coming from the terrestrial and giant planet regions after or during these planets’ formation. (ii) The MAB original mass was as high as some Earth masses and later depleted by dynamical mechanisms that invoke giant planet migration and orbital instability. The current MAB population is also known to be composed by roughly one million objects larger than D = 1 km in size. Yet, from those, only three have D > 500 km (Pallas, Vesta, and Ceres). Regardless the possible origin of these three objects, the primordial mass of the MAB cannot be such that accretion would lead to too many objects with D > 500 km. If that was the case, it is very likely that some would survive solar system evolution and would be observed at present days (which is not the case). Therefore, in this study, we aim to better constraint the original mass of the MAB by following the accretion of planetesimals in that region. Our results will report on the number of objects with D > 500 km formed in the regions known as inner, center, and outer main belt, as a function of the MAB primordial mass, initial planetesimal size-frequency distribution, and accretion time.