  Containing only a few percent the mass of the moon, the current asteroid belt
is around three to four orders of magnitude smaller that its primordial mass
inferred from disk models. Yet dynamical studies have shown that the asteroid
belt could not have been depleted by more than about an order of magnitude over
the past ~4 Gyr. The remainder of the mass loss must have taken place during an
earlier phase of the solar system's evolution. An orbital instability in the
outer solar system occurring during the process of terrestrial planet formation
can reproduce the broad characteristics of the inner solar system. Here, we
test the viability of this model within the constraints of the main belt's low
present-day mass and orbital structure. While previous studies modeled
asteroids as massless test particles because of limited computing power, our
work uses GPU (Graphics Processing Unit) acceleration to model a fully
self-gravitating asteroid belt. We find that depletion in the main belt is
related to the giant planets' exact evolution within the orbital instability.
Simulations that produce the closest matches to the giant planets' current
orbits deplete the main belt by two to three orders of magnitude. These
simulated asteroid belts are also good matches to the actual asteroid belt in
terms of their radial mixing and broad orbital structure.
