  The size distribution of small asteroids in the Main Belt is assumed to be
determined by an equilibrium between the creation of new bodies out of the
impact debris of larger asteroids and the destruction of small asteroids by
collisions with smaller projectiles. However, for a diameter less than 6 km we
find that YORP-induced rotational disruption significantly contributes to the
erosion even exceeding the effects of collisional fragmentation. Including this
additional grinding mechanism in a collision evolution model for the asteroid
belt, we generate size-frequency distributions from either an accretional
(Weidenschilling, 2011) or an "Asteroids were born big" (Morbidelli, 2009)
initial size-frequency distribution that are consistent with observations
reported in Gladman et al. (2009). Rotational disruption is a new mechanism
that must be included in all future collisional evolution models of asteroids.
