THE COLLISIONAL DIVOT IN THE KUIPER BELT SIZE DISTRIBUTION

This paper presents the results of collisional evolution calculations for the Kuiper Belt starting from an initial size distribution similar to that produced by accretion simulations of that region-a steep power-law large object size distribution that breaks to a shallower slope at r similar to 1-2 km, with collisional equilibrium achieved for objects r less than or similar to 0.5 km. We find that the break from the steep large object power law causes a divot, or depletion of objects at r similar to 10-20 km, which, in turn, greatly reduces the disruption rate of objects with r greater than or similar to 25-50 km, preserving the steep power-law behavior for objects at this size. Our calculations demonstrate that the roll-over observed in the Kuiper Belt size distribution is naturally explained as an edge of a divot in the size distribution; the radius at which the size distribution transitions away from the power law, and the shape of the divot from our simulations are consistent with the size of the observed roll-over, and size distribution for smaller bodies. Both the kink radius and the radius of the divot center depend on the strength scaling law in the gravity regime for Kuiper Belt objects. These simulations suggest that the sky density of r similar to 1 km objects is similar to 10(6)-10(7) objects per square degree. A detection of the divot in the size distribution would provide a measure of the strength of large Kuiper Belt objects, and constrain the shape of the size distribution at the end of accretion in the Kuiper Belt.