Zoe Leinhardt
DAMTP Cambridge

Collisions in the Outer Solar System

Numerical and analytical models for planetesimal evolution focus on
the criteria for accretion and erosion. Studies of the catastrophic
disruption criteria have, in general, used homogeneous, non-porous
materials. The results from the impact experiments are used to
construct simple rules to determine the collision outcome in numerical
simulations of planet formation. However, the catastrophic disruption
threshold should change as the protoplanetary nebula evolves and the
collision velocities increase from subsonic to supersonic, initially
porous planetesimals are compacted into objects with little void
space, and solid, monolithic, non-porous bodies are disrupted into
rubble piles.

We have explored the possible range of variablility in disruption
criteria under conditions expected during planet formation and find
that the catastrophic disruption criteria for bodies smaller than ~100
km changes dramatically during the formation and evolution of the
solar system. Initially, planetesimals are much weaker than previously
assumed. As a result, we suggest that planetesimal growth requires
more than collisions alone.