Do cometesimal collisions lead to bound rubble piles or to aggregates held together by gravity?

Although the collisions of cometesimals have been widely discussed in the context of the so-called "rubble-pile" model of comet nuclei, there has been little discussion of the physical consequences of collisions between cometesimals, Here we calculate analytically the compressive strength of grain aggregates which compose the cometesimals and discuss possible consequences of collisions of cometesimals, It is shown that heterogeneity in density results from collisions between cometesimals in a protoplanetary nebula and that the forces necessary to separate the merged cometesimals are orders of magnitude larger than gravitational attraction. Similarly, substantial compaction takes place in the regions of the Kuiper belt and the collisions result in relatively tightly bound aggregates. (C) 2000 Academic Press.