Laboratory simulations of large scale fragmentation events

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Experimental studies of catastrophic fragmentation are necessarily limited to centimeter-sized targets. This, coupled with uncertainties in the scaling relationships for fragmentation, have made it difficult to estimate the conditions required to collisionally disrupt large asteroids or planetary satellites. A fundamental uncertainty arises because the results for small scale experiments are dominated by the strength of the target, while sufficiently large bodies are dominated by the pressure due to gravitational forces. This paper summarizes the results of fragmentation experiments conducted at elevated external pressure. By applying the appropriate overpressure to a small target, an experiment matches the lithostatic compressive stress which exists in the interior of a larger body. For example, the largest overpressure used in the tests corresponds to the volume-averaged lithostatic stress inside a 460-km diameter body. As the overpressure is increased, the fragmentation transitions from a regime dominated by material strength to one dominated by the applied overpressure. An analogy is made to the transition from strength to gravity effects. The high pressure tests allow direct measurement of the energy per unit target mass required to catastrophically fragment a body subject to large compressive stresses. These specific energies compare well with those estimated from observations of the Themis, Eos, and Koronis families.