Impacts into porous foam targets: possible implications for the disruption of comet nuclei

We have conducted a series of impact experiments to examine the response of very porous foam targets to various impacts. Under near-vacuum conditions, closed-pore and open-pore foam targets were subjected to ∼1 km s−1 impacts from aluminum and foam projectiles. We found that open-pore targets absorbed the impacts with little or no global fragmentation or noticeable cratering, exhibiting only local damage along the path of the projectile, which tunneled through the target. Closed-pore targets exhibited nearly explosive disruption, apparently resulting from stresses built up within the target due to internal pressurization from air that could not escape the target interior during evacuation of the impact chamber. These results suggest that build-up of internal volatile pressure within the nuclei of collisionally or dynamically unevolved comets could allow comparatively small impacts onto their surfaces to result in disproportionately disruptive outcomes.