MELT DROPLET FORMATION IN ENERGETIC IMPACT EVENTS

IT has long been known that impact between rocky bodies at velocities of greater-than-or-similar-to 15 km s-1 can melt or vaporize both the impacting object and a portion of the target 1. We have recently shown 2,3 that geological materials initially shocked to high pressure approach the liquid-vapour phase boundary from the liquid side as they decompress, breaking up into an expanding spray of liquid droplets. Here we present a simple theory for estimating the sizes of these droplets as a function of impactor size and velocity, and show that these sizes are consistent with observations of microtektites and spherules found in the Cretaceous/Tertiary boundary layer.