IMPACT CHEMISTRY: A NEW FRONTIER IN SHOCK PHYSICS (Invited Presentation)

Most current impact studies focus on the physical aspects of the cratering process. The mechanics of crater excavation and collapse is well explored by modern hydrocodes, such as iSALE, CTH, or SPH. However, these studies generally neglect the profound chemical changes that may occur in the strongly shocked and heated rocks of both the projectile and target. These materials are subjected to a thermodynamic cycle unlike anything else on Earth. They are first raised to pressures and temperatures that may exceed 300 GPa and 20,000 K, after which they decompress nearly adiabatically to ambient pressure and temperatures that put them in the vapor or liquid phases. During this rapid cycle, entropy increases and the equilibrium between liquid and vapor phases strongly favors elements, such as oxygen, that can enter the vapor phase. The result is a strong chemical reduction of the liquid phase. When such reduced liquids are quenched by the rapid cooling, they record their history in the form of reduced species, such as Fe+2 where the starting material contained Fe+3, or P+3 where P+5 was in the starting material. This reduction accounts for the common green or black colors of tektites, fulgurites and Trinity glass. The dispersion of such reduced species in he form of sand-size glassy spherules over the entire Earth during the Hadean and Archean eras may have played a significant role in the origin of life.