Shock equation of state and critical vaporization of MgSiO3 from ab initio simulations

Giant impacts in the final stage of planet formation could induce partial melting and vaporization of colliding bodies. However, the critical conditions required for the vaporization of constituent materials as well as the fraction of material that undergoes vaporization during such impacts remain uncertain. In this work, we present the shock equation of state and critical vaporization of MgSiO3, the most abundant mineral in the lower mantle, using first-principles molecular dynamics. The critical point of MgSiO3 is determined to be 7093 f 41 K and 0.73 f 0.05 g cm-3. The behavior of the Hugoniot curve is investigated under different initial conditions. We find that the critical shock pressure required to vaporize MgSiO3 under ambient conditions is 253 f 27 GPa, whereas a warm initial state of 1 GPa and 1500 K reduces this value to 152 f 8 GPa. The corresponding impact velocities necessary to achieve vaporization are estimated to be 9.3 km s-1for an iron projectile and 11.8 km s-1for a forsterite projectile under ambient conditions and reduce to 7.3 and 9.1 km s-1, respectively, under the warm initial state. Our findings indicate that giant impacts could vaporize a substantial portion of mantle materials, thereby facilitating compositional mixing and chemical equilibration within the mantle.