The Collisional Accretion of Planets: A Shock Physics Story

Collisions play a central role in the growth of rocky planets from planetesimals. As the bodies grow, the mutual impact velocities increase from a subsonic mechanical regime to a shock-induced vaporization regime at 10’s km/s. Today, the most extreme natural impact pressures can be reached at high energy facilities such as the Z machine, the Omega and Omega EP lasers, and the National Ignition Facility, and I will summarize recent advances and challenges in experimental work on probing the shock Hugoniots and phase boundaries of planetary materials using these facilities. The irreversible work deposited by the shock-and-release thermodynamic path induces widespread melting and vaporization in the colliding bodies. I will highlight recent insights on the effects of shock-induced phase changes on planetesimals, which survive as bodies in the asteroid belt, and on the origin of the Earth and Moon.