The Formation of the Earth and Moon

Giant impacts (collisions between protoplanets) are the most energetic events planets experience and dictate their mass, chemistry, and thermal and rotational states. Giant impacts have a particular significance for Earth as it is thought that the terminal event in Earth’s accretion was an impact that formed the Moon and set the initial conditions for Earth’s subsequent evolution. The giant impact hypothesis has been the leading theory for the origin of the Moon for decades, but current models struggle to explain the Moon's large mass, composition, and isotopic similarity with Earth. Lock will present a new lunar origin model based on the discovery that many giant impacts create a previously unrecognized type of planetary structure, named a synestia. Using simulations of cooling synestias combined with dynamic, thermodynamic, and geochemical calculations, Lock will show that satellite formation from a synestia can produce the principal features of our Moon. Lock will then discuss how Earth recovered after the impact, as the planet cooled and the lunar orbit expanded, to become the pleasant, habitable world we know today.