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 composition and isotopic similarity with Earth. I will present a new lunar origin model based on the discovery that high‐energy, high‐angular‐momentum giant impacts can create a previously unrecognized type of planetary structure, named a synestia. Using simulations of cooling synestias combined with dynamic, thermodynamic, and geochemical calculations, I will show that satellite formation from a synestia can produce the principal features of our Moon. Cooling of the synestia drives condensation, producing moonlets that orbit within the synestia, surrounded by tens of bars of bulk silicate Earth vapor. Moonlets equilibrate with bulk silicate Earth vapor at the temperature of silicate vaporization and the pressure of the structure, establishing the lunar isotopic and chemical composition. Eventually, the cooling synestia recedes within the lunar orbit, terminating the main stage of lunar accretion. Our model shifts the paradigm for lunar origin from specifying a certain impact scenario to achieving a Moon‐forming synestia.
Speaker: Simon Lock, Caltech
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