High Resolution Models of Magnetized, Moon-Forming Giant Impacts

Charles Gammie, University of Illinois at Urbana-Champaign

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The leading theory for the formation of Earth's Moon suggests that a Mars-sized impactor, Theia, struck the proto-Earth in an oblique collision ~4.5 billion years ago. The debris from this impact, comprised of melted and vaporized silicates, was sent into Keplerian orbits about the proto-Earth. It is from this protolunar disk the Moon is thought to have condensed. Numerical simulations have been previously performed modeling this giant impact, however, none have considered the dynamical importance of any magnetic field the impactor or target may have possessed. Hot debris material from the impact will be well coupled to the magnetic field, which could lead to a different impact outcome compared to present simulations. Impact simulations performed with time awarded during the Spring 2018 Blue Waters exploratory awards demonstrate that the protolunar disk is subject to (1) magnetic field amplification from shear, most prominent at the interface between the proto-Earth's rapidly rotating surface and the innermost Keplerian orbits of the protolunar disk, and (2) the magnetorotational instability, which could produce exponential growth of field strengths. We propose to continue with these 3-D simulations of magnetized giant impacts, (1) running at unprecedented linear resolution, (2) pushing out the simulations further in time in order to capture the growth of magnetically-driven turbulence in the disk, while altogether (3) incorporating new physics, including realistic equations of state (i.e., for iron and silicates), resistive magnetohydrodynamics, and the evolution of multiple materials.