Theia's date with destiny: possible conditions leading to a Giant Impact

The Giant Impact theory is the leading explanation for the Moon's origin, but mysteries remain in the conditions leading up to the event. Collisions were common during the turbulent infancy of the Solar System and led to a small set of terrestrial planets. Dr. Quarles presents a numerical model that considers the penultimate orbits of the Solar System, when five terrestrial planets are present. From this model, he indicates which starting parameters for Theia (the proto-Moon) result in a late Giant Impact consistent with physical dating constraints. He also finds that the likely semimajor axis of Theia, at the epoch when the simulations begin, depends on the assumed mass ratio of the Earth-Moon progenitors (8/1, 4/1, or 1/1). The low eccentricities of the resulting terrestrial planets are most commonly produced when the progenitors have similar semimajor axes at the epoch when the model starts. Additionally, Dr. Quarles will show that perturbations from the giant planets can affect the dynamical evolution of the system leading to a late Moon Forming Giant Impact.