Dynamical evolution of the Earth-Moon Progenitors

The origin of Earth's Moon has been a perplexing mystery for many decades. Lunar samples have been obtained indicating an age of the Moon to be roughly 60-120 Myr [1,2] younger than the Calcium Aluminum Inclusions in the chondritic meteorites. Updated measurements indicate an age difference of 70-110 Myr [3,4]. Additional information has been obtained for the composition of the Moon relative to the Earth, with surprising similarities and differences. However, the complete story of the formation of the Moon has yet to be told. Simulations of a Moon-forming giant impact using smooth particle hydrodynamics have been successful in providing insight into what initial conditions are required with respect to the collision parameters and compositions [5]. But the mass of the impactor is largely unconstrained and can vary depending on the chosen model [6,7]. Using a dynamical 5 terrestrial planet model we present results that constrain some of this uncertainty and indicate a likely spatial origin of the proto-Moon if a mass ratio of 4:1 or 1:1 is assumed between the progenitors.