The Dynamical Evolution of the Earth-Moon Progenitors

The Giant Impact Hypothesis was introduced in the mid-1970's after consideration of results from the Apollo Moon missions. This hypothesis best explains the similarity in elemental proportions in lunar and terrestrial rocks, the depletion of lunar volatiles, the lack of lunar iron. and the large angular momentum in the Earth-Moon system. Comparison between the radiometric ages of inclusions in the most primitive meteorites and those of inclusions in the oldest lunar rocks and the differentiation age of Earth suggests that the Earth-Moon system formed about 100 Myr after the oldest meteorites. In addition, the age of the famous Martian meteorite ALH84001 and an early solidification time estimated from the Martian crust, suggest that the inner Solar System was fairly clear of large bodies about 10 Myr after the oldest meteorites formed. Thus, the 'standard model' suggests that for a period of several tens of millions of years the terrestrial planet region had few. if any, lunar-sized bodies and there were five terrestrial planets, Mercury, Venus, the two progenitors of the Earth-Moon system, and Mars. To simulate the dynamics of the Solar System before the hypothesized Moon-forming impact, we are integrating the Solar System with the Earth-Moon system replaced by two bodies in heliocentric orbits between Venus and Mars. The total (orbital) angular momentum of the Earth-Moon progenitors is that of the present Earth-Moon system, and their total mass is that of the Earth-Moon system. We are looking at ranges in mass ratio and initial values for eccentricity, inclination. and semi-major axis. We are using the SYMBA integrator to integrate these systems until a collision occurs or a time of 200 Myr elapses. Results are presented in a companion paper.