Early evolution of the Earth–Moon system with a fast-spinning Earth
Wisdom et al
The isotopic similarity of the Earth and Moon has motivated a recent investigation of the formation of the Moon with a fast-spinning Earth (Cuk, M., Stewart, S.T., . Science, doi:10.1126/science.1225542). Angular momentum was found to be drained from the system through a resonance between the Moon and Sun. They found a narrow range of parameters that gave results consistent with the current angular momentum of the Earth–Moon system. However, a tidal model was used that was described as approximating a constant Q tidal model, but it was not a constant Q model. Here we use a conventional constant Q tidal model to explore the process. We find that there is still a narrow range of parameters in which angular momentum is withdrawn from the system that corresponds roughly to the range found earlier, but the final angular momentum is too low to be consistent with the Earth–Moon system. Exploring a broader range of parameters we find a new phenomenon, not found in the earlier work, that extracts angular momentum from the Earth–Moon system over a broader range of parameters. The final angular momentum is more consistent with the actual angular momentum of the Earth–Moon system. We develop a simple model that exhibits the phenomenon.