High-Obliquity Early Earth Revisited

Cuk et al. (2016) presented a model in which the Moon tidally evolves from an initially high-angular momentum, high-obliquity Earth. Due to high obliquity, the Moon's evolution stalls at the chaotic transition between equatorial and ecliptic Laplace planes, resulting in angular momentum loss, excitation of lunar inclination, and reduction of Earth's obliquity. Recently, Tian and Wisdom (2020) have shown that the dynamics during the Laplace plane transition should conserve angular momentum perpendicular to the ecliptic. They found that large loss of angular momentum, excitation of lunar inclination, and reduction of obliquity all still happen, but conclude that present Earth-Moon system cannot be reached through the chaotic dynamics of the Laplace plane transition. We revisited the work of Cuk et al. (2016), and found that a low-precision treatment of Earth's precession produced large errors during the Laplace plane transition when the Moon was in a form of Kozai resonance, and its torques lacked many of the usual symmetries. Our corrected code preserves the ecliptic angular momentum, but we do not confirm other conclusions of Tian and Wisdom (2020) about the non-viability of the hypothesis of high-obliquity early Earth. At the meeting we will present our corrected results and discuss the implications for lunar formation and early tidal evolution.