Rapid solidification of Earth?s magma ocean limits early lunar recession

The early evolution of the Earth-Moon system prescribes the tidal environment of the Hadean Earth and holds the key to the formation mechanism of the Moon and its thermal evolution. Estimating its early state by backtracking from the present, however, suffers from substantial uncertainties associated with ocean tides. Tidal evolution during the solidification of Earth's magma ocean, on the other hand, has the potential to provide robust constraints on the Earth-Moon system before the appearance of a water ocean. Here we show that energy dissipation in a solidifying magma ocean results in considerably more limited lunar recession than previously thought, and that the Moon was probably still at the distance of -7-9 Earth radii at the end of solidification. This limited early recession aggravates the often overlooked difficulty of modeling tidal dissipation in Earth's first billion years, but it also offers a new possibility of resolving the lunar inclination problem by allowing the operation of multiple excitation mechanisms.

Automated summary

The early evolution of the Earth-Moon system is crucial for understanding the formation and thermal evolution of the Moon. Estimating its early state based on the present suffers from uncertainties related to ocean tides. However, studying tidal evolution during the solidification of Earth's magma ocean can provide robust constraints on the system. We found that energy dissipation during solidification leads to limited lunar recession, suggesting the Moon was still close to the Earth at the end of solidification. This has implications for modeling tidal dissipation in Earth's first billion years and provides new possibilities for resolving the lunar inclination problem.