THE LUNAR MAGMA OCEAN CONCEPT AND THE SOLIDIFICATION OF THE EARTH'S MOON: A PRIMER

The idea that silicate planetary bodies can begin their existence in a molten state stands in stark contrast to the rubble pile model where planetary bodies gradually grow due to space debris that softly accretes under the effects of gravity. The Earth’s Moon is believed to have originally existed in such a molten state, cooling over a timeframe of possibly up to 200 million years in order to reach the predominantly solid form we observe today. Published literature that explains the details of this process of lunar solidification from an initially molten state (the lunar magma ocean hypothesis, or LMO hypothesis) can be challenging to decipher, and different authors employ different definitions of the main LMO parameters required in order to create basic models of LMO solidification. These models can reveal the potential structure—both geochemical and geophysical—of the molten Moon as it cools and solidifies over different pressures and temperatures. Both numerical and experimental approaches have been used, and although there are large similarities across the approaches in estimating the Moon’s solid structure, there are also potentially significant differences.

The goal of this talk is to introduce the LMO hypothesis to those unfamiliar with the magma ocean concept and lunar cooling history, the essential parameters that require defining, and how these parameters have been addressed throughout the last 50 years (since the Apollo 11 mission). Finally, we briefly look at two new models that predict the structure of the lunar interior and what key information remains missing in order to force better constraints on LMO models.

This work was supported by an NSF/GSA Graduate Student Geoscience Grant #13410-22, which is funded by NSF Award #1949901; and an NSF-supported IIE-GIRE fellowship under Grant #1829436.