The magma ocean stage in planetary formation is where most or all of a planetary body is molten, allowing for the separation of minerals and ultimately the formation of the silicate mantle as it cools. Physical properties of the silicate melt, such as viscosity, control the crystallization process where less viscous liquids allow for more separation of minerals into distinct compositional layers within the magma body. In order to understand the compositionally diverse surface of Mercury, the resulting interior structure formed from the magma ocean stage needed to be modeled, starting with the viscosity of the cooling magma ocean liquid.

Researchers from the University of Tennessee explored the solidification of planet Mercury's magma ocean via viscosity experiments on a late-stage magma ocean liquid. Falling sphere viscometry experiments were performed at HPCAT 16-BM-B using the Paris-Edinburgh apparatus, testing silicate compositions analogous to the composition of Mercury’s late-stage magma ocean.  Predictive models were developed so that the viscosity of the compositions could be estimated at different pressure and temperature conditions. Additional geophysical calculations determined how crystals would grow in the magma ocean and if they would sink, float, or be entrained in the liquid. This work has introduced endmember scenarios for Mercury’s mantle structure as a result from the silicate liquid viscosity models and geophysical analyses which provide important constraints to understanding Mercury’s early formation processes and subsequent dynamic volcanic history.

See the full article: https://doi.org/10.1029/2021JE006946

• Mouser, M. D., Dygert, N., Anzures, B. A., Grambling, N. L., Hrubiak, R., Kono, Y., et al. (2021). Experimental investigation of Mercury's magma ocean viscosity: Implications for the formation of Mercury's cumulate mantle, its subsequent dynamic evolution, and crustal petrogenesis. Journal of Geophysical Research: Planets, 126, e2021JE006946