We are proposing a model in which the dense ilemnite-rich cumulates that form the last residual of the magma ocean sink to the center of the Moon to form a core. This magma ocean residual is highly enriched in incompatible heat producing elements such as U and Th. Radioactive heating of the core causes thermal instability of the overlying mantle which, as it rises, melts to generate mare basalt magma. Chemical stratification of the mantle traps radioactively generated heat at depth allowing the lithosphere to thicken rapidly enough to explain the lunar mascons. This recently completed study, illustrated in the accompanying animation, is a numerical simulation of a stably stratified fluid heated from below.
Colors show the chemical stratification and contours are isotherms.
Heated fluid at the bottom boundary rises through the stable stratification until it finds a level of neutral buoyancy. It then cools and sinks. This repeated rising and falling motion creates a heated and mixed layer of fluid. We want to study how the thickening rate of this layer depends on various physical parameters such as the strength of the initial stable stratification. Click here for an animation - 2.4 MB 90 second Quicktime movie.