Precessionaly driven instability in the Lunar core.

Abstract:

Since Yoder 1981, the large dissipation at the period of precession associated with the misalignment of the lunar rotation axis with respect to the Cassini plan has been attributed to turbulent mixing in a liquid outer core. However, no precession driven instability mechanism supported this scenario without invoking unrealistic Core-Mantle boundary ellipticity.

Meanwhile, recent numerical simulations (Lin et al., PoF 2014) and experiments (Goto et al., JFM 2014) have shown that internal shear layers spawned by the viscous boundary in a precessing spherical liquid shell can generate parametric-like instabilities. Based on the consistent scaling laws proposed in these two studies, we show that the present Lunar core is highly super critical, hence supporting the idea of turbulent dissipation.

In my presentation I will briefly review the observations suggesting the presence of a large dissipation at the period of precession in the lunar core and present the shear driven instability mechanism, showing that precession driven turbulence is indeed plausible.