Diffusivity of heavy elements in Jupiter and Saturn

Recent work has suggested that gas giant planets such as Jupiter and Saturn may not consist of a small number of fully convective and chemically homogenous layers as has been conventionally assumed, but instead may be chemically inhomogeneous with convective redistribution of elements limited by semiconvection. Constructing accurate planetary models which include semiconvective processes requires accurate estimates of the diffusion constants of minority chemical species in planetary fluids, which have not previously been available. In this work we use ab initio density functional molecular dynamics simulations to simulate the diffusion of heavy elements (specifically carbon, silicon, iron) in hydrogen–helium mixtures at conditions corresponding to giant planet deep interiors. We find diffusivities at the high end of the previously proposed range, and estimate that semiconvective processes may be able to redistribute a substantial fraction of Jupiter’s core mass within the planet’s age.