Is the mantle soluble in the core?

It is pointed out through the application of elementary solubility theory that, at the mantlecore interface conditions of 1.35 Mb and a temperature of 4400°K (estimated solely from the measured seismic velocities), magnesium oxide could be soluble to an extent of about 10% in liquid iron. Such solubility considerations put stringent constraints on the chemical constitution of the earth because, for example, neither SiO2 nor Mg2SiO4 is calculated to be sufficiently soluble to lower the density of the liquid core significantly below that of pure iron.