On the Constitution of the Terrestrial Planets

Abstract

It is suggested that the density jump at the boundary of the Earth's core is due to a pressure transition from the molecular to a metallic phase, rather than to the appearance of a new material such as an alloy of iron and nickel. The pressure at the boundary of the core will then be characteristic of the chemical composition of the material, and so may be assumed to be the same for all the terrestrial planets. The mean densities of the terrestrial planets calculated on the basis of this assumption are in good, but not perfect, agreement with the empirical values. The calculated ellipticity of Mars is also satisfactory. If allowance is made for the tendency of the heavier elements to gravitate towards the centre of the Earth, the small discrepancies in the calculated mean densities can be removed.