Cores of the Terrestrial Planets

The compositions of the cores of the terrestrial planets have been re-examined following a calculation by O. G. Soroktin that the iron oxide Fe₂O is stable at pressures reached in the Earth's core and his suggestion that the outer core may consist of Fe₂O. It is shown that the idea of an Fe₂O outer core in the Earth can be fairly well reconciled with a common overall composition for the planets Earth, Venus and Mars in a way that avoids the main objections to the earlier phase-transition theory.