Physical Properties and Composition of Cores of Terrestrial Planets

Abstract

To constrain the core compositions of terrestrial planets, sound velocity and density of liquid Fe-Ni-S and Fe-Ni-Si alloys were measured up to 14 GPa. Addition of S reduces the P-wave velocity and bulk modulus of liquid Fe-Ni while addition of Si rises the P-wave velocity and does not affect on the bulk modulus in the present pressure range. Based on the obtained elastic properties of liquid Fe-Ni-S and Fe-Ni-Si, the compositions of planetary cores are estimated by matching the planetary geodesy data to 3-7 wt%S or 7-14 wt%Si for Mercury and 30-34 wt%S or 28-33 wt%Si for Mars.