Antonangeli, Daniele ; Badro, James ; Boccato, Silvia ; Morard, Guillaume ; Rivoldini, Attilio ; Russell, Christopher T. ; Siebert, Julien ; Xu, Fang

Talk presented at American Geophysical Union Fall Meeting 2019 San Francisco on 2019-12-12

Abstract: InSight is going to provide geophysical and geodetic constraints on the solid or liquid nature and size of the Martian core. In order to produce a compositional model of the core, observations have to be complemented by the chemical and physical properties of the constituent materials at pertinent thermodynamic conditions. Further independent constraints can also come from core formation models. We thus performed experiments probing density of liquid iron alloys at high pressure and at high temperature, and experiments probing metal-silicate partitioning over and extended pressure and temperature range, so to provide the mineral physics and petrological data necessary to the modeling of Mars core. Here we present multi-parameter continuous core formation models based on core-mantle equilibrium using thermodynamic parameterization of high-pressure, high-temperature metal-silicate partitioning experiments. In our models the final equilibration depth is varied from 0 to 25 GPa, the temperature between that of Martian mantle solidus and liquidus, and we varied the initial magma ocean composition while always converging to a final FeO concentration constrained by present-day mantle composition models. All models successfully matching the abundance of siderophile trace elements in bulk silicate Mars point to a final equilibration depth larger than 14 GPa, high temperatures, and a constant FeO concentration in the mantle during core segregation. These conditions have direct implications on the nature and abundance of light elements in the core: Mars’ core cannot contain a significant amount of silicon, and major light elements are sulfur and oxygen, with the abundance of the latter increasing with that of the former. We further reduced the oxygen-sulfur compositional space resulting from core formation models by retaining only solutions that, according to thermodynamic modeling based on high-pressure, high-temperature density and compressibility measurements on liquid Fe-S and Fe-O alloys, agree with available geodetic data. Finally the possibility to detect a core-generated magnetic signal is addressed.