Thermoelastic Properties of Liquid Fe‐Rich Alloys Under Martian Core Conditions

Abstract

Seismic measurements made as part of the InSight mission (Banerdt et al., 2020) indicate that Mars' core is large and light with radius and mean density ranging between 1,790 and 1,870 km and 5.7-6.3 g/cm 3 , respectively (Drilleau et al., 2022;Durán et al., 2022;Khan et al., 2022;Stähler et al., 2021). Relative to pure liquid Fe (Kuwayama et al., 2020), this implies a density deficit far in excess of that observed in Earth's core (Birch, 1964). Taken at face value, it requires the incorporation of substantial amounts of light elements (LEs) into the martian core during the early stages of planetary formation (e.g., Khan et al., 2022;Steenstra & van Westrenen, 2018). Previous work that relied mostly on analyses of martian meteorites and cosmochemical arguments (e.g., Lodders

Thermoelastic Properties and Thermal Evolution of the Martian Core From Ab Initio Calculated Magnetic Fe‐S Liquid

“…By selecting 1900, 1600, and 1300 K as the current CMB temperature, the adiabatic pressure and temperature curve (Figure 2a), thermal expansion coefficient (Figure 2b), Grüneisen constant γ (Figure 2c) and thermal expansion coefficients α (Figure 2d) and all the other thermoelastic properties along the adiabatic curve were collected. Temperature and pressure dependent isothermal bulk modulus and thermal expansion coefficient were of the same order as the early reports (Edgington et al., 2019; Hemingway & Driscoll, 2021; Huang et al., 2023), which confirmed our calculated methods of thermoelastic properties. The Grüneisen constant γ is lower than the reported Fe liquid at 3000 K (Huang et al., 2023) and Fe, Fe‐S‐Si at 2000–4000 K (Edgington et al., 2019).…”

“…The S elements addition makes sure that the Fe‐S liquid under the Martian core condition is thoroughly magnetic. The calculated magnetic moments of Fe‐S liquid (Fe concentration is 75 at.%) were higher than those of pure Fe (Edgington et al., 2019; Huang et al., 2023) and Fe 80 S 10 Si 10 liquid (Edgington et al., 2019). The magnetic moment difference between the Fe‐S liquid and the reported ab initio calculated data (Edgington et al., 2019; Huang et al., 2023) is correlated with densities, as shown in Figure 1b.…”

“…The calculated magnetic moments of Fe‐S liquid (Fe concentration is 75 at.%) were higher than those of pure Fe (Edgington et al., 2019; Huang et al., 2023) and Fe 80 S 10 Si 10 liquid (Edgington et al., 2019). The magnetic moment difference between the Fe‐S liquid and the reported ab initio calculated data (Edgington et al., 2019; Huang et al., 2023) is correlated with densities, as shown in Figure 1b. The calculated density of the Fe‐S liquid coincided with the reported Fe‐Ni‐S liquid ( S concentration is 16 wt%) (Kawaguchi et al., 2017) under the same condition.…”

“… The ab initio calculated (a) magnetic moments and (b) densities at different pressures and temperatures. The “Fe H2023,” “Fe E2019,” and “Fe‐S‐Si E2019” labels in subfigure (a) are ab initio calculated data about Fe liquid at 3000 K (Huang et al., 2023), Fe liquid at 2000 K (Edgington et al., 2019) and Fe‐S‐Si liquid at 2000 K (Edgington et al., 2019), respectively. The “1900 K, K2017” and “2300 K, K2017” labels in subfigure (b) are experimental data about Fe‐Ni‐S liquid with 16 wt.% S concentration (Kawaguchi et al., 2017).…”

“…In view of numerical calculation, the magnetic and thermoelastic properties of Fe 80 S 10 Si 10 liquid at 5.5–60 GPa and 2000–4000 K were calculated by ab initio molecular dynamics simulations (Edgington et al., 2019). The elastic properties of the Fe‐X (X = Ni, S, C, O, and H) mixture liquid at 19 and 35 GPa/2400 K were calculated using ab initio molecular dynamics simulations (Huang et al., 2023). However, the analytic representation equation of the state and thermoelastic properties of Fe‐S liquid with the Martian core S concentration and state condition were never explored.…”