Electrical Conductivity of Aqueous Magnesium Sulfate at High Pressure and Low Temperature with Application to Ganymede’s Subsurface Ocean

Abstract:

Ganymede has strong evidence of a subsurface ocean primarily composed of MgSO₄. We conducted experimental measurements of the electrical conductivity of aqueous MgSO₄ at 200-1200 MPa and 243-295 K in a multi-anvil press, simulating the high-pressure and low-temperature (HPLT) conditions of Ganymede’s subsurface ocean. A numerical model is proposed with logσ = -3.6196 + 1052.092/T + 0.8755 logc + 2logΛ⁰ - log⁡(5Λ⁰ + 2695c^1⁄2), where σ is electrical conductivity in S/m, T is temperature in K, c is molar concentration in mol/L. Λ⁰ is the limiting equivalent conductance of MgSO₄(aq) at infinite dilution in S·cm²·equiv^-1, Λ⁰ = 2960.96 -126.95ρ - 1365065.31/T + 167580144/T², where ρ is the fluid density in g/cm³. We used this model to generate electrical conductivity curves up to 500 km deep in Ganymede and found that the values are lower than previously expected, suggesting deeper subsurface ocean layers or higher concentration is required to achieve the inductive response. Our experimental methods demonstrate access to the HPLT environment of liquid samples that expands our ability for experimental simulation of icy-ocean worlds in the outer solar system.