Mars experienced a dynamo process that generated a global magnetic field ~4.3–3.6 Ga. The cessation of this dynamo strongly impacted Mars’ history and is expected to be linked to thermochemical evolution of Mars’ iron-rich liquid core, which is strongly influenced by its thermal conductivity. Here we directly measured thermal conductivities of solid iron-sulfur alloys to pressures relevant to the Martian core and temperatures to 1023 K. Our results show that a Martian core with 16 wt% sulfur has a thermal conductivity of ~19 to 32 W m-1 K-1 from its top to the center, much higher than previously inferred from electrical resistivity measurements. Our modelled thermal conductivity profile throughout the Martian deep-mantle and core indicates a ~4 to 6-fold discontinuity across the core-mantle-boundary. The core’s efficient cooling resulting from the depth-dependent, high conductivity diminishes thermal convection and forms thermal stratification, significantly contributing to cessation of Martian dynamo.

A document by Wen-Pin Hsieh. Click on the document to view its contents.

The core of terrestrial planets, including Earth, Mars, and Mercury, etc., is majorly composed of iron alloyed with some lighter elements, such as silicon, sulfur, carbon, oxygen, and hydrogen. Core's thermal conductivity plays a key role in controlling its cooling rate, dynamics, thermochemical and dynamo evolution, as well as available energy budget to power dynamo for magnetic field. Recent successful advances in coupling an ultrafast optical pump-probe method with externally-and laser-heated diamond anvil cells have enabled us to precisely and systematically measure the thermal conductivity of a number of candidate core materials in terrestrial planets. With data modelling, we have created the first version of thermal conductivity profiles in the deep interiors of Earth and Mars, with potential critical impacts on their core's thermochemical and dynamo evolution. We acknowledge funding support from the Academia Sinica and the National Science and Technology Council of Taiwan, Republic of China, under Contract AS-IA-111-M02 and 113-2628-M-001-013-. The works presented here are also co-authored with Jung