About this Research Topic
Each of these aspects largely depends on the existence of a partially or entirely molten core to generate a (geo)dynamo. Under their respective core pressures, the partially molten cores of Mercury, Venus, Earth, and Mars must contain certain proportions of light elements. For example, Earth’s core is 8–12% less dense than pure Fe-Ni alloy under relevant pressure and temperature conditions, leading to the assumption that it contains significant concentrations of one or more light elements. The major volatile elements are likely candidates, but their abundances in the core have been subject to considerable controversies. Nonetheless, accurate knowledge of volatile concentrations in planetary cores is crucial for modeling the thermal and magnetic field evolution of planets during their early histories.
Planetary core compositions were largely determined during planetary formation, when terrestrial planets underwent one or more magma ocean phases in which they were largely or completely molten. This step was essential in determining core composition because it allowed planetary differentiation, i.e., the segregation of a metal core and the formation of a primitive atmosphere. During core formation, metal droplets partially or fully equilibrated with the surrounding magma ocean, exchanging volatile elements between them. Therefore, the present compositions of terrestrial planets' cores strongly depend on:
• The primordial composition of the planets, i.e., the source of their volatile elements, whether nebular and/or from planetary building blocks and;
• The metal-silicate partitioning coefficients of H, C, N, O, and S, which vary with pressure, temperature, and oxygen fugacity conditions in magma oceans.
For these reasons, volatile abundances are assumed to be varied among the cores of Mercury, Venus, Earth, and Mars.
This Research Topic aims to address advances in the study of H, C, N, O, and S contents in the cores of Mercury, Venus, Earth, and Mars. The Topic Editors welcome high-quality contributions covering experimental studies of H, C, N, O, and/or S partitioning between metal alloys and silicate melts at high pressure and high temperature, and of the effects of these elements on sound velocities and thermal conductivities in planetary cores. Contributions on how the incorporation of volatile elements into planetary cores may have influenced the evolution of core dynamos and planetary magnetic fields are also welcome.
Keywords: terrestrial planets, core formation, differentiation, element partitioning, high-pressure experiments, oxygen fugacity, modeling, light elements, equations of state, sound velocity, thermal conductivity, core dynamo
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