Rocky planets are layered worlds consisting of various chemical and physical compositions changing with depth through the crust, mantle, and core. The composition of each of these components plays an important role in the thermal and magmatic evolution of the planet. The crust, and sometimes the mantle, of a planet can often be directly sampled or studied remotely. Planetary cores, however, are impossible to directly sample and must be studied through experiments that mimic the likely pressures, temperatures, and compositions present in the cores. In a recent study led by Kathleen Vander Kaaden of Jacobs Engineering Group at NASA Johnson Space Center, the composition of Mercury’s core was investigated with a specific focus on the light elements carbon (C) and silicon (Si) that may be present in addition to the major constituents, iron (Fe) and nickel (Ni).

Under the extremely reducing conditions in the inner Solar System, carbon could have been sequestered into the metallic core of Mercury. High-pressure, high-temperature experiments were conducted, and the authors determined that up to 6.4 weight percent carbon could be dissolved in iron-rich metallic melts under temperature and pressure conditions relevant to Mercury’s interior. By comparing the major element abundance ratios from their experiments (C/Si and Fe/Si) with those of known chondritic meteorite types, Vander Kaaden and colleagues suggest that the closest compositional match is to CB chondrites, which are a small group of chondrites with high metal abundances and very reduced compositions. Thus, CB chondrites may represent the initial composition of Mercury during its formation. Such analog studies of the compositions of planetary interiors are critical to understanding how planets form and evolve. READ MORE