Probing the Role of Water in Shaping Planetary Mantles

Observations of polluted white dwarf spectra give insight into the composition of terrestrial exoplanet populations which reveals the retention of volatile elements throughout planetary destruction, such as C, S, N, and possibly even water [1]. Volatile retention during the violent breakup of exoplanets may be attributed to the amorphous aluminosilicate network of silicate melts, which provides an efficient means of incorporating volatiles in their structures not available to crystalline silicates at high pressure and temperatures [2]. The incorporation of volatiles in the melts affects the thermodynamic properties of the material, which has not been reflected in the equations of state used to model planetary mantles. Here, we present the results of shock compression experiments on SiO2, an endmember of all silicate magmas produced in terrestrial mantles. Our study focuses on both anhydrous and hydrated (1000 ppm H2O) vitreous SiO2 samples, as water is known to play a major role in the dynamics of Earth’s mantle [3]. We performed gas gun shock release experiments at the Shock Thermodynamics Applied Research Facility at Sandia National Labs to reach pressures up to 200 GPa and determine the density and compressibility (soundspeed) of silicate melts at pressure and temperature conditions throughout rocky planet mantles.

[1] Hoskin et al. (September 2020). MNRAS

[2] Clark et al. (September 2023). AIP

[3] Ohtani & Ishii. (December 2024). PEPS