Phase transitions in mantle silicates and the internal structure of terrestrial exoplanets

The highest-pressure form in the Earth of the major mantle silicate MgSiO₃-bridgmanite is post-perovskite (PPv). Knowledge of the fate of PPv at higher pressures relevant for super-Earth-type planets is fundamental for us to start modeling the internal structure and dynamics of these planets. In this talk I will review the sequence of phase transitions we discovered in pure MgSiO₃ up to 4 TPa, as well as in aggregates of MgSiO₃+MgO and MgSiO₃+SiO₂ with variable Mg/Si abundances. New phases in the (MgO)_n(SiO₂)_m system have been discovered [1-5]. Such phases involve dissociation and recombination reactions in the MgSiO₃+MgO+SiO₂ system, some of them very surprising, but all ending-up in the dissociated elementary oxides, MgO+SiO₂, above 3.1 TPa [1]. These transitions produce density discontinuities in planetary interiors and the consequences of these transitions for the internal structure of terrestrial planets [6] with up to 20 Earth masses will be discussed.

References
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2. K. Umemoto and R. M. Wentzcovitch, Earth Planet. Sci. Lett. 311, 225 (2011).
3. S. Q. Wu et al., J. Phys. Condensed Matter 26, 035402 (2014).
4. H. Niu, et al.,Sci. Rep. 5, 18347 (2015).
5. K. Umemoto et al., Earth Planet. Sci. Lett. 478, 40 (2017).
6. A. P. van den Berg et al., Icarus 317, 412 (2019).