High Pressure Behaviors of Dense Planetary Mixtures

Hydrogen (H₂) and helium (He) are two most fundamental solids abundant in the Universe. Compression behaviors of H₂ and He are critical to understand many body effects of these quantum solids; develop new condensed matter theories; and get insights into the internal structure of the Giant planets. In contrast to a rapid progress in understanding the phase diagram of H₂ at high pressures, a little is known about the phase behavior of planetary mixtures including the most fundamental quantum solids, H₂ and He. In this talk, we will describe our recent studies on high pressure behaviors of several systems of planetary mixtures including H₂-He, H₂-N₂, He-N₂, and H₂-H₂O. The results underscore a significant level of mixing in these planetary mixtures and thereby strong chemical interactions of the interstitial-filled guest H₂ with the host lattices of He, N₂ and H₂O. Based on these results we will point out several fundamental principles governing the pressure-induced phase and chemical transformations in the planetary mixtures, which include strong repulsive interaction, entropically driven phase mixing, proton exchange and ordering, and kinetic-controlled metastable phases.