Salt- and gas-filled ices under planetary conditions

Abstract

In recent years, evidence has emerged that solid water can contain substantial amounts of guest species, such as small gas molecules—in gas hydrate structures—or ions—in salty ice structures—and that these ‘filled’ ice structures can be stable under pressures of tens of Gigapascals and temperatures of hundreds of Kelvins. The inclusion of guest species can strongly modify the density, vibrational, diffusive and conductivity properties of ice under high pressure, and promote novel exotic properties. In this review, we discuss our experimental findings and molecular dynamics simulation results on the structures formed by salt- and gas-filled ices, their unusual properties, and the unexpected dynamical phenomena observed under pressure and temperature conditions relevant for planetary interiors modelling. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets’.

Assembly of clathrates from tetrahedral patchy colloids with narrow patches

“…2(j)] and only a tiny amount of 5 12 6 2 , 5 12 6 3 , and 5 12 6 4 cages, typical of sI, sII, and amorphous water clathrates. 29,30 Consistently, the growth of the aggregate is not correlated with an increase of sI, sII, or amorphous clathrate vertices. On the contrary, there is a rather pronounced enhancement of the number of vertices compatible with the three shell icosahedral cluster [ Fig.…”

Overview of the recent studies on high‐pressure impurity ices

“…[49] As mentioned above, investigations on the high-pressure phase diagrams of salty ices were energetically carried out in the last decade. [48,50,51] Briefly, distinct discoveries in their studies are that high-pressure ice VII can incorporate LiCl salt as Li + and Cl À ions in the ice lattice under highpressure upon warming, rather than being expelled out into the grain boundaries of ice. [26] Klots et al [52,53] proved that salts such as LiBr and NaCl could come from salty ice under their eutectic composition.…”

“…Bove et al [ 48 ] stated that the studies on the phase diagram of salty ices are only at an early stage. Thus, this subject needs further detailed studies, including the thermal and electrical conductivity properties of these salty ices.…”

“…[10] Work of clathrate hydrates in the low-pressure range has also been extensively reviewed by E. D. Sloan, [39] and there have been many importan reports. [40][41][42][43][44][45][46] Supercooled liquids, including amorphous ices, were reviewed by J. T. Fourkas et al [47] Excellent studies on salty ices with imaginative ideas and experiments were recently reviewed by Bove et al [48] However, many vibrational studies have not been on high-pressure ices with salt as impurities. We, therefore, overview this issue further along with our contributing Raman studies.…”

A High-pressure Filled Ice in the H2O–CO2–CH4 System, with Possible Consequences for the CO2–CH4 Biosignature Pair

“…Therefore, their potential formation is likely to have an effect on the transport of volatiles across high-pressure ice mantles and on the outgassing of secondary atmospheres around water worlds. The filled-ice structure is related to a low-pressure water-ice polymorph (based on ice Ic, II and Ih: ice Ih is the phase I of water ice having a hexagonal unit cell, also known as ordinary ice; ice Ic differs by having a cubic unit cell; and Ice II is the second phase of water ice), stabilized at high pressure by its guest molecules (Bove & Ranieri 2019). Clathrate hydrates tend to form a filled ice upon increasing the pressure, making the latter more relevant for the study of ocean planet interiors.…”