Gibbs energy representations for ices II, III, V, and VI are reported. These were constructed using new measurements of volumes at high pressure over a range of low temperatures combined with calculated vibrational energies grounded in statistical physics. The collection of representations are released within the open source SeaFreeze program, together with the Gibbs representation already known for ice Ih and water. This program allows accurate determination of thermodynamics properties (phase boundaries, density, specific heat, bulk modulus, thermal expansivity, chemical potentials) and seismic wave velocities over the entire range of conditions encountered in hydrospheres in our solar system (130-500 K to 2,300 MPa). These comprehensive representations allow exploration of the rich spectrum of thermodynamic behavior in the H 2 O system. Although these results are broadly applicable in science and engineering, their use is particularly relevant to habitability analysis, interior modeling, and future geophysical sounding of water-rich planetary bodies of our solar system and beyond. Key Points:• New X-Ray diffraction measurements covering the entire range of ice II, III, V and VI using state of the art high pressure techniques • The first Gibbs energy equations of states for ice II, III, V and VI (and first equations of state for ice II, III and V) • New open-source code SeaFreeze allows to explore water and ices thermodynamic at all conditions found in solar system planetary hydrospheres Supporting Information:• Supporting Information S1

Sodium chloride is expected to be found on many of the surfaces of icy moons like Europa and Ganymede. However, spectral identification remains elusive as the known NaCl-bearing phases cannot match current observations, which require higher number of water of hydration. Working at relevant conditions for icy worlds, we report the characterization of three “hyperhydrated” sodium chloride (SC) hydrates, and refined two crystal structures [2NaCl·17H 2 O (SC8.5); NaCl·13H 2 O (SC13)]. We found that the dissociation of Na + and Cl − ions within these crystal lattices allows for the high incorporation of water molecules and thus explain their hyperhydration. This finding suggests that a great diversity of hyperhydrated crystalline phases of common salts might be found at similar conditions. Thermodynamic constraints indicate that SC8.5 is stable at room pressure below 235 K, and it could be the most abundant NaCl hydrate on icy moon surfaces like Europa, Titan, Ganymede, Callisto, Enceladus, or Ceres. The finding of these hyperhydrated structures represents a major update to the H 2 O–NaCl phase diagram. These hyperhydrated structures provide an explanation for the mismatch between the remote observations of the surface of Europa and Ganymede and previously available data on NaCl solids. It also underlines the urgent need for mineralogical exploration and spectral data on hyperhydrates at relevant conditions to help future icy world exploration by space missions.