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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

A growing number of satellites in the outer solar system likely have global oceans beneath their outer icy shells. While the presence of liquid water makes these ocean worlds compelling astrobiological targets, the exchange of heat and materials between the deep interior and the surface also plays a critical role in promoting habitable environments. In this article, we combine geophysical, geochemical, and geological observations of the Jovian satellites Europa, Ganymede, and Callisto as well as the Saturnian satellites Enceladus

Under ReviewEnceladus is believed to have a saltwater global ocean with a mean depth of at least 30 km [1,2], heated from below at the ocean-core interface and cooled at the top [3], where the ocean loses heat to the icy lithosphere above. This scenario suggests an important role for vertical convection to influence the interior properties and circulation of Enceladus' ocean. Additionally, the ice shell that encompasses the ocean has dramatic meridional thickness variations that, in steady state, must be sustained against processes acting to remove these ice thickness anomalies. One mechanism that would maintain variations in the ice shell thickness involves spatially-separated regions of freezing and melting at the ocean-ice interface. Here, we use an idealized, dynamical ocean model forced by an observationally-guided density forcing at the ocean-ice interface to argue that Enceladus' interior ocean should support a meridional overturning circulation. This circulation establishes an interior density structure that is more complex than in studies that have focused only on convection, including a shallow freshwater lens in the polar regions. Spatially-separated sites of ice formation and melt enable Enceladus to sustain a significant vertical and horizontal stratification, which impacts interior heat transport, and is critical for understanding the relationship between a global ocean and the planetary energy budget. The presence of low salinity layers near the polar ocean-ice interface also influences whether samples measured from the plumes [4] are representative of the global ocean.

Neptune's largest moon Triton (radius 𝐴𝐴 𝐴𝐴𝑇𝑇 = 1, 353 km) is thought to be an erstwhile Kuiper belt object that was captured by the ice giant (Agnor & Hamilton, 2006). Orbiting at a radial distance of 𝐴𝐴 14.4𝑅𝑅𝑁𝑁 (radius of Neptune 𝐴𝐴 𝐴𝐴𝑁𝑁 = 24, 622 km), Triton is always located within Neptune's magnetosphere (Curtis & Ness, 1986;Mejnertsen et al., 2016;Ness et al., 1989;Richardson, 1993). The moon's highly inclined orbit-tilted nearly 𝐴𝐴 157 • with respect to its parent planet's rotational equator-results in a retrograde orbital motion around Neptune. Triton possesses the second-most dense moon atmosphere in the solar system after Titan (Broadfoot et al., 1989;Strobel et al., 1990;Strobel & Zhu, 2017). Mainly comprised of neutral 𝐴𝐴 N2 , its maximum surface number density is on the order of 𝐴𝐴 10 15 cm −3 , with a scale height between 10 and 70 km (Broadfoot et al., 1989). Additionally, trace gases including methane are present, with surface densities below 𝐴𝐴 10 11 cm −3 (e.g., Summers & Strobel, 1991;Trafton, 1984;Krasnopolsky et al., 1992). This neutral envelope is predominantly ionized by a combination of magnetospheric electron impacts and photoionization, resulting in an ionospheric Pedersen conductance that may exceed 𝐴𝐴 10 4 S (Strobel et al., 1990). In addition to this global atmosphere, observations during the Voyager 2 encounter of Neptune in 1989 indicated localized, geyser-like vapor plumes emanating from the surface to an altitude of ∼10 km (Smith et al., 1989). Since the moon's interior is likely differentiated in a hydrosphere and rocky mantle, it is possible that these plumes originate from a global, deep ocean sustained via radiogenic heating and/or tidal forcing (Nimmo & Spencer, 2015).