Chemistry of Frozen Sodium–magnesium–sulfate–chloride Brines: Implications for Surface Expression of Europa’s Ocean Composition

Abstract

The composition of Europa's subsurface ocean is a critical determinant of its habitability. However, our current understanding of the ocean composition is limited to its expression on the surface. This work investigates experimentally the composition of mixed sodium-magnesium-sulfate-chloride solutions when frozen to 100 K, simulating conditions that likely occur as ocean fluids are emplaced onto Europa's surface. Micro-Raman spectroscopy is used to characterize phase composition of the frozen brines at 100 K.

Raman detection of hydrohalite formation: Avoiding accidents on icy roads by deicing where salt will not work

“…Therefore, intensive research is ongoing to examine the chemistry and materials composition of Europa's surface and subsurface ocean. and 3420 cm -1 [12], [36]. The latter strong band exhibited shoulders at about 3403-3405 and 3435 cm -1 , in good agreement with spectra reported by other researchers [25]- [27], [32].…”

“…Typical literature spectra of ice are found e.g. in references [26]- [29], [32]- [33], [36], [38]- [40], [45]- [49]. We note that the ice peaks at positions around 3080-3160 cm -1 are depending on the temperature history of the sample.…”

“…There has been some discussion in the literature [25]- [36] about which bands really belong to the hydrohalite phase. Wise et al [33] have convincingly shown (in their Figures 7a and 7b [33]) that Raman bands at around ~3100 and 3160 cm -1 come from ice nucleated on hydrohalite particles, because these bands disappeared after the ice had disappeared by sublimation, whereas the other bands -due to hydrohalite -remained.…”

“…For example, the sixth-closest moon, Europa, orbiting around the planet Jupiter, has an estimated 9 km thick icy shell overlying an aqueous liquid mantle covering a salty subsurface ocean. This icy cover, and perhaps the liquid underneath and bottom deposits are estimated to contain gigantic amounts of hydrohalite [12], [36]. However, the current knowledge of Europa's subsurface ocean is sparse, and its eventual habitability is critically depending on e.g.…”

Crystal structures of NiSO4·9H2O and NiSO4·8H2O: magnetic properties, stability with respect to morenosite (NiSO4·7H2O), the solid-solution series (MgxNi1−x)SO4·9H2O

“…Since these environments are typically much colder than the Earth's mean surface temperature, the behaviour of such brines when crystallised at low temperatures-even flash frozen, as may occur on extrusion or spraying into the ultra-cold surface environment of an outer solar system body-is important to understand. This is reflected in the efforts of the planetary science community to determine experimentally which stable or metastable phases appear when different brine compositions are frozen at different rates (e.g., Hennings et al 2013;Schmidt et al 2013;Toner et al 2014;Vu et al 2016Vu et al , 2017Thomas et al 2017) or when salt hydrates are exposed to elevated relative humidities at low temperatures (Leftwich et al 2013). Our work on divalent metal sulfate cryohydrates adds a small piece to this larger picture.…”