Laboratory exploration of mineral precipitates from Europa's subsurface ocean.

Stephen P Thompson,Hilary Kennedy,Sarah J Day,Aneurin Evans,Benjamin M Butler,Emmal Safi

doi:10.1107/s1600576721008554

Abstract

The precipitation of hydrated phases from a chondrite-like Na-Mg-Ca-SO4-Cl solution is studied using in situ synchrotron X-ray powder diffraction, under rapid- (360 K h-1, T = 250-80 K, t = 3 h) and ultra-slow-freezing (0.3 K day-1, T= 273-245 K, t = 242 days) conditions. The precipitation sequence under slow cooling initially follows the predictions of equilibrium thermodynamics models. However, after ∼50 days at 245 K, the formation of the highly hydrated sulfate phase Na2Mg(SO4)2·16H2O, a relatively recent discovery in the Na2Mg(SO4)2-H2O system, was observed. Rapid freezing, on the other hand, produced an assemblage of multiple phases which formed within a very short timescale (≤4 min, ΔT = 2 K) and, although remaining present throughout, varied in their relative proportions with decreasing temperature. Mirabilite and meridianiite were the major phases, with pentahydrite, epsomite, hydrohalite, gypsum, blödite, konyaite and loweite also observed. Na2Mg(SO4)2·16H2O was again found to be present and increased in proportion relative to other phases as the temperature decreased. The results are discussed in relation to possible implications for life on Europa and application to other icy ocean worlds.

Highlights

Jupiter is the largest planet in the Solar System and has 79 currently identified moons
NMS16 was first reported by Leftwich et al (2013) as a lowtemperature phase derived by chance from deliquesced NMS4 held below 283 K for up to ten days in a freezer, its structure being solved using single-crystal X-ray diffraction
Subsequent attempts to form NMS16 resulted, 20–30% of the time, in a mixture of the single-cation phases NS10 and either MS11 or MS7, depending on the relative humidity and temperature conditions, suggesting that NMS16 was not thermodynamically stable

Summary

Introduction

Jupiter is the largest planet in the Solar System and has 79 currently identified moons (https://solarsystem.nasa.gov/ moons/jupiter-moons/overview). The four are known collectively as the Galilean moons, after Galileo Galilei who, in 1610, was the first both to observe them and to recognize that they were satellites to another planet. Despite these early observations, the existence of a global ocean of liquid water beneath an icy surface is a relatively recent discovery. Images from the Voyager missions of the 1970s revealed a surface with relatively few craters, indicative of recurrent global resurfacing Both Voyager and the later 1990s Galileo mission showed the surface of Europa to be smooth and crisscrossed by extensive intersecting fractures (Fig. 1), along with other surface structures with diverse morphologies (Pappalardo et al, 1999).

Results

Discussion

Conclusion