Laboratory exploration of mineral precipitates from Europa's subsurface ocean

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.

A Review on Hypothesized Metabolic Pathways on Europa and Enceladus: Space-Flight Detection Considerations

“…Metabolic processes in life as we know it have only generally been detected at above −20 °C, and life usually becomes dormant at lower temperatures. This is very close to the theorized temperatures of the Europan ocean, which would be close to freezing, though Thompson et al [ 37 ] predict the salinity will probably reduce these temperatures to around 250 K (~−23.15 °C). Some authors have theorized that psychrophiles that are halotolerant might be able to persist on Europa in the saline subsurface oceans [ 82 ].…”

“…Enceladus Europa pH Basic (8-11) [27,28] Most likely acidic (~4-6), but not well constrained [29,30] Pressure 1.5-10 MPa [31,32] 110-260 MPa [30,33,34] Ice shell thickness 5-25 km (excluding south pole terrain) [31,35,36] 5-100 km [37][38][39] Notable species H 2 , CO 2 , NH 3 , CH…”

“…Icy/ocean worlds like Europa that formed in the outer solar system are thought to be more volatile-rich than the planetary bodies in the inner solar system [ 51 ] Europa’s structure is made up of an archetypical layered ice shell with a rigid, stagnant lid which overlies a convecting ice mantle that has active tectonism [ 52 ]. Europa’s ice shell thickness has been debated but is believed to be between ~5–100 km ( Table 1 , [ 37 , 38 , 39 ]) with a ~100 km deep ocean based on analysis of tidal heating, subduction, dissipation, and conductive cooling, e.g., [ 17 , 52 , 53 ]. There is limited evidence that water plumes may be currently erupting from Europa’s surface, allowing for a possible future opportunity to collect the ocean material and study it from space (e.g., [ 54 , 55 , 56 ]).…”

“…Ocean temperatures for Europa should lie close to freezing; however, salinity effects could reduce the temperatures to 250 K [ 37 ]. Moreover, despite the ocean being 100 km deep, the sea-floor pressure has been predicted to be 130–360 MPa [ 33 , 34 ] and more recently as low as 110 MPa because Europa’s gravity is less than one-seventh of Earth’s [ 37 ]. These pressures and temperatures dictate that the inorganic carbon stays in dissolved form [ 45 ].…”