Thermal and radiation stability of the hydrated salt minerals epsomite, mirabilite, and natron under Europa environmental conditions

Abstract

Abstract. We report studies on the thermal and radiolytic stability of the hydrated salt minerals epsomite (MgSO4o7H20), mirabilite (Na2SO4 ß 10H20 ), and natron (Na2CO3 ß 10H20 ) under the low-temperature and ultrahigh vacuum conditions characteristic of the surface of the Galilean satellite Europa. We prepared samples, ran temperature-programmed dehydration (TPD) profiles and irradiated the samples with electrons. The TPD profiles are fit using Arrhenius-type first-order desorption kinetics. This analysis yields activation energies of 0.90+0.10, 0.70+0.07, and 0.45_+0.05 eV for removal of the hydration water for epsomite, natron, and mirabilite, respectively. A simple extrapolation indicates that at Europa surface temperatures (_<130 K), epsomite should remain hydrated over geologic timescales (-1011-10 TM years), whereas natron and mirabilite may dehydrate appreciably in approximately 108 and 103 years, respectively. A small amount of SO 2 was detected during and after 100 eV electron-beam irradiation of dehydrated epsomite and mirabilite samples, whereas products such as 0 2 remained below detection limits. The upper limit for the 100 eV electron-induced damage cross section of mirabilite and epsomite is -10 -19 cm 2. The overall radiolytic stability of these minerals is partially due to (1) the multiply charged nature of the sulfate anion, (2) the low probability of reversing the attractive Madelung (mostly the attractive electrostatic) potential via Auger decay, and (3) solid-state caging effects. Our laboratory results on the thermal and radiolytic stabilities of these salt minerals indicate that hydrated magnesium sulfate and perhaps other salts could exist for geologic timescales on the surface of Europa. [1998, 1999a] proposed from the NIMS spectroscopic evidence that these absorptions were due to hydrated (and not just hydroxylated) minerals, with the most likely candidate matehals being

Spectral comparison of heavily hydrated salts with disrupted terrains on Europa

“…The shapes of the distorted absorption features in the near-IR observations of Europa certainly resemble those seen in the spectra of many hydrated materials characterized in laboratory studies thus far (Crowley, 1991;Dalton and Clark, 1998;Carlson et al, 1999bCarlson et al, , 2005McCord et al, 2001McCord et al, , 2002Dalton, 2000Dalton, , 2003. In addition, the presence of hydrated salts is consistent with hypothesized geochemical formation processes (Kargel, 1991(Kargel, , 1998Fanale et al, 1998Fanale et al, , 2001Kargel et al, 2000;Zolotov and Shock, 2001).…”

Europa's Sodium Atmosphere: An Ocean Source?

“…This is not surprising for a number of reasons. First, if the sodium exists as a sulfate or carbonate, it is in a hydrated form which is less refractory (McCord et al 2001). More importantly, a large fraction of the sputtered sodium returns to the surface and is adsorbed in icy regions.…”

Extensive water ice within Ceres’ aqueously altered regolith: Evidence from nuclear spectroscopy

“…Surficial water ice was not detected in Ceres' global regolith (5). However, it is conceivable that exposure of clays, hydrated salt and hydroxides to water vapor over geologic timescales may result in accumulation of adsorbed water within the regolith (77). Carbonaceous chondrites contain organic material with a molar H/C ratio of 0.7 (19).…”