A slow-cooling-rate in situ cell for long-duration studies of mineral precipitation in cold aqueous environments on Earth and other planetary bodies

Abstract

A sample environment cell for long-duration X-ray diffraction studies of mineral precipitation in very slow cooling aqueous environments on Earth and other planetary bodies is described. The results are reported of a year-long commissioning experiment monitoring the dynamics of a freezing MgSO4–H2O solution at −28°C (245 K) in which meridianiite and epsomite are observed to form.

Laboratory exploration of mineral precipitates from Europa's subsurface ocean

“…Qualitatively, the contribution of MS7 to the scattered intensity did appear, in general, to be reduced once MS11 had formed, consistent with the prediction that MS7 is replaced by MS11 (Kargel et al, 2000). In our previous study of an MgSO 4 -H 2 O system using this sample cell (Thompson et al, 2018), we similarly observed a slowly changing MS7/MS11 ratio and found that fits could be improved by the inclusion of an amorphous sulfate component to better model the background scatter. In addition, the strength of the background signal showed a steep rise below 250 K, which from the pattern of the diffuse scatter in the original area detector images was attributed to amorphous ice.…”

“…Its operating energy is 25 keV (0.49388 Å , calibrated average for the experimental run), to provide cell/ sample penetration, and detection is by area detector (Pixium), with 2D patterns obtained by integration around the image centre point. The LDE facility was used to house a cold cell designed for studies of hydrated mineral precipitation from slowly cooled aqueous solutions (Thompson et al, 2018) (see also Section 2.2.2 below).…”

“…Simple thresholding produced variable results such as halo artefacts, missed spots and loss of legitimate signals. Instead, as discussed by Thompson et al (2018), the images were first integrated into separate 1D data files and visually inspected. Those showing broad and intense non-background features were rejected (typically 1-2 images per week), while the remaining data were averaged to produce a single data file for each week.…”

“…Many of the icy objects in the outer Solar System are believed to harbour liquid oceans, as suggested variously by observation, modelling or plausible circumstance [see e.g. reviews by Hussmann et al (2006), Massé et al (2014) and Nimmo & Pappalardo (2016); see also Table 1 of Thompson et al (2018)]. Some of these will be in direct contact with their rocky cores.…”

“…This probably formed by residual water, with reduced salinity resulting from the precipitation of the salt, undergoing rapid freezing [see Fig. 8 of Thompson et al (2018) and the discussion in Sections 4.3 and 5.1 of that paper]. Fig.…”