Quantitative Analysis of the Variability in Spectral Characteristics of MgSO4 and Na2SO4 Brine Solutions for Europa Surface Comparative Analysis
Friday, 19 December 2014
Observations by the NIMS instrument (Near Infrared Mapping Spectrometer) on the Galileo orbiting spacecraft indicate the surface of Europa is largely dominated by water ice and frost. The dark terrain of Europa is likely to also have highly hydrated salts such as magnesium and sodium sulfate. Various hydration states of these compounds have previously been investigated and spectrally characterized. However, frozen brine solutions, which could more directly represent the subsurface ocean composition, have been largely neglected in these studies. Where frozen brine salts have been considered, changes in their reflectance spectra have not been well characterized with respect to changes in concentration, temperature and grain size. We present a quantitative comparison of spectral reflectance changes (0.35-10 µm) of magnesium and sodium sulfate brines with respect to changes in concentration (0%, 1%, 10%, and saturated solutions in water), temperature (100K, 175K, and 250K), and grain size (5 µm to 200µm). We have also developed a novel technique to simulate very fine grain brine frost that could represent emplaced material on the surface by ejection from plumes. This plume material could have physical properties and composition unique from other regions, providing spectroscopic evidence that is diagnostic of surface activity. Our analysis has shown that the spectral features of the frozen brines are grain size dependent, most noticeably near 3.0µm. We intend to use this grain size dependent spectral feature as a diagnostic tool for comparative analysis of surface spectra and visual imaging of geological features. The implications of this research will allow for a better understanding and validation of theories regarding geological morphology, more precise linear mixture modeling for the determination of exact surface composition, and improved inputs for precipitation and fractional crystallization models of ocean content and ocean concentrations.