LIBS studies of ferric salts in frozen solutions under Martian conditions

Abstract

Laser-induced breakdown spectroscopy (LIBS) is a promising analytical tool for the geochemical investigation of surfaces and soil in particular for extraterrestrial exploration. With the ChemCam instrument on the NASA Mars Science Laboratory (MSL), which will arrive on Mars in summer 2012, the LIBS technique will be applied for in-situ analysis on a planetary mission for the first time. Additionally other missions with LIBS are proposed for instance for Venus or the Moon. To optimize the scientific return with LIBS, i.e. to most precisely obtain the elemental composition of rock, soil and possibly frozen samples with LIBS, qualitative and quantitative methods for data analysis have been developed and improved by a number of studies. One valuable attempt to compensate for matrix effects and other factors that influence the plasma’s composition and properties and therefore the LIBS spectra are multivariate analysis (MVA) methods. This study investigates the potential of LIBS for dentifying ferric salts (FeCl3 and Fe2(SO4)3) when pressed into pellets and in frozen salt solutions utilizing partial least squares discriminant analysis (PLS-DA). Ferric salts are considered in the context of possibly existing liquid brines on Mars and are moreover of particular interest for (astro-) biology in view of possible extraterrestrial life since iron is an essential component of life as we know it. Ferric sulfates have been found on Mars at various locations such as jarosite in Meridiani Planum and in soils in Gusev Crater. Chloride bearing salts were also identified in deposits on the southern hemisphere. On Mars these salts could also appear in form of frozen salt solutions which can be investigated using the LIBS technique as shown previously.