Use of miniaturized Raman spectrometer for detection of sulfates of different hydration states – Significance for Mars studies

• Miniaturized Raman spectrometers allow obtaining spectra of sulfates.
• Spectrometers tested represent tools of relevance for prototype preparation.
• The degree of hydration of Mg sulfates is related to the position of the ν1 band.

The presence of sulfates of different hydration states, specifically magnesium sulfates, has been firmly established on Mars from data acquired by both orbital and in-situ measurements. A lander mission typically involves a variety of instruments capable of performing a wide range of experiments from mineralogical tasks to the search for traces of life. It is clear from ongoing research that Raman spectroscopy can cover all of these tasks, and it has already been decided that future mission to Mars will employ a miniature Raman spectrometer. In this paper we report and discuss the Raman spectra of various sulfate minerals, with an emphasis on the magnesium sulfates. These were acquired by a hand-held Raman instrument, using the presently uncommon 532 nm excitation, the wavelength that is planned for the ESA lander mission. A sufficient quality of spectra were obtained with reasonably low spectral acquisition times, and the characteristic shift of the sulfate ν1 band in the MgSO4·n(H2O) minerals was confirmed. This was used for the unambiguous identification of magnesium sulfates of different hydration states. The present testing has confirmed the good performance of the handheld instrumentation for discrimination of structurally similar sulfates of relevance for Mars studies. This step has been proposed as the basis for subsequent testing of this instrumentation under Earth-based but Mars-analogous conditions, even using currently existing miniaturized Raman prototypes.