Raman spectra of hydrous minerals investigated under various environmental conditions in preparation for planetary space missions

Abstract

Raman spectrometers will be part of the scientific payload of the future lander missions to Mars, icy moons, and asteroids. Their primary task is the search for life including the detailed characterization of the planetary environment. H2O/OH−‐ bearing minerals are essential for biological processes; thus, their Investigation will have a special focus. Cyclic temperature variations on planetary surfaces, for example, on Mars between 300 and 140 K from summer midday to winter night, induce re‐organization of the internal mineral structures, which can be monitored by Raman spectroscopy. Therefore, temperature dependent changes in Raman spectra under step‐wise cooling/re‐heating of typical planetary surface related H2O/OH−‐bearing minerals (e.g., carnallite, natrolite, gypsum, phlogopite, talc, and tremolite) are the focus of this work. Spectra were taken under space relevant simulated conditions, from vacuum and cryogenic temperature to room conditions, including those that resemble the Martian surface atmosphere. Special attention was dedicated to the typical vibrational stretching modes of H2O/OH−‐bearing minerals. H2O‐bearing minerals exhibit significantly different temperature related changes when compared to OH−‐bearing minerals. We observed the formation of an ice‐like Raman spectrum during step‐wise deep cooling of carnallite. Gypsum shows a blue shift of the H2O band with decreasing temperature. All other investigated minerals display no significant variations over the entire Raman relevant spectral range. The results of this study are be made available in a Raman database of the flight Raman instruments.