In-Situ Science on Phobos with the Raman spectrometer for MMX (RAX): Preliminary Design and Feasibility of Raman Measurements

Abstract Mineralogy is a key to understanding the origin of Phobos and its place in the context of the Solar System evolution. In-situ Raman spectroscopy on Phobos would be an important tool to achieve the science objectives of the Martian Moons eXploration (MMX) mission and maximize the science merit of sample return by characterizing the mineral composition and heterogeneity of the surface of Phobos. Conducting in-situ Raman spectroscopy under the harsh environment of Phobos requires a very sensitive, compact, lightweight, and robust Raman instrument that can be carried by the very compact MMX rover. In this context, a Raman spectrometer for MMX (RAX) is currently under development by an international collaboration between teams from Japan, Germany, and Spain. To demonstrate the capability of a compact Raman system like RAX, we built an instrument that reproduces most of the optical performance of the flight model using commercial off-the-shelf parts. Using this performance model, we measured mineral samples relevant to Phobos and Mars, such as anhydrous silicates, carbonates, and hydrous minerals. Our measurements of these samples indicate that such minerals can be measured and identified with a RAX-like Raman spectrometer with sufficiently high accuracy. We demonstrated a spectral resolution of approximately 10 cm -1 and high sensitivity of the Raman peak measurements (e.g. signal-to-noise ratios up to several 100). These results strongly suggest that the RAX instrument will be capable of determining the minerals expected on the surface of Phobos, adding valuable information to address the question on the moon’s origin, heterogeneity, and circum-Mars material transport.