In situ science on Phobos with the Raman spectrometer for MMX (RAX): preliminary design and feasibility of Raman measurements

Abstract

Mineralogy is the key to understanding the origin of Phobos and its position in the evolution of the Solar System. In situ Raman spectroscopy on Phobos is an important tool to achieve the scientific objectives of the Martian Moons eXploration (MMX) mission, and maximize the scientific merit of the sample return by characterizing the mineral composition and heterogeneity of the surface of Phobos. Conducting in situ Raman spectroscopy in the harsh environment of Phobos requires a very sensitive, compact, lightweight, and robust instrument that can be carried by the compact MMX rover. In this context, the Raman spectrometer for MMX (i.e., RAX) is currently under development via international collaboration between teams from Japan, Germany, and Spain. To demonstrate the capability of a compact Raman system such as RAX, we built an instrument that reproduces 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 indicate that such minerals can be accurately identified using a RAX-like Raman spectrometer. We demonstrated a spectral resolution of approximately 10 cm−1, high enough to resolve the strongest olivine Raman bands at ~ 820 and ~ 850 cm−1, with highly sensitive Raman peak measurements (e.g., signal-to-noise ratios up to 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 of the moon’s origin, heterogeneity, and circum-Mars material transport. Graphical Abstract

ORIGO: A mission concept to challenge planetesimal formation theories

“…The RLIBS has significant space heritage. This includes ChemCam (only LIBS) aboard Curiosity Rover (Fabre et al, 2011), SuperCam aboard Perseverence Rover (Manrique et al, 2020), ExoMars RLS (Raman only; Veneranda et al, 2021), and RAX -the small Raman spectrometer developed for MMX Rover (Cho et al, 2021). The same is true for the LAMS, which has heritage from the Phobos-Grunt Mission (Managadze et al, 2010) and Luna-Glob (Chumikov et al, 2021).…”

Martian moons exploration MMX: sample return mission to Phobos elucidating formation processes of habitable planets

“…The rover will be released before the landing operation and conduct an in situ examination of the Phobos surface. The rover powered by its solar generator will be equipped with navigation cameras, wheels for travel with torque sensors, wheel cameras, imaging the interaction of the wheels with the regolith, a thermal radiation monitor (MiniRad), accelerometers characterizing impact and bouncing, and a laser Raman microscope, RAX (Cho et al 2021). These instruments will examine mechanical, dynamical, and thermal properties and mineralogy of Phobos surface regolith.…”

The MMX rover: performing in situ surface investigations on Phobos

“…In addition to characterizing the physical properties of the surface material on Phobos, the rover will also measure its mineralogical composition by Raman spectroscopy (Cho et al 2021). Measuring the composition at various spots (possibly even of various individual grains) along the rover path gives ground truth measurements, but also characterizes the heterogeneity of the regolith, providing important context information for the returned samples.…”

“…3) is a compact, low-mass instrument with a volume of approximately 81 × 98 × 125 mm 3 and a mass of less than 1.4 kg. RAX was developed by DLR, INTA/UVA and JAXA/ UTOPS/Rikkyo (for more information see Cho et al (2021), this issue). It is designed to withstand the harsh conditions on Phobos and will be the first Raman spectrometer on an airless body.…”