Space weathering simulation of micrometeorite bombardment on silicates and their mixture for space application

Abstract

Missions to planetary bodies require innovative techniques for the in situ investigation of their surfaces, especially when landings are planned. Therefore, Raman spectroscopy as an excellent laboratory tool for rapid mineralogical analysis of both terrestrial and extraterrestrial rocks has been successfully proposed for the investigation of planetary surfaces. Examples are the Raman laser spectrometer (RLS) of the joint ESA and Roscosmos mission ExoMars 2022 as well as Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) and SuperCam onboard NASA's Mars2020 Perseverance Rover; another is the Raman spectrometer for Martian Moons eXploration (MMX) (RAX), which is being developed for the in situ exploration of the Mars' moon Phobos. When preparing such space missions, it is essential to be prepared for all possible outcomes, such as samples exhibiting space weathering (SW). In this work, we study the influence of micrometeorite bombardment on bodies without atmosphere as one trigger of SW. This type of SW effect is simulated with an excimer laser irradiating the investigated samples with an energy density of ~2.5 J/cm2 for each pulse. As possible components on Phobos, we investigated the silicates olivine (Fo91) and pyroxene (En87) and their mixtures with Raman spectroscopy before and after laser irradiation. Surprisingly, the characteristic Raman bands of the individual minerals in the spectra are not influenced by this kind of SW. On the other hand, the fluorescence-dominated background signal induced by laser irradiation is reduced, possibly due to the formation of nanophase Fe, which then facilitates a better interpretation of the individual mineral peaks.