Quantification of Fluorescence Emission from Extraterrestrial Materials and Interference to Micro-beam Cw 532 Nm Raman Spectroscopy

Why meteorites? Meteorites and the samples returned by planetary missions supplied the extraterrestrial materials for human beings to study the solar system and beyond far away from Earth. They provide chemical and mineral compositions representing the planetary bodies in solar system, e.g., planets, satellites, asteroids, comets, and near-Earth objects. They can also serve for testing instruments for planetary exploration. Three Raman systems have been selected for two landed missions on Mars (ExoMars 2018 and Mars 2020). Because of its capability of providing definitive molecular (organic and inorganic) identification and characterization, planetary Raman spectroscopy is anticipated to use for many more future missions to planets and small bodies. In terrestrial geological applications of Raman spectroscopy, one of the major limitations comes from possible fluorescence interference from the analyzed samples. The fluorescence emission can be produced from bio-genetic species that were trapped in porous rocks or soils (e.g., clays). They can also be generated from the electronic transition modes of rare earth elements (e.g., REE–enriched minerals), or in some cases from transition metals. Knowledge about fluorescence emission from extraterrestrial materials and how much it will interfere with planetary Raman spectroscopy in exploration will help in selecting the best Raman instrument configuration for a mission. For this study, we used a broad range of meteorites, with their categories cover 97% of all types of stony meteorites fallen on Earth, to mimic the potential fluorescence threat to a micro-beam cw 532 nm Raman system (MMRS/CIRS, with the simplest configuration and highest TRL) that we have been developing for planetary missions, supported by PIDDP, MIDP, ASTEP, and MatISSE programs.