Raman spectroscopy using miniaturised spectrometers in preparation for the 2020 ExoMars rover mission

Over the past two decades, the potential of Raman spectroscopy as a tool for planetary exploration has been explored in detail and greatly advocated. It is ideally suited for in situ measurement as it provides rapid, non-destructive, unambiguous molecular identification, without any need for mechanical or chemical sample preparation. Developments in the miniaturisation of lasers, charge-coupled device detectors and other instrument components has, for the first time, enabled the development of Raman instruments for space missions. The first to be deployed on another planet will be the Raman Laser Spectrometer instrument onboard the ExoMars rover, a joint mission between the European Space Agency and the Roscosmos State Corporation for Space Activities, which will be launched in 2020. Two further Raman instruments, SuperCam and SHERLOC, will be included in the payload of NASA’s Mars 2020 rover. Prior to the deployment of these instruments, it is necessary to conduct analogue studies using flight-representative hardware in order to optimise instrument configuration, mode of operation, data extraction and analysis protocols. The programme of research presented in this thesis constitutes a series of such studies. The capabilities of two flight-representative, portable Raman spectrometers, one using 532 nm excitation and the other 785 nm, have been evaluated through a series of Mars analogue studies. Spectra have been acquired from a range of relevant target materials, including silica, haematite and calcium sulphate of varying levels of hydration. Caution is urged in the interpretation of spectra from portable Raman systems, since limitations introduced by their miniaturisation make band misassignment possible. As a result of this research, it is recommended that instruments are designed with a minimum spectral range from 100 to 4000 cm-1 and a spectral resolution of at least 3 cm-1, in order to avoid the misinterpretation of spectra. Several sets of analogue samples that are rich in reduced carbon have also been studied. It has been demonstrated that reduced carbon can not only be detected in concentrations as low as 0.08%, but distinct carbon populations can be differentiated by the measurement of certain spectral parameters. Furthermore, this analysis enables the qualitative comparison of the thermal maturity of different samples containing reduced carbon. These analytical techniques will be highly valuable when analysing spectra returned by planetary instruments.