Technology Developments towards a Combined Xrd-xrf Instrument for Planetary Surface Analysis

Geochemical analysis of the surface material of terrestrial type planets is of fundamental importance in understanding the geological context of the planetary environment. Consequently this analysis should be performed whenever possible and indeed this has occurred on a number of previous landers. Current techniques include X-ray fluorescence (XRF) and Rutherford back-scattering of alpha particles, which provide information on the elemental composition of the sample. However, geological understanding can be greatly improved if the mineral structure of the sample can also be determined. The dominant method used for mineralogical identification of geological samples in earth-based laboratories is X-ray diffraction (XRD), which analyses the crystal lattice structure to decipher the constituent minerals. When XRD is combined with XRF it creates a powerful tool for characterisation of the geochemical, mineralogical and, by inference, the petrological nature of geologic material. To date no XRD instrument has been operated on the surface of another planet but a number of combined XRD – XRF instruments for planetary surface operation are currently under development in the US, Europe and Japan. In this paper we describe a number of technology developments that are taking place in the UK aimed at developing an efficient excitation and detection system for such a combined XRD-XRF instrument.