The comparative analytical performance of the Beagle 2 X-ray Spectrometer for in situ geochemical analysis on Mars

The Beagle 2 X-ray Spectrometer (B2 XRS) instrument was part of the Beagle 2 Mars lander payload and intended to perform in situ geochemical analyses of geological materials on Mars. The analytical performance of a spare version of the B2 XRS was compared with (1) a portable X-ray fluorescence (PXRF) spectrometer designed to perform terrestrial fieldwork and (2) a laboratory-based wavelength-dispersive (WD-XRF) system used to produce high quality geochemical data. The criteria used to assess the performance were based on fitting precision, accuracy and detection limit, determined from the analysis of international geochemical reference materials. The fitting precision of the B2 XRS and PXRF was found to be in agreement with the Horwitz function (a benchmark relating the analysed concentration of an analyte to its uncertainty) over 4 orders of magnitude of concentration range from 10(-1) to 10(-5) g/g. The PXRF generally had a better fitting precision than the B2 XRS because of its better resolution. In order of improving accuracy, the spectrometers generally are ranked B2 XRS, PXRF and WD-XRF for various major and trace elements. A limiting factor in the accuracy of the B2 XRS was the application of the algorithm used for its quantitative analysis. The detection limits for the spectrometers ranked in the same order as the accuracy as a result of improving signal-to-noise ratio (SNR) of elemental peaks, which is a direct consequence of improving resolution between these spectrometers. Overall, the B2 XRS was found to have a favourable analytical performance compared to the benchmark spectrometers, despite having met considerable design constraints and qualification tests as a planetary instrument. Copyright (C) 2009 John Wiley & Sons, Ltd.