In situ search for life traces in extraterrestrial samples by synchrotron x-ray fluorescence 2D and 3D imaging

To set an optimal analytical strategy of the search for life traces, it is decisive to start their study in the preliminary examination stages of the extraterrestrial Returned Samples, once they are still stored in their original container. The relevance of the application of on-going synchrotron micro-X-ray fluorescence (XRF) methodological developments performed at the ID21/ID22 beamlines of the ESRF is critically examined in this paper. XRF computed tomography (XFCT) at ID22 is in general a precious tool allowing a non-invasive and non-destructive determination of the three-dimensional mineralogy of sub-millimeter silicate grains with micrometer resolution. A combination of absorption and Compton tomographies is a more promising method to image bulk views of the organic matter distribution. XRF-scanning X-ray microscopy (SXM) at 11321 is in general not adapted for studying samples across a container. However, it appears to be a unique tool to set up a list of the sub-surface sites where tiny amounts of organic matter are present. Adaptation of the SXM chamber to the quarantine criteria stipulated by the spatial agencies is a way to permit such analyses in the preliminary examination stages.