Search

The joint NASA‐ESA Mars sample return campaign aims to return up to 31 sample tubes containing drilled sedimentary and igneous cores and regolith. The titanium alloy tubes will initially still be sealed when they are retrieved. Several types of measurement will be carried out on sealed samples in the pre‐basic characterization phase of scientific investigation. We show that powder x‐ray diffraction (XRD) analysis can be successfully carried out on sealed samples using an x‐ray source at the I12 beamline of Diamond Light Source synchrotron. Our experiment used an analog sample tube and a Martian regolith analog (Icelandic basaltic sand). The titanium walls of the tube analog give strong but few diffraction peaks, making identification of the major constituent mineral phases feasible. A more significant constraint on quantification of mineral phase abundances by this XRD technique is likely to be the grain size of the sample. This technique opens up the possibility of initial mineralogical analysis of samples returned from Jezero crater without opening the sample tubes and the potential changes to the sample that entails. [ABSTRACT FROM AUTHOR]

Introduction: The Askival sample is a geochemically and texturally unique sample investigated by the Curiosity rover in Gale crater. Located at the Bressay site and analyzed between mission sols 2015 to 2021, Askival has a feldspathic cumulate texture, but presents geochemical evidence of aqueous alteration beyond initial crystallization and accumulation. An earlier target, Bindi, provides an important comparative sample as it also appears to be a feldspathic cumulate but lacks the alteration present in Askival. Methods: Geochemical analysis of Askival and Bindi was performed using the Chemistry and Camera (Chem-Cam) instrument on the MSL Curiosity rover [1]. ChemCam is a laser induced breakdown spectrometer (LIBS) instrument that performs geochemical remote sensing on targets up to 7 m away from the rover. LIBS analyses occur by creating an energized plasma at a micron-scale point on the target rock, allowing for sampling of different phases within coarse-grained targets such as Askival. Supporting imagery from the ChemCam remote micro-imager (RMI) allows these chemical analyses to be correlated with visual identification of different phases. Further geochemical analysis of Askival using the Alpha-Particle X-Ray Spectrometer (APXS) [2] and images from the Mars Hand Lens Imager (MAHLI) [3] provide complementary datasets. Results & Analysis: Texturally, Askival has strong resemblance to feldspar cumulate samples, with roughly 65% of the sample consisting of light-toned, subhedral crystals with some examples of elongation. This phase is separated and, in some cases, enclosed by a fine-grained darker matrix, which comprises approximately 30% of the sample. The remaining texture is comprised of a fibrous grey/brown phase that occurs only in a couple of visible areas of the sample, as well as a secondary light-toned phase observed as small veins occupying interstitial areas. Geochemically, the primary light-toned phase has a range of compositions which form a linear trend away from stoichiometric feldspar composition. The most prominent chemical divergence is an enrichment in silica, with some of the sampled LIBS points containing >80% SiO2. This enrichment correlates with a detected increase in H, and a decrease in alkali elements and enrichment in Mg. This is consistent with the production of a leached layer and precipitation of secondary Mg-phyllosilicates under low temperature acidic conditions [4]. Other rocks located at Bressay do not show similar alteration, and are not of the same cumulate origin, indicating either a diversity of sources within a single locality or that Bressay has a collection of samples that have undergone different transportation pathways. The secondary phase presents a diverse mafic composition, indicating multiple mineral endmembers contributing to the phase that are not visibly distinguished in the RMI imagery. Normative calculations support a composition made of Fe/Mg silicates including pyroxenes and amphibole, supporting a model of formation under an upper crustal setting. [ABSTRACT FROM AUTHOR]