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Abstract: A correlative multi-technique approach, including electron microscopy and X-ray synchrotron work, has been used to obtain both structural and compositional information of a sulfur-bearing serpentine identified in several carbonaceous chondrites (Winchcombe CM2, Aguas Zarcas CM2, Ivuna CI, and Orgueil CI), and in Ryugu samples returned by the Hayabusa2 mission. S-K edge X-ray absorption spectroscopy was used to determine the oxidation state of sulfur in the serpentine in all samples except Ryugu. The abundance of this phase varies across these samples, with the largest amount in Winchcombe; ~12 vol% of phyllosilicates are identified as sulfur-bearing serpentine characterized by ~10 wt% SO3 equivalent. HRTEM studies reveal a d001-spacing range of 0.64–0.70 nm across all sulfur-bearing serpentine sites, averaging 0.68 nm, characteristic of serpentine. Sulfur-serpentine has variable S6+/ΣStotal values and different sulfur species dependent on specimen type, with CM sulfur-bearing serpentine having values of 0.1–0.2 and S2− as the dominant valency, and CIs having values of 0.9–1.0 with S6+ as the dominant valency. We suggest sulfur is structurally incorporated into serpentine as SH− partially replacing OH−, and trapped as SO42− ions, with an approximate mineral formula of (Mg Fe2+ Fe3+ Al)2-3(Si Al)2O5(OH)5-6(HS−)1-2(SO4)2−0.1-0.7. We conclude that much of the material identified in previous studies of carbonaceous chondrites as TCI-like or PCPs could be sulfur-bearing serpentine. The relatively high abundance of sulfur-bearing serpentine suggests that incorporation of sulfur into this phase was a significant part of the S-cycle in the early Solar System.

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Abstract: Transition metals, including Iridium, are crucial for understanding planetary cores and developing critical technologies due to their unique properties under extreme high-pressure and high-temperature conditions. Although Ir’s room-temperature phase remains stable, its pressure-temperature phase diagram is largely unknown, with only a single experimental melting point reported previously. A notable gap in knowledge is the lack of experimental evidence for solid-solid phase transitions predicted by theoretical models. Here we show a new investigation into the phase diagram of iridium, employing a combination of resistive-heated and laser-heated diamond anvil cells coupled with synchrotron X-ray diffraction. Our findings confirm that Ir maintains its face-centered cubic structure up to 101 GPa and 5600 K. We determined five new melting points that corroborate computational predictions, providing a more robust foundation for the melting curve. The resulting thermal equation of state offers a definitive dataset that can serve as a reliable pressure standard and advance the design of technologies using Ir.

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Abstract: A challenge in sample return missions to restricted bodies such as Mars, Europa, and Enceladus is enabling mineralogical and geochemical analyses whilst maintaining cleanliness and containment. Notably, due to the potential for back-contamination of Earth from possible extant life on these bodies, strict contamination control measures must be taken for the purposes of planetary protection [1]. These measures restrict how analyses can be performed on the samples until they have been sterilised or judged safe. As the first step of scientific analysis for Mars Sample Return (MSR), for example, sealed samples would undergo a set of measurements called Pre-Basic Characterisation, or Pre-BC [2]. These data would be used to inform tube opening and decide experimental plans for subsequent multi-instrument analyses. Pre-BC includes X-ray CT and magnetic measurements but X-ray Diffraction (XRD) for identification and quantification of crystalline mineral phases is currently only planned for a later phase, due to the need for sample powdering to achieve sufficient diffraction signal using a conventional laboratory diffractometer.XRD using a synchrotron source enables sampling of sealed MSR sample tubes, but tubes must be kept in containment throughout transport and measurements. We have developed a prototype container at Space Park Leicester that can be used to take unopened drill tubes in a Sample Receiving Facility to a synchrotron beamline such as Diamond Light Source's I12 and perform XRD analysis whilst maintaining containment.Figure 1: MSR sample tube container for synchrotron XRD.MethodThe sample container used stainless steel construction in accordance with the permissible materials list for MSR samples. Remotely operated, low-offgassing motorised stages were used to position the sample tube and rotate it for spatial averaging. The windows were made out of fused silica, with a 30 mm diameter, 1 mm thick inlet window, and 100 mm diameter, 2 mm thick outlet.Synchrotron powder XRD measurements were taken at the I12-JEEP beamline at Diamond Light Source. The diffraction methodology was similar to our previous study [3] at I12 in which a basaltic sediment from Þórisjökull, Iceland collected as an MSR analogue through the SAND-E program [4] in just a Ti sample tube analogue was analysed as a feasibility test. The only differences were a 56.59 keV X-ray energy and a 1224.7 mm sample-to-detector distance. Four samples were measured: a solid basalt core from Skye, UK; an Old Red Sandstone core from Pembrokeshire, UK; the Icelandic regolith analogue mentioned previously; and mudstone fragments from Watchet, UK. The last two are official Jezero Crater Mars analogues. Sample analogues inside sample tubes were placed inside the container and diffraction measurements were performed through the windows. An empty tube was also measured as reference.Semi-quantitative analysis was used to identify the mineral phases present and roughly estimate their quantity, shown for the Icelandic sediment in Fig. 2. Diffraction patterns had the window and tube background subtracted after intensity scaling to enable this analysis as in Adam et al. [3], though this method is imperfect. Rietveld refinement is in progress for more accurate phase quantification.ResultsThe expected three constituent minerals, plagioclase, pyroxene, olivine, could still be identified, though with differences in atomic site occupancy for two of the phases (andesine, diopside, and larnite compared to the expected anorthite, diopside, and forsterite). The Figure of Merit of the phase matches was reduced: from 0.792, 0.783, and 0.764 for plagioclase, pyroxene, and olivine respectively, to 0.710, 0.670, and 0.705. Estimated quantity also changed from 42.3%, 34.5% and 23.2%, to 34.5%, 25.9% and 39.6%, respectively, though precise quantification is not expected from this semi-quantitative approach and will come from Rietveld refinement.

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Abstract: Pre-Basic and Basic Characterisation (BC) are a set of non-contact measurements to identify the basic physical and geological characteristics of returned samples from the joint ESA-NASA Mars Sample Return (MSR) campaign in order to inform its later, detailed analysis. They will be performed on all returned samples. Strict contamination control measures must be taken for planetary protection and to prevent contamination of the samples by Earth’s environment, so Pre-BC and BC will be carried out under high containment, which poses technical challenges. This work investigates X-ray Computed Tomography (CT) and synchrotron X-ray Diffraction (XRD) for the Pre-BC phase, and optical imaging for BC. Analogues for returned Mars2020 samples and the sample tubes were prepared. A BC visible light imager was developed which meet a proposed set of BC minimum measurement requirements. The imager’s spatial resolution and other image quality characteristics were measured and test BC of sample analogues performed, which confirmed that an imager with equivalent zoom range, spatial resolution, and field of view can successfully carry out BC. The required operating conditions for BC using micro-CT have been defined using a Nikon XTH225 microtomography scanner. Sample analogues were scanned inside and outside sample tube analogues, and BC requirements exceeded. Features such as grain size and porosity could be measured down to the scale of very fine sand (~60 μm). Powder XRD on sample analogues inside and outside sample tubes was tested using Diamond Light Source’s I12 beamline in order to determine whether this technique could be incorporated into Pre-BC. It was found that identification and quantification of the mineralogy of sealed Mars sample tubes was feasible, and the effect of the tube walls on analysis was small. Recommendations for future experiments to address observed challenges with BC instrumentation are made, and next steps to develop final BC instruments described.

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Abstract: Various icy moons, such as Europa and Ganymede, have thin oxygen atmospheres and exhibit spectral features attributed to oxygen held in their surface ices. The oxygen forms from the radiolysis of water. The interiors of these bodies are subject to high pressures and it is not known how deep into icy moons oxygen-bearing ices can penetrate, or the structures formed by the oxygen–water system at high pressure. Here, we show that oxygen hydrates are stable to 2.6 GPa, allowing them to penetrate deep into icy moons, both above and below proposed sub-surface liquid-water oceans. Similarities between oxygen and hydrogen hydrates indicate potentially enhanced recombination rates, transforming them back into water and offering a resolution to the discrepancy between predicted and measured radiolysis rates. In addition to the low-pressure CS-II clathrate, our results find three high-pressure phases in the oxygen–water system: an ST clathrate, a C0 hydrate, and a filled ice isomorphous with methane hydrate III. This shows a vast storage potential for molecular oxygen in icy moons and indicates that Europa could still be absorbing oxygen into its crustal ice.