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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - RESOLVE (Reconstructing the History of Lunar Volatiles)

Teaser

Summary

The problem:

Project RESOLVE (Reconstructing the History of Lunar Volatiles) aims at understanding how the abundance and the distribution of water and its isotopic composition is influenced by the crystal structure of the host mineral apatite in lunar rocks. Apatite, like any other mineral, responds to pressure increase caused by the impact events by accommodating i.e. compressing their crystal structures, causing redistribution of the volatile, but also of the stable (e.g., H, Cl) and radiogenic isotopes (e.g., Pb). Therefore they not only provide a unique opportunity for precise age-determination of an impact event, but also simultaneous determination of the isotopic composition of the water, that is a fingerprint to its source. In that way we can learn when did water enter apatite and what was the source of that water. This takes us further to understand if water on Moon and Earth share the common origin.

The importance for society:

RESOLVE was presented at the meetings where planning of future space missions took place. These meeting included, but were not restricted to the annual European Lunar Symposium (ELS) and the UK-Node of NASA SSERVI (Solar System Exploration Research Virtual Institute), where many members of various international space agencies (ESA, NASA and JAXA) definition teams responsible for planning of the future lunar missions were present, too. On the other hand, through the well-established collaboration of the OU and Natural History Museum (NHM, London), RESOLVE was exposed to the on-going planning and development of curation facilities in the scope of the future Sample Return Missions in Europe and internationally (e.g. Hayabusa 2 asteroid sample return, Lunar Polar Sample Return, Bennu asteroid by OsirisREX mission).The strong collaborative nature of RESOLVE advanced the quality of European science, augmenting and facilitating more intensive collaboration with colleagues in North America, Canada and Australia.

WPs and Objectives:
We applied a multi-disciplinary approach by combining in situ elemental, stable and radiogenic isotope geochemistry with structural characterization of the apatite in order to investigate how geological processes, primarily impacts, affect distribution of water in lunar rocks. This was achieved through four different work packages (WPs) that corresponded to four different objectives (see below).

Work performed

The main analytical techniques proposed included Scanning Electron Microscopy (SEM), Cathodoluminescence (CL), Electron Microprobe Analysis (EPMA), Secondary Ion Mass Spectrometry (NanoSIMS), Electron Backscatter Diffraction (EBSD) and U-Pb & Pb-Pb dating (SIMS). During the course of fellowship, however, the work was extended to include a pilot study applying Atom Probe Tomography (APT) and Transmission Electron Microscopy (TEM). The O4 covered numerous outreach and result dissemination activities throughout the fellowship.
We investigated H2O content and D/H isotopic composition (O1) in zoned magmatic apatite in unshocked low-Ti lunar basalt and in (O2) apatite from shocked lunar highland rocks. Further on, we investigated the crystallization and/or impact ages by analysing U and Pb isotopes of apatites and other associated minerals (merrillite, baddeleyite) from highland lunar lithologies that display a range of shock effects (O3). These objectives were reached by intense national and international collaboration with the University of Portsmouth (UK), Curtin University (Perth, Australia), and Swedish National Museum in Stockholm (Sweden). Results achieved in RESOLVE are of very high-quality and novelty, and were presented at many conferences (Muenster, Toulouse, New Orleans, Houston), workshops (Perth), public events in the UK, seminars, publications, media, etc. The outreach event â€™â€™Moon Nightâ€™â€™ organized at the OU engaged local school children and showed them the wonders of lunar research. Participants had a chance to see the European Astronaut training facility (Cologne) in a live telecon. Another well-received activity that originated through RESOLVE was an international workshop in â€˜â€™Geology and Geophysics of the Solar Systemâ€˜â€™, first of its kind to be organized in the Balkans and that is now set to run every two years.

Final results

The seven most important finidgs of RESOLVE
1) Apatite microtexture is an indicator of shock-load and can be quantified with increasing stages of deformation; 2) apatite within distinct petrological types of lunar highland samples, contains from 10 to 2000 ppm H2O, regardless of their shock-deformation stage; 3) apatite crystallized from the impact melt is not water-depleted; 4) apatite is a reliable hygrometer: water isotopic composition in apatite does not seem affected by the apatite microtexture. However, water-poor apatite grains from heavily shocked rocks show low-Î´D values implying possible contribution of the regolith (D-poor) material. 5) Highly-shocked apatite is not amorphous but rather nano-crystalline, as revealed by APT and TEM. Nano-crystalline apatite is one of the most-stable mineral analysed by APT so far; 6) Apatite is found to be a sensitive impact-geochronometer, with its U-Pb and Pb-Pb ages easily reset at all shock stages. 7) There is an evidence for intense lunar surface bombardment ca. 500 million years before present, which coincides with an intense asteroid break-up event in the inner Solar System.