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Investigating the formation and early evolution of the Moon with a combined experimental and analytical approach

Periodic Reporting for period 1 - MoonDiff (Investigating the formation and early evolution of the Moon with a combined experimental and analytical approach)

Reporting period: 2018-06-01 to 2020-05-31

"This project aims to provide vital analytical and experimental information that can be used to create models of how the Moon evolved and when it formed. In particular, the project builds on recent advances in determining the ages and compositions of volcanic rocks from the Moon. These new datasets have provided the basis for a preliminary model describing how the interior of the Moon evolved from global ""magma ocean"", into the planetary body that we see today. Ultimately, this model provides a new way to address the question of when the Moon formed. However, the model relies on understanding how radiogenic pairs of elements (for example U and Pb) would have behaved in the early Moon and other rocky planets. Currently, this behavior is poorly constrained. Therefore, a series of high pressure and high temperature experiments have been designed, which will simulate conditions in the ""magma ocean"" period of lunar history. The results of these experiments will then be used to generate new models for the evolution of the Moon and the time of lunar formation.

The importance of this project extends beyond simply lunar science. Firstly, because the Moon provides a more complete geologic record than the Earth (where atmospheric weathering and plate tectonics have erased the earliest terrestrial rocks) studies of lunar rocks have revolutionised more general models describing how rocky planets like the Earth formed. Analogously, this study will produce results that are not just relevant to lunar science, but also to geologic and planetary sciences as a whole, by placing new constraints on models of planetary evolution. Furthermore, the timing of lunar formation is specifically relevant to the Earth, as a giant impact of the type thought to have formed the Moon would have had catastrophic effects on the Earth and its early geologic evolution.

Given that the depletion of Pb in lunar rocks has previously been attributed to loss of volatile elements very early in the Moon’s history, this work will also provide new insight into the lunar volatile element budget. By understanding the potential effects of U and Pb partitioning during lunar core formation and magma ocean crystallisation, we will have clearer knowledge of how volatile depleted the Moon would have needed to be, in order to explain the Pb isotope data acquired from lunar samples. The topic of lunar volatiles has been subject to a surge of interest in the last decade, with multiple new studies being published in high-profile journals. It is also a subject with a clear interdisciplinary link to astrobiology, given that volatiles (and specifically water) are fundamental to life as we know it, so it is vital to understand the behaviour of volatile elements and compounds during the formation of planetary bodies.

Finally, the behaviour of elements during metal-silicate segregation that will be studied here is also important in the steelmaking industry, and the host institution has strong links with the R&D division of Tata Steel, who are interested in the behaviour of Pb in particular.

The key objectives of this project are as follows:

- continued analysis of lunar samples, resulting in the production of a complete set of ages and Pb isotopic compositions of the main types of basalts sampled during the Apollo missions
- completion of high-pressure/temperature experiments in order to better constrain silicate/melt partitioning behavior for a range of radiogenic parent-daughter pairs
- combining experimental and analytical datasets to produce a revised model for the Moon's early magmatic evolution, and place new constraints on the age of the Moon"
The primary focus of this project has been on the experiments being performed at the VU Amsterdam. To this end, the researcher has performed approximately 50 experiments. The data from these experiments are currently being processed and prepared for publication.

The researcher has also continued to collaborate with researchers at the Swedish Museum of Natural History, Stockholm, in order to obtain further analytical data from a range of lunar samples. This has involved several trips to work in the laboratory at the museum and has led directly to two first author publications for the researcher (plus additional manuscript which is in preparation for publication), as well multiple co-authored publications.

The researcher has presented their work at multiple conferences and workshops. This has included:
- 2018 European Space Agency/Chinese National Space Agency workshop in Amsterdam, Netherlands (Oral presentation)
- 2019 Lunar and Planetary Science Conference in Houston, Texas, USA (Oral presentation)
- 2019 European Lunar Symposium in Manchester, UK (Oral presentation)
- 2020 European Lunar Symposium [originally planned to take place in Padua, Italy, but adpated to virtual conference due to 2020 COVID-19 pandemic] (Oral presentation)

The researcher has also presented their work with invited seminar talks at:
- University of Münster, Germany
- University of British Columbia, Canada
"The published results of the project so far will, first and foremost, be of interest to the lunar and planetary science community. This work is already being used as the basis for continuing similar studies and future project proposals at the researcher's previous institution (the Swedish Museum of Natural History). Furthermore, the ages determined for Apollo samples are already helping to inform other scientists using remote sensing techniques to determine the ages for different regions of the Moon and other planetary surfaces.

Preliminary results from the new experimental studies performed at the host institution are already providing the basis for a more refined model of the Moon's early evolution and better constraints on when the Moon formed. These results are currently in preparation for publication, and a further 2-3 first author publications for the researcher are expected in addition to those already published.

The researcher has also discussed their work for an article in the EU Research and Innovation magazine ""Horizon"", a popular science podcast (""The Cosmic Cast""), and for a popular science book being written by Dr Robin George Andrews."
Cartoon illustrating the early magmatic evolution of the Moon in terms of Pb isotope compositions
Evolution of U/Pb ratios in the early Moon using old (top) & new (bottom) distribution coefficients
Scanning Electron Microscope image of an experimental run product containing ilmenite and pyroxene