Newly published paper led by group member Katherine Joy discusses the discovery of an oxidised iron mineral found in a sample returned from the Moon by Apollo 16 astronauts. Working with an international team of collaborators in the US and Japan, Joy et al. investigated an ancient lunar soil sample (known as a regolith breccia), which is a complicated mixture of mineral and rock fragments sourced from many different origins consolidated together in a single rock. Within sample 60016 (see links below and the photo of the sample in the NASA curation lab) the team located a tiny piece (only 70 × 50 microns in size!) of a rock that hosts the mineral magnetite. They characterised the phase using a range of analytical techniques including a scanning electron microscope, an electron microprobe and synchrotron X-ray Absorption Near Edge Spectroscopy (XANES) and X-ray Diffraction (XRD) analysis to prove that the mineral discovered was in fact magnetite.
The Moon is highly reduced in nature (i.e., minerals formed under low oxygen conditions) compared with the Earth and Mars: on the Moon Fe-minerals are typically found in the ferrous state (also known divalent or 2+ iron) rather than ferric (known as trivalent 3+ iron) oxidation state. Magnetite, with its trivalent iron component is formed at higher oxygen fugacity conditions than is normal for lunar sample. Therefore, although small in size, this discovery of magnetite is exciting as it provides direct evidence for oxidised conditions on the Moon in the past. What could have caused such oxidised conditions?
The paper explores different formation pathways using calculations of chemistry and temperature reactions and concludes that the magnetite was likely formed due to a low temperature (<570°C) process. Such oxidising conditions may have arisen from vapour transport at the lunar surface, although the source of these gases or even fluids is enigmatic, with theories ranging from magmatic degassing, to mobilisation of lunar volatiles by hot impact melt ejecta blankets. Understanding the nature and history of lunar volatiles is a very important lunar science goal, and this discovery adds new information to the debate about the cycling of volatile-rich gases and fluids at the lunar surface.
This research was funded by the Leverhulme Trust in the UK and by NASA NLSI and SSERVI in the US.
Full citation is: Joy K. H., Visscher C., Zolensky M. E., Mikouchi T., Hagiya K., Ohsumi K., and Kring D. A. (2015). Identification of Magnetite in Lunar Regolith Breccia 60016: evidence for oxidised conditions at the lunar surface. Meteoritics and Planetary Science. DOI: 10.1111/maps.12462
Publisher website: http://onlinelibrary.wiley.com/doi/10.1111/maps.12462/abstract
University of Manchester holdings: https://www.escholar.manchester.ac.uk/uk-ac-man-scw:265517
Find out more about sample 60016 itself at http://www.lpi.usra.edu/lunar/samples/atlas/detail/?mission=Apollo%2016&sample=60016
Explore the Apollo 16 landing site in detail where sample 60016 was collected from’ station 0′ (the Lunar Module landing station) at the amazing LRO mission Narrow Angle Camera mission page at http://www.lroc.asu.edu/featured_sites/view_site/11 (click on and off at the bottom to see the astronaut’s traverses)
You can find out more about the usefulness of the Apollo 16 regolith breccias from http://www.sciencedirect.com/science/article/pii/S0016703711005394 and also in the regolith chapter of the Lunar Sourcebook available at http://www.lpi.usra.edu/publications/books/lunar_sourcebook/