New Group Paper: Meteorites from the lunar highlands

The Apollo missions visited 6 geologically complex sites of interest on the lunar surface during the 1969-1972 period and brought back around 382 kg of samples back to Earth for analysis. This amount of material has provided an idea of how the Moon formed and evolved through time, and it continues to reveal secrets about the Moon’s history.

However, they originated from a comparatively small region of the lunar surface – just 18% of the total surface of the Moon! And since Man made its first giant leap, scientists have discovered that all of the Apollo missions landed in a single ‘terrane’ or large lithological province i.e. the Procellarum KREEP terrane. The acronym KREEP stands for ‘Potassium (K), Rare Earth Elements (REE) and Phosphorus (P)’ where rare earth elements are the leftover material from the cooling of a global magma ocean (from which the lunar crust and mantle formed). As such, the Apollo samples are not entirely representative of the diversity of lithologies at the lunar surface.

The Apollo landing sites on the nearside of the Moon. Image courtesy of NASA.

Lunar meteorites have been found to originate from random locations across the Moon’s surface and therefore represent a greater range of lunar lithologies. It is important to study these meteorites in order to discover more about the regions of the Moon not explored by astronauts.

A new paper highlighting a study of three lunar meteorites that has taken place here in Manchester has recently been published in Meteoritics and Planetary Science. It was written by myself and five colleagues; two of which are Dr Katherine Joy and Dr John Pernet-Fisher of the Isotope Geochemistry and Cosmochemistry group. The other co-authors are based in other research groups in Manchester and in Münster, Germany as part of a European wide collaboration.

The study focussed on analysing the three lunar meteorites (Miller Range 090034, 090070, and 090075) collected in Antarctica by the US Antarctic Search for Meteorites programme (ANSMET) in 2009. They are the same samples that Abigail Calzada-Diaz from Birkbeck College discussed in a previous Earth and Solar System blog post.

In our new study we used Fourier-Transform Infrared Spectrometer (FTIR) and an Electron Probe Micro-Analyser (EPMA) laboratory instruments. The spectrometer has an attached high-resolution mapping unit and provided mid-infrared spectra of specific minerals within the meteorite samples (as small as 10 microns!). This provided information on the internal structure of the minerals and glass phases present within the samples. The EMPA instrument provided precise chemical information of the minerals and glass present, allowing us to understand the chemical composition of the different mineral and glass phases present.

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Of specific interest was the identification of shocked minerals present in the meteorites. As the Moon has no atmosphere, asteroids and comets are continually bombarding the lunar surface, altering the minerals and rocks present by melting or shocking them. The meteorites are made of minerals that have been shocked by different amounts, each of which could be attributed to different times in their histories. This allowed us to explore the impact history of these samples and of part of the lunar surface. Also, it has helped develop new ways of analysing planetary samples by using high-resolution FTIR  lab techniques.

An electron microscope was used here at the University of Manchester to obtain high-resolution back-scattered electron images of the three lunar meteorites. Brighter regions have higher amounts of heavier elements so the melt veins are easy to see as they contain more iron! Image from Martin et al. 2017

It is hoped that this method will be expanded upon and used more frequently by the planetary science community in order to discover more about the shocked nature of their samples (whether it be meteorites, lunar samples or even samples from terrestrial impact craters such as those found in and around the Ries crater). Studies using this FTIR technique are being developed further here in Manchester by analysing powders and Apollo regolith samples. Watch this space – there is more to follow!

 

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The full citation for the new paper is below and it can be accessed here

Martin D.J. P., Pernet-Fisher J.F., Joy K. H., Wogelius R. A., Morlok A., and Hiesinger H. (2017) Investigating the shock histories of lunar meteorites Miller Range 090034, 090070, and 090075 using petrography, geochemistry, and micro-FTIR spectroscopy. Meteoritics & Planetary Science doi: 10.1111/maps.12860.