This post was contributed by Dr Jennifer Harris, postdoctoral researcher in Birkbeck’s Department of Earth and Planetary Sciences. Dr Harris attended two Birkbeck Science Week 2016 events on Tuesday 12 April: Analysing the Moon (led by Dr Louise Alexander); and Looking Inside (led by Natasha Almeida)
What small fragments of rocks can tell us about the moon, the formation of the Solar System and even the early Milky Way was the subject of the second half of Birkbeck Science Week 2016’s Planetary Science evening on Tuesday 12th April.
Dr Louise Alexander, a postdoctoral researcher and Birkbeck student alumna based in the UCL/Birkbeck Centre for Planetary Sciences, and Natasha Almeida, a Birkbeck PhD student and Meteorite Curation Assistant at the Natural History Museum spent an entertaining and informative hour detailing just how much could be gleaned from tiny fragments of extra-terrestrial rocks, and how exactly they go about doing this in their own research.
Apollo Moon samples
Dr Louise Alexander
The first half of the session was dedicated to the Moon with Louise Alexander giving us an introduction to the lunar samples brought back by the Apollo astronauts that she uses in her research.
As anyone who’s ever spent any time looking at the full moon can tell you, the moon can be divided into two rough units, one bright and one dark. Lunar samples also fall into these two categories representing the dark Mare basalts and the brighter highland rocks together with a third category of pyroclastic samples. Information from these samples can be used to provide evidence to support the Giant Impact Formation theory of the moon, tell us about the moons internal structure and help to validate surface age estimates from crater counting techniques.
The particular samples that Louise’s work has focused on are all Mare Basalts and are fragments only millimetres in size. Key instruments for extracting data from such small samples are Electron Microprobes, like the one housed by Birkbeck Department of Earth and Planetary Sciences, and Gas Mass Spectrometers.
These instruments enable scientists to peer inside tiny fragments of rock and identify the different mineral crystals that comprise it. Despite the size of each sample, by looking at a large number of them Louise and her collaborators are able to build up a picture of the petrological variety that exists within the Apollo 12 site.
It’s now been over 40 years since the last samples were brought back from the moon and so it’s in the interests of those scientists lucky enough to be in possession of any of them to squeeze as much data out of them as possible. Having used them to gain an understanding of the history of the moon Louise and her colleagues are now investigating the possibility that these samples could have recorded evidence of high energy galactic events over the past few billions of years as the moon has moved through the Milky Way.
This research is still in its infancy and Dr Alexander was keen to point out that the best samples for doing this would be ones from several metres beneath the lunar surface. Sadly for this research no such samples have ever been collected, but if we were to send people back to the moon they could be!
Mapping inside meteorites
Natasha Almeida
An important consideration of the analysis that was described in the first half of the session was that many of the techniques resulted in the destruction of the sample. However not all analysis has to be destructive as we would find out from Natasha Almeida. As a curator Natasha has a professional bias towards preserving her unique and precious samples, whilst as a researcher, still wanting to exploit them as much as possible.
The Natural History Museum in London is home to the oldest collection of meteorites in the world and makes crucial loans of their 4870 samples to researchers across the globe. These meteorites are fragments of the surfaces of Mars and the Moon, and surfaces and interiors of numerous asteroids, some of which have been identified and some of which have not. In order to analyse these rare rocks Natasha uses equipment most of us will have some experience of, an X-Ray scanner, more specifically a micro-CT scanner. Just like a medical CT the NHM’s micro-CT makes use of X-rays to scan through the rock and build up a 3D picture of its interior.
There are some clear differences however; primarily the strength of the beam and the duration of the scan. Rock is more impervious to X-Rays than flesh and bone requiring a much stronger beam and a longer scan time. Each scan results in a 3D image with a resolution of down to 5mm/voxel (a voxel is a 3D pixel) and around 20 – 30Gb of data.
With these images Natasha has extracted a variety of information from numerous meteorites including spotting internal structures and features that would otherwise only be found by cutting into the sample, tracing cracks to establish the possibility of internal contamination by the atmosphere of the Earth and mapping out internal fractures and pores. This final result is especially key for meteorites as the historical methods for working out the porosity of a rock sample involve dunking it in a bucket of water. This method is a purely quantitative one that tells you how much space is in the rock but not how it is distributed unlike micro-CT.
In addition submerging your sample in a tank of water definitely counts as a high contamination risk, something meteoriticists and curators try and avoid like the plague! Unlike the electron microprobe analysis discussed in the first half of this session micro-CT for meteorite analysis is a technique that is still in its infancy but it certainly holds a lot of promise, especially if we have to wait another 40 years for people to bring us back more samples from another planetary body.
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