Museum meteorite CT scans help prepare for space missions

29 April 2013

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A meteorite from Mars is a rare thing - even the Natural History Museum's world-class collection has only 13. Scientists are planning robotic missions to Mars to collect more Martian samples. But what is the best way to study these precious objects once they're returned to Earth?

One method is to use CT scanners, and scientists at the Museum are producing incredibly detailed images that are impressing scientists all over the world.

They are working with colleagues at the European Space Agency and the UK Space Agency to find the best way to look after and study Martian samples brought back from future missions. Investigating Mars samples will be key to finding out things such as whether there was ever life on Mars.

CT scans reveal a void, or air space, at the centre of this Tissint Martian meteorite

CT scans reveal a void, or air space, (in black) at the centre of this Tissint Martian meteorite.

'These samples will be amongst the most precious rocks on Earth,' says Museum meteorite expert Dr Caroline Smith. 'Just like with the rare and precious samples from the Museum collections we want to maximise the amount of information available whilst minimising the level of damage to the sample in obtaining that information'.

CT scans are non-destructive and reveal incredible detail that could remain locked away for a long time. For example, they have already revealed voids, or air spaces at the centre of a meteorite, shown in the video above. Smith explains, 'Most excitingly we can clearly see the voids in the black glassy phase.

’These are potentially very exciting because if they are completely sealed they may retain trapped Martian atmosphere.'

Halfway through the video, the black void is highlighted in red and shows that the air pocket connects to the outside of the meteorite, meaning that in this case, sadly, any air will probably have escaped long ago.

Traditional destructive method
CT scan of Tissint meteorite showing its external surface and the internal cracks, coloured red.

CT scan of Tissint meteorite showing its external surface and the internal cracks, coloured red.

The main problem with studying meteorites is that traditional methods are usually destructive. For example, to study meteorites with an electron microscope, small samples need to be broken off and prepared - they are embedded in resin, polished and coated in a thin layer of carbon. As well as potentially damaging the meteorite, contamination can also be introduced.

Benefits of CT scans

No preparation is needed, however, when using the Museum's micro-CT scanner.

To CT scan an object, you take X-ray slices through it. These slices can then be stacked to produce 3D reconstructions or 'virtual volumes' that allow the inside of the meteorite to be analysed.

Red coloured spaces show the void in centre and channels that would have let air escape.

Air spaces coloured red show the void in the centre and channels that would have let air escape to the outside of the meteorite.

Meteorite samples the size of a fingernail can give 2 or 3 traditional sections. 'With the CT data we are getting between 1,500 and 2,000 virtual slices. It's almost like having that number of sections,' says Smith.

'The thing we found the most surprising was the level of detail that can be detected'.

'Depending on the size of the sample we are looking at, we can see features down to about 5 microns in size [an average human hair is 100 microns in diameter].

Dr Farah Ahmed, Museum CT Facility Manager and Specialist who scanned the meteorites says, 'Micro-CT has become an incredibly powerful tool over the last 10 years. With its non-destructive nature and highly detailed imaging, CT scanning has proven to be a successful technique in a museum environment'.

Studying Museum meteorites
Museum scientist Dr Caroline Smith holds the newly arrived Tissint Martian meteorite

Museum scientist Dr Caroline Smith holds the Tissint meteorite. It is now the largest Martian meteorite in the Natural History Museum collections.

The video is a CT scan of the Museum's Tissint Martian meteorite - a very important specimen that landed on Earth in July 2011. It's less likely to be contaminated than other meteorites because it was recovered soon after it fell.

Martian meteorites are some of the most requested meteorites for study at the Museum and the Tissint is certainly one of the most popular.

With the CT scanner, Museum scientists can take a detailed look and select the most suitable samples to be sent to external researchers. Even if the sample to be analysed is destroyed, a virtual record is left behind.

Seven Museum meteorites, including Tissint, have been scanned so far as part of the space mission sample returns project. The CT scans are producing important data and have been impressing crowds at international conferences.

'Our results so far are very exciting,' concludes Smith. 'We are testing a potential technique that we could use in the future for studying Mars samples returned by space missions. And we're able to use actual Mars samples in the form of meteorites!

'This work shows that we can combine our fantastic collections with our cutting-edge technology to produce some great science.'

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