A couple of months ago I wrote about NASA’s Genesis mission, which collected solar wind to return to Earth for chemical analysis.
Unfortunately the return to Earth didn’t go quite to plan: the parachutes on the sample return capsule failed to open and the capsule hit the ground at 193 miles per hour. The impact severely damaged the capsule and the collector targets inside. The capsule was taken from the landing zone in the Utah desert to the Johnson Space Centre in Houston, where a team of scientists began the painstaking task of trying to see whether any of the collector targets could be salvaged…
The collector targets had originally been pristine arrays of hexagons. Now they look a little different – the impact of the landing smashed them into thousands of tiny pieces. Putting the pieces back together is a very difficult jigsaw puzzle!
Fortunately most of the different materials used in the collector targets can be distinguished by their appearance. And for those materials that have similar appearances, a technique called Fourier Transform Infrared Spectroscopy (FTIR) can be used to distinguish them.
What’s more, someone (I’m tempted to say a genius!) had the foresight to insist that the hexagons used in each different collector array were made to different, specific thicknesses.
Combining the differences in appearance and thickness, and a lot of hard work, has enabled the curators to figure out which collector array thousands of pieces (ranging from a few mm2 to over 300mm2) originated from, and what material they are made from. Each sample is assigned a unique classification number, and as of January 2011 close to 4000 samples had been catalogued. But this only represents less than 20% of the total area of the collectors, there’s still a long way to go…
The next step is to accurately measure the length, width and area of irregularly shaped pieces. Many pieces are scratched or have chips missing from the edges. But it is important to know the surface area in order to calculate the concentration (per unit area) of the implanted solar wind for the different elements.
The crash landing exposed the samples to the desert sand. After cataloguing, the samples then have to be cleaned to remove sand and dust from the surface. But the solar wind is implanted only a fraction of a millimetre below the surface, so the curation team had to develop a technique which would remove sand and dust without scratching the surface – even the smallest scratch would remove the very top atomic layers of a sample, exactly where the solar wind is implanted. The curation team have developed a technique which involves rotating the samples 3000 times per minute in ultra pure water – this is known as UPW/Megasonic cleaning. This is followed by further cleaning with ultra violet light and ozone to remove organic films.
Once the samples have been identified, catalogued and cleaned, they are ready to be sent out to researchers, members of the Genesis Science Team, for analysis. Different research groups, from all around the world, are analysing samples. Each group is responsible for one particular type of analysis, based on their particular expertise.