Computer Science
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....4087g&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #4087
Computer Science
Scientific paper
The capture of intact cosmic dust grains, wherein both volatile chemical components and the mineral stoichiometry have survived, has proven difficult to achieve. However, development of low-density silica aerogel capture cells has been stimulated by the preparation for the NASA Stardust mission. To see what material this mission has collected, the research community must wait until 2006 for the return of the spacecraft, currently en route to Comet Wild 2. This interim period between launch and sample return should be used to assess the capabilities and difficulties of aerogel use, with low Earth orbit (LEO) flight opportunities and the development of extraction and analysis protocols in the laboratory. The ground-based studies are particularly important as LEO opportunities are limited, the last space-flown aerogel capture cell was on the now de-orbited MIR space station. Despite the paucity of orbital data, it is possible to simulate the expected cometary encounter velocities of the Stardust collectors using light-gas-gun and Van de Graaff particle accelerators. We have carried out a series of hypervelocity impact experiments using aerogel targets, with a variety of aerogel densities and compositions. A range of projectiles were used, from simple single homogeneous minerals (e.g. olivine) to complex crushed heterogeneous meteorite powders. The impacted targets were subjected to preliminary characterisation using optical and Raman microscopy, to assess location, composition and mineralogy of the captured grains. We have previously reported successful extraction of individual grains, and tracks containing fragments, by use of a UV laser system (COSPAR, 2002). During the impact between the projectile and the aerogel target, a thin layer of denatured aerogel is deposited on the grain, our preliminary experiments have shown that this aerogel coating can be removed from the grain surface by use of in-situ focused ion beam (FIB) techniques. We are now developing the application of FIB microscopy to further assist particle extraction. It is possible to ion-mill precise volumes of aerogel at controlled rates, whilst acquiring both secondary electron and ion images to monitor the milling progress. We believe that it is now timely to refine these techniques, particularly those relating to extraction, so they can be applied confidently and routinely to this unique and yet challenging capture medium.
Bradley John P.
Burchell Mark J.
Chater Richard J.
Graham Giles A.
Kearsley Anton T.
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