Synchrotron X-rays in situ analysis of extraterrestrial grains trapped in aerogel

Abstract

In January 2006, the NASA Stardust mission will return, trapped in aerogel, the first samples of cometary and contemporary interstellar dust. Their analyses will require high spatial resolution techniques. An example is Synchrotron X-ray analysis, which could be useful for in situ identification of the captured grains. In the case of aerogel, it is possible to optically scan the samples and locate the trapped grains, which can then be extracted in pieces of aerogel, called “keystones”, a few hundreds of microns large and self-supported on microforklifts that contain one incident grain and its penetration track. The non-destructive identification of the material distributed inside a keystone can be completed using Synchrotron X-ray microbeams either in the fluorescence or the absorption mode. In order to develop an analytical protocol, we analysed a keystone containing a dust grain originating from the chondritic swarm identified in the Orbital Debris Collection Experiment (ODCE) that was deployed for 18 months outside the Russian space station MIR. The results we present concern μ-fluorescence mappings and XANES at the Fe K-edge measurements. They indicate a very strong tendency of the incident particle to break up into many fragments during the slowing in the aerogel. Furthermore, a structural evolution of the grain is also possible, during the slowing down in the aerogel. These non-destructive techniques might be among the only ones to be used for analysing the interstellar grains trapped in the Stardust aerogel and for those cometary grains that might have lost most of their material along the penetration track.