Synchrotron x-ray fluorescence analysis of the first track

Last week, Frank Brenker and his colleagues Bart Vekemans, Laszlo Vincze, and Manfred Burghammer analyzed the first track to be extracted from the Stardust Interstellar Collector. We suspected that this is a particle that was ejected from an impact of a high-velocity particle (either an interplanetary dust particle or an interstellar dust particle) on the port (left-side) aft solar panel. We thought that this would be the case for two reasons. We mainly based this expectation on the trajectory — it appears to be pointing back to the aft solar panel — but also on the track shape — it does not show the shock-induced flaring that one usually sees with hypervelocity impacts. Dr. Brenker and colleagues used a highly focussed x-ray beam at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. ESRF is essentially an x-ray microscope the size of a shopping mall. The incredibly tight focus of this beam (about a tenth of a micron!) is ideal for the analysis of these very tiny samples. The use of x-ray fluorescence is also ideal for the analysis of these particles, because you can analyze particles while they are still in the aerogel keystones — there is no need to extract them.

Dr. Brenker found that the captured particle was very rich in the elements cerium and zinc. This is consistent with the glass covering over the solar panels. But there was also a surprise: there was a substantial amount of iron and nickel. These are not expected to be present in the solar panel glass, but are very commonly found in extraterrestrial materials. (Iron-56 is the most tightly bound nucleus in Nature, is made in prodigious quantities in supernovae, and is very commonly found in extraterrestrial materials.) So it appears that not only do we have materials from the spacecraft, which we expected, we also have our first sample of extraterrestrial material capture in the interstellar collector, which we did not! The next steps are to do more detailed, non-destructive analysis on this track, and the other two tracks that have been extracted. Eventually, these tracks will be made available to the scientific community to request to for doing destructive analyses. For example, these particles couldbe extracted from their keystones, sliced into extremely thin slices using a diamond knife, and analyzed by Transmission Electron Microscopy, or they could be analyzed for their isotopic abundances in very sensitive mass spectrometers, like the Cameca nanoSIMS.