An international collaboration that included researchers at SSRL has used x-ray scanning microprobe fluorescence techniques at BL6-2 to characterize the elemental chemistry of samples from comet 81P/Wild-2 brought back aboard the Stardust spacecraft last January. Twenty-three aerogel samples containing cometary particles were analyzed by the 175-member Preliminary Examination Team, and five of those samples were studied at SSRL. This collaboration provided the first look at the Stardust samples after the return, and results are presented in several publications in the December 15 issue of Science.

Until 1974, comet 81P/Wild 2 orbited beyond Jupiter, but a gravitational kick from that planet altered its orbit transforming it into a short-period comet in the inner solar system. This allowed NASA's solar-powered Stardust spacecraft to intercept the comet's tail within the orbit of Mars. The fly-by was completed at a relative speed of 6.1 km/s passing through the coma of the comet. Microscopic dust grains were captured in low-density silica aerogel tiles and aluminum foils, and these samples were returned successfully to Earth in January 2006. These Stardust samples are unique among extraterrestrial materials on Earth as the first samples returned from an identified parent body originating in the Kuiper belt beyond the gas giants. Due to the very recent orbit change, dust from Comet Wild 2 provides a means of inferring conditions in the Kuiper belt, and thus, theoretically, the origins of the solar system. First order, fundamental research involves understanding the elemental and isotopic chemistry, the astronomical signatures, the organics and mineralogy of these samples.

The mean elemental composition of the Stardust Comet 81P/Wild 2 dust measured is generally consistent with the CI meteorite composition, believed to be representative of the overall composition of the solar system. A few elements, Cu, Zn and Ga, are enriched suggesting that the CI meteorites may not be entirely representative of the solar system composition for these moderately volatile elements.

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/stardust.html

G. J. Flynn, P. Bleuet, J. Borg, J. P. Bradley, F. E. Brenker, S. Brennan, J. Bridges, D. E. Brownlee, E. S. Bullock, M. Burghammer, B. C. Clark, Z. R. Dai, C. P. Daghlian, Z. Djouadi, S. Fakra, T. Ferroir, C. Floss, I. A. Franchi, Z. Gainsforth, J.-P. Gallien, P. Gillet, P. G. Grant, G. A. Graham, S. F. Green, F. Grossemy, P. R. Heck, G. F. Herzog, P. Hoppe, F. Hörz, J. Huth, K. Ignatyev, H. A. Ishii, K. Janssens, D. Joswiak, A. T. Kearsley, H. Khodja, A. Lanzirotti, J. Leitner, L. Lemelle, H. Leroux, K. Luening, G. J. MacPherson, K. K. Marhas, M. A. Marcus, G. Matrajt, T. Nakamura, K. Nakamura-Messenger, T. Nakano, M. Newville, D. A. Papanastassiou, P. Pianetta, W. Rao, C. Riekel, F. J. M. Rietmeijer, D. Rost, C. S. Schwandt, T. H. See, J. Sheffield-Parker, A. Simionovici, I. Sitnitsky, C. J. Snead, F. J. Stadermann, T. Stephan, R. M. Stroud, J. Susini, Y. Suzuki, S. R. Sutton, S. Taylor, N. Teslich, D. Troadec, P. Tsou, A. Tsuchiyama, K. Uesugi, B. Vekemans, E. P. Vicenzi, L. Vincze, A. J. Westphal, P. Wozniakiewicz, E. Zinner, M. E. Zolensky, "Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust", Science 314, 1731-1735 (2006).