Abstract's Details

Stardust: X-ray Microprobe Applied to Comet Dust
Abstract ID	W:MICRO-09
Presenter	Hope Ishii
Presentation Type	Microfocusing Workshop
Full Author List	H. A. Ishii (1), S. Brennan (2), J. P. Bradley (1), K. Luening (2), K. Ignatyev (3), P. Pianetta (2)
Affiliations	(1) IGPP, Lawrence Livermore National Laboratory (2) SSRL, Stanford Linear Accelerator Center (3) APS, Argonne National Laboratory
Category	Environmental Science
Abstract	X-ray microprobes are an increasingly valuable tool in astromaterials research because the most primitive extraterrestrial materials available for study on Earth are microscopic dust grains requiring nanometer-to-micron spatial resolution for meaningful analysis¹. The return in early 2006 of the NASA Stardust sample return capsule with dust from Comet 81P/Wild 2² provides a new reservoir of ancient, tiny samples. Because comets formed in the outer edges of the presolar nebula, they are expected to be cryogenic reservoirs for materials largely unchanged since the beginning of our solar system. Comet Wild 2, a recent arrival in the inner solar system, offered a pristine comet dust sample. Early studies show high temperature minerals suggesting long-distance material transport³ in the young solar system. As collaborators in the Preliminary Examination, we studied some of the first samples of known comet dust embedded in aerogel in a scanning x-ray fluorescence microprobe end station at the Stanford Synchrotron Radiation Laboratory. The adjustable spot size and sensitivity allow elemental maps and spectroscopy over the K edges of Si-Br. In addition to contributing to calculations of bulk element abundances in the comet dust⁴, element spatial distributions provide details of disaggregation and particle locations for study by other techniques like transmission electron microscopy and nano-secondary ion mass spectrometry. Challenges include studying small samples with small spot size as well as analytical separation of cometary debris from aerogel background for which we have developed a dual threshold approach. Composition and map results reveal particle diversity, an unexpected contaminant and volatile redistribution.
Footnotes	¹ Bradley, J.P. in Treatise on Geochemistry (eds. Davis, A.M., Holland, H.D. and Turekian, K.K.) vol. 1, 689-711 (Elsevier, Amsterdam, 2004). ² Brownlee, D.E. et al., Science 304, 1764-1769 (2004). ³ Brownlee, D.E. et al., Science 314, 1711-1716 (2006). ⁴ Flynn, G.J. et al., Science 314, 1731-1735 (2006).
Funding Acknowledgement	Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. This work was performed in part under the auspices of the U.S. Department of Energy, National Nuclear Security Administration by the University of California, Lawrence Livermore National Laboratory, contract No. W-7405-Eng-48. This work was partially supported by NASA Grants NNH06AD67I and SRL03-0010-0010.