In situ identification of a CAI candidate in 81P/Wild 2 cometary dust by confocal high resolution synchrotron X-ray fluorescence

Geosciences Institute/Mineralogy, Goethe University Frankfurt, Altenhoeferallee 1, D-60438 Frankfurt, Germany
Geochimica et Cosmochimica Acta (Impact Factor: 4.33). 09/2009; 73(18):5483-5492. DOI: 10.1016/j.gca.2009.06.008


We detected additional CAI-like material in STARDUST mission samples of comet 81P/Wild 2. Two highly refractory cometary dust fragments were identified in the impact track 110 [C2012, 0, 110, 0, 0] by applying high resolution synchrotron induced confocal and conventional XRF analysis (HR SR-XRF). The use of a polycapillary lens in front of the detector for confocal spectroscopy dramatically improves the fidelity of particle measurements by removing contribution from the surrounding aerogel. The high spatial resolution (300 × 300 nm2; 300 × 1000 nm2) obtained allowed the detailed non-destructive in situ (trapped in aerogel) study of impacted grains at the sub-μm level.For the two largest particles of the track, the terminal particle and a second particle along the impact track, Ca concentration is up to 30 times higher than CI and Ti is enriched by a factor of 2 compared to CI. High resolution (HR) SR-XRF mapping also reveals that the highest concentrations of Ca, Ti, Fe (and Ni) measured within each grain belongs to different areas of the respective maps which indicate that the particles are composed of several chemically diverse mineral phases. This is in agreement with the finding of a complex phase assemblage of highly refractory minerals in the first ever detected Stardust mission CAI grain “Inti” of Track 25.Principle component analysis (PCA) is a powerful tool for extracting the dominant mineral components and was applied to the two grains indicating that regions in the terminal particle and the second particle are consistent with anorthite or grossite and gehlenite, monticellite or Dmitryivanovite (CaAl2O4), respectively.Our new findings demonstrate that the HR SR-XRF with confocal geometry and PCA analysis is capable of identifying CAI-like fragments without the need to extract particles from the aerogel matrix which is a time-consuming, complex and destructive process.Furthermore, the detection of new CAI-like fragments in the coma dust of comet 81P/Wild 2 strengthens the observation that strong mixing effects and, therefore, mass transport before or during comet formation must have occurred at least up to the region where Kuiper Belt comets formed (∼30 AU).

12 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Compared to other microscopic analytical tools X-ray microscopy techniques have the advantage that the large penetration depth of X-rays in matter allows one to investigate the interior of an object without destructive sample preparation. In combination with X-ray fluorescence tomography, analytical information from inside of a specimen can be obtained. Different X-ray analytical techniques can be used to produce contrast, X-ray absorption, fluorescence, and diffraction, to yield chemical, elemental, and structural information about the sample. Scanning microscopy on the basis of various lens systems in synchrotron radiation sources provides a routine spatial resolution of now about 100 nanometer but in the foreseeable future a 10–20 nanometer spatial resolution can be expected. X-ray absorption spectrometry can also provide chemical (speciation) information on the sample. All this makes X-ray microscopy attractive to many fields of science. In this paper the techniques are briefly reviewed and a number of applications in the earth, planetary and cosmos sciences are illustrated with state-of-the art examples, while applications in the environmental sciences and biology are also briefly discussed.
    The European Physical Journal Conferences 12/2010; 9. DOI:10.1051/epjconf/201009013
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Micro X-ray fluorescence analysis (μ-XRF) is one of the newest branches of XRF, which has developed very rapidly since 1990. In this review, we first discuss a number of papers that describe advances in instrumentation and (calibration) methods that can contribute towards more reliable quantitative analysis using μ-XRF. This first part also includes recent papers that aim to characterize the heterogeneity of standards useful for calibrating μ-XRF set-ups.We then present a short overview of recently published papers in which the (semi-)quantitative nature of μ-XRF is exploited, including studies in which μ-XRF is compared to other microanalytical methods providing compositional information or is used in combination with other methods in order to characterize materials more completely.
    TrAC Trends in Analytical Chemistry 06/2010; 29(6-29):464-478. DOI:10.1016/j.trac.2010.03.003 · 6.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this review we highlight the performance of confocal micro X-ray fluorescence (CMXRF) for application in environmental science, citing contributions from recent studies (2008-2010). In CMXRF the use of focusing and collecting optics enables discrimination of the origin of fluorescence photons in three dimensions. It thereby enables simple and direct three dimensional imaging, and also the removal of unwanted signal contribution either from the depth of the sample or from its surface. By limiting the area of origin of fluorescence signal CMXRF can simplify quantitative approaches.
    Analytical and Bioanalytical Chemistry 04/2011; 400(6):1743-50. DOI:10.1007/s00216-011-4873-y · 3.44 Impact Factor
Show more