Three‐dimensional structures and elemental distributions of Stardust impact tracks using synchrotron microtomography and X‐ray fluorescence analysis

Abstract

available online at http://meteoritics.org Abstract-Three-dimensional structures and elemental abundances of four impact tracks in silica aerogel keystones of Stardust samples from comet 81P/Wild 2 (bulbous track 67 and carrot-type tracks 46, 47, and 68) were examined non-destructively by synchrotron radiation-based microtomography and X-ray fluorescence analysis. Track features, such as lengths, volumes and width as a function of track depth, were obtained quantitatively by tomography. A bulbous portion was present near the track entrance even in carrot-type tracks. Each impact of a cometary dust particle results in the particle disaggregated into small pieces that were widely distributed on the track walls as well as at its terminal. Fe, S, Ca, Ni, and eight minor elements are concentrated in the bulbous portion of track 68 as well as in terminal grains. It was confirmed that bulbous portions and thin tracks were formed by disaggregation of very fine fragile materials and relatively coarse crystalline particles, respectively. The almost constant ratio of whole Fe mass to track volume indicates that the track volume is almost proportional to the impact kinetic energy. The size of the original impactor was estimated from the absolute Fe mass by assuming its Fe content (CI) and bulk density. Relations between the track sizes normalized by the impactor size and impact conditions are roughly consistent with those of previous hypervelocity impact experiments. Three-dimensional structures and elemental distributions of Stardust impact tracks using synchrotron microtomography and X-ray fluorescence analysis

Absorption Efficiencies of Forsterite. I. Discrete Dipole Approximation Explorations in Grain Shape and Size

“…Condensation origin for forsterite crystals is strongly supported by laboratory examination of forsterite crystals in cometary interplanetary dust particles (Bradley et al 1983;Molster et al 2003), which are described as having equant and tabular crystal habit (J. Bradley 2011, private communication), and in Stardust samples (Brownlee et al 2006;Nakamura et al 2008;Tsuchiyama et al 2009). Hence, our shape classes can be used in an effort to ascertain the formation conditions of forsterite crystals that are observed in astronomical sources.…”

“…Stardust samples of comet 81P/Wild 2 include large (∼20 μm) single mineral crystals (Brownlee et al 2006), and X-ray microprobe analysis indicates a f cryst > 0.5 (Ogliore et al 2009). These crystals are thought to be condensates (Brownlee et al 2006;Nakamura et al 2008;Tsuchiyama et al 2009). The discrepancy between ISM and solar system abundances of crystalline silicates indicates that the solar system crystals must be a product of the formation and evolution of a dusty disk with a radial thermal gradient.…”

Laboratory technology and cosmochemistry

“…Images of X-ray attenuation yield 3D density structure. This technique has been applied to determine the location and size of cometary particle fragments in Stardust aerogel tracks (77,78). X-ray tomography can also be done from XRF images and thus, provides the 3D distribution of different elements.…”

Structural Characterization of Iron Meteorites through Neutron Tomography

“…Mostly, the projections are acquired with equiangular steps over either 180˝or 360˝to cover the whole sample. In the last decade, X-ray computed tomography (X-ray CT) has been successfully applied to the study of planetary materials, such as chondrites [5][6][7][8][9][10][11][12], stardust [13,14], and tektites [15,16].…”