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Dust from comet Wild 2: Interpreting particle size,
shape, structure and composition from impact features on the Stardust
aluminum foils.
Kearsley A. T., Borg J., Graham G. A., Burchell M. J., Cole M.
J., Leroux H., Bridges J. C., Hörz F., Wozniakiewicz P. J., Bland
P. A., Bradley J. P., Dai Z. R., Teslich N., See T., Hoppe P., Heck P.
R., Huth J., Stadermann F. J., Floss C., Marhas K., Stephan T., and
Leitner J. (2008)
Meteorit. Planet. Sci. 43(1/2), 41-73.
ABSTRACT
Aluminum foils of the Stardust cometary dust collector are
peppered with impact features of a wide range of sizes and shapes. By
comparison to laboratory shots of known particle dimensions and
density, using the same velocity and incidence geometry as the Stardust
Wild 2 encounter, we can derive size and mass of the cometary dust
grains. Using scanning electron microscopy of foil samples (both flown
on the mission and impacted in the laboratory) we have recognised a
range of impact feature shapes, from which we interpret particle
density and internal structure. We have documented composition of
crater residues, including stoichiometric material in 3 of 7 larger
craters, by energy dispersive X-ray microanalysis. Wild 2 dust grains
include coarse (>10 µm) mafic silicate grains, some dominated
by a single mineral species of density around 3 - 4 g cm-3
(such as olivine). Other grains were porous, low density aggregates
from a few nanometers to 100 µm, with overall density that may be
lower than 1 gcm-3, containing mixtures of silicates and
sulfides and possibly both alkali-rich and mafic glass. The mineral
assemblage is very similar to the most common species reported from
aerogel tracks. In one large aggregate crater the combined, diverse
residue composition is similar to CI chondrites. The foils are a unique
collecting substrate, revealing that the most abundant Wild 2 dust
grains were of sub-micrometer size, and of complex internal structure.
Impact residues in Stardust foil craters will be a valuable resource
for future analyses of cometary dust.
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