FIB‐TEM analysis of cometary material in 10 Stardust foil craters

FIB‐TEM analysis of cometary material in 10 Stardust foil craters

Aluminum foils from the Stardust cometary dust collector contain impact craters formed during the spacecraft's encounter with comet 81P/Wild 2 and retain residues that are among the few unambiguously cometary samples available for laboratory study. Our study investigates four micron‐scale (1.8–...

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Bibliographic Details
Published in:Meteoritics & planetary science Vol. 55; no. 6; pp. 1349 - 1370
Main Authors: Haas, Brendan A., Floss, Christine, Stroud, Rhonda M., Ogliore, Ryan C.
Format: Journal Article
Language:English
Published: Hoboken Wiley Subscription Services, Inc 01-06-2020
Subjects:
Abundance
Aerogels
Aluminum
Cometary dust
Comets
Condensates
Craters
Dust collectors
Electron microscopy
Impactors
Ion beams
Iron sulfides
Metal foils
Microscopy
Refractory materials
Residues
Silicon
Spacecraft
Temperature
Transmission electron microscopy
Wild 2 comet
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Summary:Aluminum foils from the Stardust cometary dust collector contain impact craters formed during the spacecraft's encounter with comet 81P/Wild 2 and retain residues that are among the few unambiguously cometary samples available for laboratory study. Our study investigates four micron‐scale (1.8–5.2 μm) and six submicron (220–380 nm) diameter craters to better characterize the fine (<1 μm) component of comet Wild 2. We perform initial crater identification with scanning electron microscopy, prepare the samples for further analysis with a focused ion beam, and analyze the cross sections of the impact craters with transmission electron microscopy (TEM). All of the craters are dominated by combinations of silicate and iron sulfide residues. Two micron‐scale craters had subregions that are consistent with spinel and taenite impactors, indicating that the micron‐scale craters have a refractory component. Four submicron craters contained amorphous residue layers composed of silicate and sulfide impactors. The lack of refractory materials in the submicron craters suggests that refractory material abundances may differentiate Wild 2 dust on the scale of several hundred nanometers from larger particles on the scale of a micron. The submicron craters are enriched in moderately volatile elements (S, Zn) when normalized to Si and CI chondrite abundances, suggesting that, if these craters are representative of the Wild 2 fine component, the Wild 2 fines were not formed by high‐temperature condensation. This distinguishes the comet's fine component from the large terminal particles in Stardust aerogel tracks which mostly formed in high‐temperature events.
ISSN:1086-9379
1945-5100
DOI:10.1111/maps.13438