HR: 1340h
AN: MR13C-1395    [Abstracts]
TI: What was the cooling rate of cometary dust particles when they were collected by the Stardust spacecraft ?
AU: * Roskosz, M
EM: mathieu.roskosz@univ-lille1.fr
AF: Laboratoire de Structure et Propriétés de l'Etat Solide, Université des Sciences et Techniques de Lille Bat C6, Villeneuve d'Ascq, 59655, France
AU: Watson, H C
EM: watson40@llnl.gov
AF: Lawrence Livermore National Laboratory, Earth and environment, 7000 east Avenue L- 206, Livermore, CA 94550, United States
AU: Leroux, H
EM: hugues.leroux@univ-lille1.fr
AF: Laboratoire de Structure et Propriétés de l'Etat Solide, Université des Sciences et Techniques de Lille Bat C6, Villeneuve d'Ascq, 59655, France
AB: Cometary dust particles are considered as relicts of pristine materials that accreted to form primitive meteorites and eventually planets. Compared to other small primitive objects of the solar system, cometary grains are poorly known. In this respect, the first sample return of cometary materials, the Stardust mission, raised considerable expectations from astrophysicists, geologists and cosmochemists. Indeed, these dusts are the only undisputable comet samples available so far. The mission was a plain success but still had to face inherent problems related to the collect of samples itself. The grains were captured from the 81P/Wild 2 comet tail at a relative velocity of 6.1 km/s in a low density silica aerogel medium. During this hypervelocity impact, flash heating of dusts could not be avoided. This thermal event may hinder detailed understanding of dust mineralogy and geochemistry because the parameters of this flash heating are not well constrained. Models and experiments tend to indicate a high peak temperature, strong thermal gradients and a very fast quench (within a few microseconds). In this study we estimate the parameters of the flash heating based on the interdiffusion of MgO and SiO₂ between molten MgO-rich cometary dust particles and the embedding molten aerogel. The presence of a miscibility gap in the MgO-SiO₂ binary system precludes full mixing of the Mg-rich melt and the surrounding melted aerogel. The persistence of the two coexisting molten domains, the extend of the MgO contamination of the silica matrix and the shape of the inter-diffusion profile are then used to shed light on the thermal history of cometary dusts particles collected by the spacecraft. Comparison between the models and experimental work will be detailed, together with potential implications on the thermal alteration (intensity of heating and kinetics) of cometary grains during their capture.
DE: 3652 Pressure-temperature-time paths
DE: 5120 Plasticity, diffusion, and creep
DE: 5134 Thermal properties
DE: 6022 Impact phenomena (5420, 8136)
DE: 6023 Comets: dust tails and trails (6210)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting