Thermal alteration of hydrated minerals during hypervelocity capture to silica aerogel at the flyby speed of Stardust

Noguchi, Takaaki and Nakamura, Tomoki and Okudaira, Kyoko and Yano, Hakime and Sugita, Seiji and Burchell, Mark J. (2007) Thermal alteration of hydrated minerals during hypervelocity capture to silica aerogel at the flyby speed of Stardust. Meteoritics & Planetary Science, 42 (3). pp. 357-372. ISSN 1086-9379. (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Outside the Earth's atmosphere, silica aerogel is one of the best materials to capture fine-grained extraterrestrial particles in impacts at hypervelocities. Because silica aerogel is a superior insulator, captured grains are inevitably influenced by frictional heat. Therefore, we performed laboratory simulations of hypervelocity capture by using light-gas guns to impact into aerogels fine-grained powders of serpentine, cronstedtite, and Murchison CM2 meteorite. The samples were shot at > 6 km s(-1) similar to the flyby speed at comet P/Wild-2 in the Stardust mission. We investigated mineralogical changes of each captured particle by using synchrotron radiation X-ray diffraction (SR-XRD), transmission electron microscope (TEM), and field emission scanning electron microscope (FE-SEM). SR-XRD of each grain showed that the majority of the bulk grains keep their original mineralogy. In particular, SR-XRD, and TEM investigations clearly exemplified the presence of tochilinite whose decomposition temperature is about 300 degrees C in the interior of the captured Murchison powder. However, TEM study of these grains also revealed that all the samples experienced melting and vesiculation on the surface. The cronstedtite and the Murchison meteorite powder show remarkable fracturing, disaggregation, melting, and vesiculation. Steep thermal gradients, about 2500 degrees C/mu m were estimated near the surface of the grains (< 2 mu m thick) by TEM observation. Our data suggests that the interior of > 4 mu m across residual grains containing abundant materials that inhibit temperature rise would have not experienced > 300 degrees C at the center.

Item Type: Article
Subjects: Q Science > QE Geology
Q Science > QD Chemistry
Q Science > QC Physics
Divisions: Faculties > Science Technology and Medical Studies > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Suzanne Duffy
Date Deposited: 21 Apr 2008 08:24
Last Modified: 30 Apr 2014 11:09
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