TEM Analysis on Wild2 cometary dust particles and impact tracks in aerogel: searching for relict structures of hydrous mineral phases

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The Stardust mission is the first mission that brought back samples from a comet and from an interstellar particle stream (ISP). Investigation on several cometary impact tracks using different techniques (Zolensky et al.2006, Brownlee et al., 2006, Flynn et al., 2006) have shown that contrary to all expectations most of the impacted mineral grains are high temperature mineral phases. Hydrous mineral phases are rare until now, only little evidence has been found, although IR data on comet Halley and Tempel 1 demonstrated the existence of hydrous phases. The lack of identified phyllosilicates in the Stardust samples may reflect diversity amongst comets or, if they were present on Wild 2 (Rotundi et al. 2008, Berger et al. 2011), that they may not have survived the capture process (Foster et al., 2008; Wozniakiewicz et al., 2010) or they may still be awaiting discovery in the Stardust collection. In either case it is clear that comets preserve evidence of aqueous processes in the early Solar System. With this proposal we would like to continue the search for aqueous mineral phases and its remnants. Therefore we propose to investigate complete impact tracks using transmission electron microscopy (TEM). For the first time new technical developments (ArIS; Stojic and Brenker, 2010) enable a TEM study of complete impact tracks. By investigating the impact path, we hope to find new information on particle chemistry and structure. Special focus will be on bulbous-shaped impact tracks. These tracks reveal the highest potential for finding hydrous phases (e.g. Maurette & Kurat, 2006). In addition we will extend our work to experimental shots of phyllosilicates into aerogel which will be performed in the framework of a cooperated project.