Correlated Microanalysis of Cometary Organic Grains Returned by Stardust

摘要

Preliminary examination (PE) of samples returned from Comet 81P/Wild 2 by the NASA Stardust mission revealed a wide variety of carbonaceous samples (e.g. 1). Carbonaceous matter is present as inclusions, rinds, and films in polyminerallic terminal particles (2-4), as carbon-rich particles along track walls (2, 5, 6), and as organic matter in aerogel around tracks (7, 8). The organic chemistry of these samples ranges from purely aliphatic hydrocarbons to highly-aromatic material, often modified by various organic functional groups (2, 4, 5, 9-11). Difficulty arises when interpreting the genesis of these carbonaceous samples, since contaminants could be introduced from the spacecraft (12), aerogel (1, 8), or during sample preparation. In addition, hypervelocity capture into aerogel may have heated cometary material in excess of 1000 C, which could have significantly altered the structure and chemistry of carbonaceous matter. Fortunately, much of this contamination or alteration can be identified through correlated microanalysis with transmission electron microscopy (TEM), scanning-transmission X-ray microscopy (STXM), and nanoscale secondary ion mass spectroscopy (SIMS).