Carbon XANES Data from Six Aerogel Picokeystones Cut From the Top and Bottom Sides of the Stardust

Introduction: Great care and a large effort was made to minimize the amount of organic matter contained within the flight aerogel used to collect Comet 81P/Wild 2 samples [1]. Even so, by the very nature of the production process and silica aerogel’s affinity for volatile organics keeping silica aerogel free from organics is a monumental task. Silica aerogel from three production batches was flown on the Stardust sample return mission. All 3 types had layered densities varying from 5mg/ml to 50 mg/ml where the densest aerogel was farthest away from the collection area. A 2 step gelation process was used to make the flight aerogel and organics used in this process were tetraethylorthosilicate, ethanol and acetonitrile. Both ammonium hydroxide and nitric acid were also used in the aerogel production process. The flight aerogel was baked at JPL at 300 ° C for 72 hours, most of the baking was done at atmosphere but twice a day the oven was pumped to 10 torr for 1⁄2 hour [1]. After the aerogel was baked it was stored in a nitrogen purged cabinet until flight time. One aerogel cell was located in the SRC away from any sample collection area as a witness to possible contamination from out gassing of the space craft, re-entry gasses and any other organic encounter. This aerogel was aerogel used in the interstellar collection sample tray and is the least dense of the 3 batches of aerogel flown. Organics found in the witness tile include organics containing Si-CH3 bonds, amines and PAHS [2,3]. Besides organic contamination, hot spots of calcium were reported in the flight aerogel [4]. Carbonates have been detected in comet 81P/Wild2 samples [5]. During preflight analyses, no technique was used to analyze for carbonates in aerogel. To determine if the carbonates found in 81P/Wild2 samples were from the comet, it is necessary to analyze the flight aerogel for carbonate as well as for organics. Samples: Because the witness aerogel tile was not of the same batch as the comet tiles, we requested and were allocated 9 aerogel picokeystones cut from the comet tray tiles C2103 and C2061 (Fig. 1). C2061 contains 1 carrot shaped track, as does cell C2103. Location of the tiles can be found at http://wwwcurator.jsc.nasa.gov/stardust/sample_catalog/Cometary /Level3/Level3MosaiccsCometaryTray.pdf. Seven picokeystones were cut from tile C2103, one of these was cut from the top (comet collection side) of the tile and the other 6 were cut from the bottom ( most dense region) of this cell. Two other picokeystones were cut from tile C2061, both from the top of the tile. The picokeystones are triangular shaped, ~ 0.5mm on a side, ~70 microns thick and are sandwiched in between 2 silicon nitride windows and these windows were anchored to our sample mounts using scotch tape. The samples were fedexed overnight to the National Synchrotron Light Source (NSLS) where upon arrival were immediately placed into a nitrogen purged cabinet. Samples are only removed from this cabinet during analysis where they are then kept in a helium purged environment.