The Stardust spacecraft passed close to the nucleus of Comet Wild II in January 2004 and returned to Earth in 2006. It had collectors made of aerogel, a spongy glass of density lighter than air for trapping particles released from the comet.
The spacecraft passed the comet at 6km/s so dust and grains evaporated from the comet nucleus impacted into the aerogel with this speed. The grains left impact tracks, generally ‘carrot-shaped’ where the shock of impact into the aerogel blows a large cavity in the aerogel but narrows as the grain slows down to end up with the grain at the point of the ‘carrot’. More volatile-rich particles rapidly boiled off their volatiles and broke up, ejecting fragments in all directions. These left tracks that were more ‘bulbous’ and contained tracks with particles at high angles to the original incoming grain direction.
Stardust at Manchester
We are analysing xenon, krypton, organic molecules and volatile elements along the inside of the walls using our unique instruments RELAX and .
We are currently in the process of incorporating Closed System Stepped Etching (CSSE) with RELAX, with the hope of being able to separate out implanted cometary xenon from the high levels of background xenon trapped in the aerogel. This technique will allow us to dissolve away the silicate aerogel by passing a HF vapour over in it vacuo. The gas released will be analysed for any cometary xenon component. The residual, more robust organic, metal and silicate particles trapped from the comet will then be analysed by step heating.
We are using C60-TOFSIMS to analyse the surface of the tracks to look for organic molecules and volatile elements trapped in the walls of the track by the grain as it exploded its way into the aerogel. Because of the spongy nature of the aerogel, these analyses are very tricky as the organic material diffuses into the walls and the aerogel tiles are contaminated with organic material from the production process already. We therefore use "blanks" from the backside of the tiles and from un-flown tiles to subtract this blank. First results have been presented at conferences as the work is still on-going [1,2].
Additionally, we started a collaboration with the University of Kent to study the survival of organic material in 6km/s impacts into Al-foil . Al-foil was placed between the aerogel tiles and the structure for easier removal of these tiles but turned out to be an excellent capture medium on its own. The only downside is the high impact velocity into relative hard Al-foil which can alter the organic material which is why we started to study how organic material is altered during impact.
 Henkel, T. and I. Lyon. Further Analysis of the Molecular Structure of Cometary Organic Material. in Lunar and Planetary Science Conference. 2013.
 Rost, D., T. Henkel, and I. Lyon, Analysis of Sectioned Aerogel Tracks of Comet Wild 2 Particles with C60-ToF-SIMS. Meteoritics and Planetary Science Supplement, 2011. 74: p. 5402.
 Henkel, T., et al. Survival of Organic Compounds on Al Foil Under Stardust Conditions. in Lunar and Planetary Institute Science Conference Abstracts. 2012.