Aerogel will be used on the STARDUST spacecraft to capture comet particles from Comet Wild 2. The pics are amazing. They look fake, but they come from the NASA web site.
To collect particles without damaging them, Stardust uses an extraordinary substance called aerogel. This is a silicon-based solid with a porous, sponge-like structure in which 99.8 percent of the volume is empty space. By comparison, aerogel is 1,000 times less dense than glass, which is another silicon-based solid. When a particle hits the aerogel, it buries itself in the material, creating a carrot-shaped track up to 200 times its own length. This slows it down and brings the sample to a relatively gradual stop. Since aerogel is mostly transparent – with a distinctive smoky blue cast – scientists will use these tracks to find the tiny particles.