AeroGel

This guy here is Peter Tsou. He's a scientist at NASA's Jet Propulsion Laboratory, and he's holding an amazing substance called aerogel. Aerogel is a solid, but it is 99.8% empty space. In fact, it very closely approaches the density of air. It practically IS air. It's still a solid, though, and you can even pick it up or set things on it.

Since it's very porous, if you throw something at it, it will bury itself within the material. Like this:

This substance was recently used aboard the Stardust spacecraft, which flew through through the trail of a comet and collected dust particles. Since the dust in the comet's trail was traveling at about 6 times the speed of a rifle bullet, the only way to collect them without altering their shape or destroying them was to use this substance. As an added benefit, objects embedded in the substance leave that nice little trail, so no matter how small the particle is, it'll still be pretty easy to find and retrieve. And also, it doesn't conduct heat very well, so you can do things like this:


Or this...


Aerogel was recognized by Guinness World Records in 2002 as the world's least dense solid. Stardust successfully completed its mission on January 2nd of this year, and is currently headed home. Its return date is January 2006.


Linkage:

http://stardust.jpl.nasa.gov/photo/aerogel.html
http://stardust.jpl.nasa.gov/tech/aerogel.html
http://stardust.jpl.nasa.gov/overview/faq.html