Comet Catcher.

An intergalactic dust-buster? Meet Stardust, NASA's latest high-tech spacecraft (above). Launched earlier this year, Stardust will collect and bring cometary dust back to Earth for detailed study.

The Stardust mission should further scientists' understanding of the history of the solar system and even life on Earth. Many researchers think comets may contain the original materials that formed the sun and planets. Some even think cometary debris raining down on early Earth "may potentially have played key roles in the origin of life," says researcher Scott Sandford at NASA's Astrochemistry Lab in California.

But keeping up with a swift comet is tricky. Comets, huge balls of ice and dust, travel at speeds of up to 9,000 m (30,000 ft) per second--about 10 times faster than a speeding bullet! How will Stardust make the catch?

Enter Aerogel, a type of foam that looks like a solid chunk of blue smoke. Aerogel is composed of pure silica, the same material that makes up glass and sand. The foam's atomic structure looks like a fishnet, explains Peter Tsou of the Jet Propulsion Lab in California. In fact, Aerogel's structure is so unique, it's 99.8 percent air--the lowest density (mass per unit volume) of any solid!

To make Aerogel an effective comet catcher, Tsou altered the foam's density. The front portion of the 3-cm-thick Aerogel is much less dense than the back. So when a speedy particle hits the front of the foam, the particle will slow down without breaking up on impact (see inset above).

Stardust will meet up with Comet Wild-2 in 2004 outside Mars' orbit. Stardust will swoop through Wild-2's coma, or gaseous head, collecting tiny dust particles with the Aerogel. The space dust-buster will then drop its comet samples back on Earth in 2006.