PASADENA, Calif. – Come Tuesday, February 22, the Stardust spacecraft will attempt to collect the speeding particles of interstellar dust that stream into our solar system from distant stars.

Aerogel is a solid, but the least dense solid known to humans. It is 99.9 percent air and just 0.1 percent silica dioxide, the stuff of glass. Aerogel, however, is 1,000 times less dense than normal glass.

An excellent insulator, NASA used it to keep delicate electronics warm on the Sojourner rover that roamed Mars during 1997’s Pathfinder mission. It has also flown on the space shuttle and on the Mir space station.

On Stardust, engineers have pressed the substance into use as a catcher’s mitt, packing the spacecraft’s dust collector with 260 cubes of the Jell-O-like foam to trap and preserve particles of interstellar and cometary dust.

Jet Propulsion Laboratory scientist Steven Jones said it will be like emptying a gun into a bale of hay when the particles strike the aerogel at a relative speed ranging from 6 to 16 miles (10 to 26 kilometers) a second, leaving a carrot-shaped trail.

"Each particle will crash through this network, literally, of very, very small silica filaments, all of a random length and randomly attached to each other," said Jones, who installed most of the ice cube-sized blocks of aerogel on the collector. "And as the particle goes crashing through them and breaks the filaments it loses kinetic energy and slows down gradually."

The collector will remain passive throughout the experiment, swiveling only slightly every two weeks to receive the full brunt of the dust particles, which will hit it like bugs on a windshield as they flow in from the direction of the constellation Scorpio.

"Except you want to catch the bugs very softly," Atkins said. "This is our butterfly net, if you will."

Atkins said the aerogel is strong, but clear enough so you can trace the tracks left by the streaking particles, allowing them to be extracted once the samples are returned to Earth in 2006.

Aerogel was first discovered in the 1930s. It begins life as a wet gel that undergoes a process called "supercritical drying" that dries it, but leaves its matrix intact.

"It’s the perfect material to capture these particles," Jones said.