Astronomer Don Brownlee's third floor office is cluttered with space paraphernalia, much of it tinged with a whiff of nostalgia for past triumphs: a piece of insulating tile from the first space shuttle flight; a plaque from the first U.S. satellite; models of pioneering solar-system probes. On the walls there is a gorgeous painting of Halley's comet floating over Antarctica in 1986, along with a whimsical illustration of an Apollo-era astronaut on the moon, gazing at Earth and urinating in a graceful arc onto lunar soil.
But one item—a nearly invisible block of stuff on a shelf next to an orange Slinky—points squarely to the future. This strange translucent cube has a faint blue sheen, like a frozen puff of cigarette smoke, and an inch-wide piece of it feels as light as air. It crumbles when I squeeze it, coating my fingertips with something that feels like sticky talcum powder. Brownlee says this chunk of almost-nothing is called aerogel and that a piece of it the size of a person would weigh less than a pound. It feels weirdly adhesive because it consists of countless loosely clumped clusters of silica dioxide molecules, essentially tiny bits of glass. "You'll inhale some particles, and your mouth will taste funny," Brownlee warns, just as a dry metallic taste hits me.
Much larger cubes of aerogel are 205 million miles from Earth, flying aboard a remarkable NASA spacecraft called Stardust. The probe, which Brownlee oversees from the University of Washington in Seattle, is hurtling toward a meeting with comet Wild 2 (pronounced in the German fashion as "vilt" 2). Aerogel and Wild 2 should meet each other this January. When Stardust flashes past, dust shed from the comet will strike the aerogel at a speed some six times that of a rifle bullet. The aerogel will snare the particles, and two years later Stardust will return to Earth. The precious payload—comet flecks embedded in aerogel and protected by a heat-resistant casing—will parachute to the desert floor in Utah.
