Cosmic stardust detectives

We’re all made of stardust, Joni Mitchell once sang, and technically, she was right. Like giant nuclear ovens, stars cook up almost all of the elements in the periodic table, expelling them after the star’s death. A stream of this interstellar dust, which makes up our homes, cars, even our bodies, flows through space. For the first time, scientists say they may have recovered some, with the help of one Canadian space buff.

Back in 1999, NASA’s Stardust spacecraft was launched. Shaped a bit like a tennis racket, this collector was outfitted with blocks of aerogel—a ghostly blue-white material, similar to glass but only a few times denser than air, in which particles bury themselves upon impact. The Stardust mission was designed to fetch samples from an ancient comet containing the “best-preserved samples of the building blocks of our solar system,” says Don Brownlee, a cosmic dust expert at the University of Washington, its principal investigator. “As a bonus,” he says, “we used the backside of the collector to gather dust flowing in from the galaxy.” The Stardust collector returned to earth in 2006, bringing the first solid samples ever retrieved from beyond the moon.

In the lab, comet particles were easy enough to find, Brownlee says; visible to the naked eye, they leave long tracks in aerogel “like hollow carrots.” But tiny interstellar dust particles are another story. Researchers considered making a computer program to seek them out, but soon noticed that people—even untrained ones—did better. Inspired by other crowdsourcing efforts, Andrew Westphal of the University of California, Berkeley created Stardust@home, an Internet application where the public could sift through images of aerogel for signs of interstellar dust tracks. Since it was launched in 2006, more than 27,000 people (so-called “dusters”) joined in, completing over 71 million searches. Altogether, 28 tracks have been found.

One of those tracks—maybe the most promising one—was pinpointed by Bruce Hudson of Midland, Ont. A former groundskeeper, Hudson, now 47, had to leave his job after suffering a stroke in 2003. Surfing the Net one day, he came across Stardust@home, and was quickly hooked. “Some days, I’d do four or five hours [of dusting],” he says. “Other days, I could go up to 15.” In 2007, Hudson found what looked like a track, and submitted it. It wasn’t until a few weeks ago that he heard back from Westphal: it seems very likely Hudson found something. For one thing, while most other tracks are angled in a way that suggests they were created by debris from the spacecraft, Westphal says, his “is coming from the right direction” to have been created by stardust. Remarkably, it contained two particles, which Hudson named Sirius and Orion. “It’s pretty amazing to find something so rare,” Hudson says. Upon announcing the discovery earlier this month, Westphal told the BBC, “if we drop [this particle] on the floor, it will cost $300 million to get another one.”

Once Sirius and Orion are confirmed to be bits of stardust—which Brownlee believes they will—their research value will be phenomenal. “You’re getting a piece of the Milky Way galaxy in your hands,” says Brownlee. Interstellar dust could teach us something about galactic evolution, he says, and something about ourselves, too, says Westphal: “We’re like people who study ancient fossil hominids, like Lucy. This is the stuff the solar system is made of, and the planets—and us.”