After a seven-year, three-billion-mile expedition through the solar system, NASA’s Stardust spacecraft capsule landed in the Arizona desert on Jan. 15, 2006, with an impressive bounty: a canister full of tens of thousands of comet particles and a smattering of interstellar dust, the first such samples ever collected.
Stardust captured the comet particles from Comet Wild-2 (pronounced Vilt) when the spacecraft flew within 149 miles of it on Jan. 2, 2004, roughly in the vicinity of Jupiter. The spacecraft’s collector swept up particles left in the comet’s wake, preserving them in a silicon material called aerogel, which cushioned and protected the particles on their long journey to Earth.
The Stardust samples offer a time capsule to our primordial past. Comets contain some of the oldest material in the solar system, formed out of the remaining dust and gases left over after the solar system’s creation 4.6 billion years ago. Principal investigator Donald Brownlee has commented that “this has been a fantastic opportunity to collect the most primitive material in the solar system. We fully expect some of the comet particles to be older than the Sun.” Michael Zolensky, another Stardust scientist, offers a vivid sense of how intimately connected comets are to an understanding of life on Earth: “It’s like looking at our great-great grandparents. Much of Earth's water and organics—you know, the molecules in our bodies—perhaps came from comets. So these samples will tell us…basically, where our atoms and molecules came from, and how they were delivered to Earth, and in what amount.”
The samples have already defied their expectations. Some contain minerals that could only have been formed at enormously high temperatures. But comets are icy balls thought to have formed far from the Sun, in the outer, frigid regions of the solar system. Brownlee noted that “when these minerals formed they were either red-hot or white-hot grains, and yet we collected them at a comet [from] the Siberia of the solar system.” According to Zolensky, “It suggests that, if these are really from our own sun, they've been ejected out—ballistically out—all the way across the entire solar system and landed out there.…We can't give you all the answers right now. It's just great we have new mysteries to worry about now.”
About 150 scientists around the world are currently studying the comet samples, while an army of amateur scientists have turned their attention to the stardust also collected during the mission. About 65,000 volunteers from the general public will be enlisted to help find images of interstellar dust embedded in the aerogel. The volunteers of Stardust@home will search images delivered to them on the Internet, using so-called virtual microscopes. While the comet dust is visible to the naked eye, the bits of stardust are only a few microns in diameter. Just 40 to 100 grains of stardust are thought to have been collected, and searching for these particles has been described by the NASA team like “tracking down 45 ants on a football field.”
Fact Monster/Information Please® Database, © 2005 Pearson Education, Inc. All rights reserved.