Word: dust
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Dates: during 1990-1999
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...spectral magnificence, the tail of a comet is about as close as you can get to nothing at all, a banner of dust so tenuous that a cubic mile's worth wouldn't fill a shoebox. Yet that near nothingness holds many secrets. Comets are leftovers from the creation of the solar system 4.5 billion years ago; they also delivered organic chemicals and water--the crucial building blocks of life--to the young Earth. Scientists would love, therefore, to get a bit of comet into the lab for analysis...
...looks as though they will. On Feb. 6 a remarkable space probe called Stardust is scheduled to take off for a January 2004 encounter with Comet Wild (pronounced Vilt) 2. With a tennis racquet-size collector, Stardust will snatch dust particles from the comet's tail as it flies by and then, in an audacious interplanetary maneuver, return to parachute its precious cargo to Earth two years later...
...ingenious. Although the probe will loop two times around the sun to help it match orbits with the comet, Stardust and Wild 2 will still shoot past each other at nearly 4 miles per second, 10 times as fast as a speeding bullet. In order to catch dust particles without disintegrating them, Jet Propulsion Lab engineer Peter Tsou first thought of making a trap out of Styrofoam; he figured dust would bury itself harmlessly inside. Unfortunately, says Tsou, "cosmic dust particles are so small that on Styrofoam, I wouldn't be able to see them...
...switched to aerogel, an ultra-lightweight glass foam that's 99.8% air. It resembles nothing so much as solidified smoke. The aerogel is packed into a collector that resembles a circular ice-cube tray about a foot across. En route to Wild 2, one side will trap dust that's wafting in from beyond the solar system--another item of great interest to astronomers--and once there, it will flip to scoop up comet dust...
...particles, some of which will be smaller than the width of a human hair, but they expect to have it down by 2006. They may not have the luxury of a pure sample: a perfect seal would have been too expensive, which leaves a remote chance that some earthly dust could contaminate the aerogel on re-entry, making analysis more complicated...