WEB EXCLUSIVE

Catch a Comet by the Tail

By Kathy A. Svitil|Wednesday, January 14, 2004
RELATED TAGS: COMETS
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Courtesy JPL/NASA/The Stardust Team

Just two weeks into the new year, NASA has scored two dramatic triumphs—a welcome turnaround from a disastrous 2003. On January 3, the rover Spirit touched down safely on the surface of Mars. One day earlier, the Stardust spacecraft, launched in February 1999, successfully plunged through the dusty and gassy head of comet Wild 2 (pronounced “vilt” in the German style) and scooped up cometary particles that may help reveal our solar system’s mysterious early history. “The samples contain the water and chemical building blocks that formed our solar system, formed the sun, and support life on Earth,” says Stardust project manager Thomas Duxbury of the Jet Propulsion Laboratory in Pasadena, which manages the craft for NASA. “Comets have stayed in the outer fringes of our solar system and have not changed in 4.5 billion years. We went back in time to the beginning of our solar system when we captured those dust particles.”

In addition to collecting fragments of Wild 2, Stardust also obtained 72 stunning high-resolution images, including the most detailed picture ever taken of a comet’s nucleus—the icy, rocky body at the center of a comet’s vast head and tail of evaporated gas and loose dust. One remarkable image of the 3.1-mile-wide nucleus, snapped when the spacecraft was just 311 miles away, reveals a strangely pockmarked, lumpy landscape. “Wild 2 looks different from all other planetary bodies that we have seen,” Duxbury says. Circular depressions that look like typical impact craters are actually vents from which jets of material spew out of the comet as it is heated and vaporized by the sun. Duxbury and his team anticipated such features, he says, “but there were many more jets than we had predicted.”

The comet’s jets also did not behave as expected. Mission planners thought Stardust would encounter a steady stream of particles that increased in intensity as the probe got closer to the comet’s core. Instead, the jets unleashed swarms of particles that blasted into the spacecraft in perilous waves, testing the craft’s defensive shielding. Onboard computers suggest the onslaught of particles breeched Stardust’s outer layer of shielding on at least 10 occasions, although the probe’s other shields held firm. Meanwhile, a tennis-racket-shaped collector filled with an ultra-low density glass foam called aerogel flipped out of the craft and captured about one ounce of the fast-moving dust, which was then stowed away in a return capsule.

Now comes the agonizing part: Duxbury and his colleagues will have to sit tight until January 15, 2006 to get their hands on a piece of comet Wild 2. On that day, Stardust will fly past Earth and drop its payload, which will then make a parachute landing in the Utah desert. This package of comet stuff, the first sample of material ever returned from deep space, will allow a hands-on look at the chemistry of the early solar system. Duxbury is betting it will be worth the wait.

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