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"The samples that Stardust returned to Earth are helping rewrite the very history of our solar system," said Don Brownlee, principal investigator for the Stardust mission and a scientist at the University of Washington.
From the day it launched on Feb. 7, 1999, Stardust was a space pioneer. Its launch marked the first U.S. mission focused solely on exploring a comet. The craft was also the first designed to bring back to Earth material from an extraterrestrial source other than the moon.
After nearly five years of hurtling through space, Stardust came within 150 miles (241 kilometers) of the comet Wild 2 (pronounced "Vilt," after its discoverer, Swiss astronomer Paul Wild) on Jan. 2, 2004. As it approached, the craft extended an aerogel-lined collector that looks something like a tennis racket to gather up some of the particles streaming from the comet's coma. The collector was pointed at the comet for about 20 minutes.
Two years later, Stardust had returned for a rendezvous with Earth. As it drew near, it released its sample return capsule, which landed safely on the desert salt flats of Utah. (The Stardust craft itself remains in space -- more on that later.)
Above left: An artist's depiction of Stardust's encounter with the comet Wild 2 in January 2004. (Image credit: NASA/JPL-Caltech)
Right: The comet Wild 2 as viewed by Stardust. (Image credit: NASA/JPL-Caltech)
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- Wild 2 doesn't seem to have the type of comet dust scientists were expecting. In fact, the samples show a closer resemblance to your typical meteorite from the asteroid belt. The dust also contains material believed to have been formed close to the sun during the earliest days of the solar system. The discovery suggests that cosmic material from the asteroid belt can, over time, migrate outward to the distant realm of comets. "It's a reminder that we can't make black and white distinctions between asteroids and comets," said Hope Ishii, a researcher at the Lawrence Livermore National Laboratory. "There is a continuum between them.";
- Stranger still is that Wild 2 shows signs of both ice and "fire." The icy composition of comets has long been accepted, but Stardust researchers have been surprised to find particles of forsterite, a high-temperature silicate material, as well. The mineral is similar to olivine, a component of Hawaii's famous green beaches;
- The complex assortment of materials we're finding in comets suggests the possibility that life originated in space. "All the necessary elements -- clay, organic molecules and water -- are there," said Chandra Wickramasinghe, an astrobiologist at Cardiff University. "The longer time scale and the greater mass of comets make it overwhelmingly more likely that life began in space than on earth."
Above left: Stardust's sample return capsule, which landed on the U.S. Air Force Utah Test and Training Range in Utah. (Image credit: NASA)
Right: Comet particle tracks in aerogel. (Image credit: NASA/JPL)
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Stardust's contributions to our understanding of the solar system recently earned the sample return capsule a spot in the Smithsonian's National Air and Space Museum in Washington: a well deserved rest for something that traveled three billion miles over the course of seven years.
As for Stardust itself? Rather than getting a rest, it's going back to work. Its second mission, dubbed NExT (for New Exploration of Tempel 1), will have it fly to within 120 miles of Tempel 1, the comet that was the target of NASA's 2005 Deep Impact mission. The flyby, expected to occur in 2011, will give researchers a chance to see how a comet changes after a close approach to the sun and possibly also get a glimpse at the crater left behind by Deep Impact (the impact itself created too much dust to make the crater visible).
Repurposing Stardust for the NExT mission is a bargain, too: NASA estimates that the flyby will cost only 15 percent as much as a new mission started from scratch. Talk about recycling on a cosmic scale.!
Above left: A 2-micrometer particle of forsterite captured from the comet Wild 2. (Image credit: NASA/JPL-Caltech/University of Washington)