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Science 15 December 2006
Special Issue devoted to Stardust
Comet Wild 2 originally hails from the Kuiper belt, beyond Neptune, but was recently perturbed into an orbit between Mars and Jupiter that is within the reach of spacecraft. After its launch in 1999, Stardust sneaked up on the comet in 2004, then returned its precious cargo to Earth in a capsule on 15 January 2006. Bringing back materials from a known extraterrestrial source, as with the Apollo samples from the Moon, is critical for deciphering the history of our solar system and interpreting our other extraterrestrial samples: meteorites and cosmic dust particles.
Stardust's goal rested largely on two technical achievements. First the spacecraft had to be slowed so that it could engage with the comet. A clever trajectory enabled it to pass within 240 km of the nucleus at a speed of just 6 km/s, albeit six times faster than a bullet. To catch the comet particles, a special lightweight material called aerogel was developed and molded into a detector grid. Aerogel, the lightest solid known, is a foamed glass that has the density of air (see the cover). Particles were gently brought to a standstill as they tunneled through it without much heating or alteration, leaving carrot-shaped tracks. Thousands of tiny particles were trapped, most of them smaller than a micrometer in size.
Look into the Seeds of Time
Joanne Baker
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