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Stardust brings a comet down to Earth
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The aerogel wedge shows a tiny, dense white dot in the upper left quadrant at the end of its trail. This mote of cometary dust, which measures about 10 micrometers or one tenth the diameter of a human hair, entered the sample collector as the craft flew through the tail of comet Wild 2.
PHOTO COURTESY NASA
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The prized cargo weighs less than a grain of salt and would fill no more than a thimble. But the cosmic dust captured by Stardust—NASA’s first mission dedicated to cometary exploration—could shed light on the formation of our solar system, the origins of the Earth and its oceans, even the emergence of life.
After traveling 2.88 billion miles and seven years through deep space, Stardust’s sample canister returned to Earth on January 15, self-parachuting into the Utah desert, from where it was airlifted to safety. Mission scientists, including principal investigator Donald Brownlee (B.S.’65 EECS) and project engineer Peter Tsou (B.S.’65, M.S.’66 EECS), were ecstatic when they finally opened the canister in the clean room at Johnson Space Center in Houston.
“We jumped for joy,” said Tsou. “We knew we’d have particles, but they are much larger than we ever anticipated. We can actually see about two dozen very large ones with the naked eye.” In total, he estimates, Stardust captured thousands more particles, most of them about 10 micrometers, or one tenth the diameter of a human hair.
Launched in February 1999 from Cape Canaveral, Stardust was engineered to achieve a precisely timed rendezvous with comet Wild 2 to collect samples of its dusty tail. On January 2, 2004, the flyby encounter occurred 242 million miles from Earth. The unmanned craft extended its tennis-racket-like collector, laden with a specially formulated silicon medium called aerogel, to capture particles that could be as old as 4.5 billion years.
The stardust has been distributed for extraction and analysis to 150 scientists at laboratories around the world, including Lawrence Berkeley National Lab, where the world’s most powerful electron microscope is being used to examine its chemical composition. The samples will keep scientists busy for decades.
“I fully expect that textbooks in the future will have a lot of information about the formation of the solar system from these samples,” said Brownlee. Some scientists hypothesize that comets first brought water and complex organic compounds—the amino acids and proteins that are the building blocks of life—to Earth billions of years ago.
Also among Stardust’s yield are interstellar dust particles from beyond our solar system, more difficult to visualize than the cometary particles because they are fewer in number and smaller in size. NASA created the stardustathome website for volunteers to help analyze 1.5 million images of particle tracks. Weeks before the images were uploaded, some 100,000 people had already signed up to participate.
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