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Scientists Get First Look at Recently Returned Star Dust Grains

Scientists are elated at the samples of star dust returned to Earth by an American spacecraft Sunday. They have gotten their first look inside the canister bearing the grains and have pronounced the seven-year mission to gather them a huge success.

Mission scientists at NASA's Johnson Space Center in Houston have opened the canister bearing the particles collected by the U.S. Stardust spacecraft. The probe captured dust grains expelled by comet Wild-2 in 2004 after a five-year journey to meet it and returned them to Earth Sunday by dropping a capsule that parachuted onto the Utah desert.

Comets are dusty balls of ice that orbit the sun and are considered remnants of solar system formation 4.5 billion years ago. The dust particles from inside them are thought to be uncontaminated leftovers that can reveal the chemical secrets of the developing solar system.

The mission's principal investigator, University of Washington astronomer Donald Brownlee, says the dust collection exceeds all expectations. He saw lots of grains captured by the spacecraft's collecting grid, and calculates that there may be a million of them.

"The particles, perhaps up to a million particles from the comet, are embedded in this," he said. "So this is our treasure trust, samples from the birth of the solar system are contained in this grid."

The grid contains a remarkably wispy fiberglass material called aerogel that is as much as 99.9 percent empty space. The aerogel trapped the dust grains as the comet expelled them during a melting phase on its trip from the outer reaches of the solar system in toward the Sun.

"This is an incredible material," he said. "We actually got into the Guinness Book of World Records for developing this particular aerogel as the world's lowest density solid."

Brownlee says the aerogel greatly reduced the stress of impact on the particles, helping preserve them in their original condition. He adds that tracks of the largest particles are visible in the material from several meters away, with one track a tiny tunnel almost large enough to fit a little finger.

Brownlee points out that, as small are the particles are, they are still too large for highly sensitive analytical tools to study them, so they must be cut into many smaller pieces.

"We actually think of these as huge rocks because these particles are actually made out of collections of tens of thousands of much, much smaller particles," he explained. "In fact, when we get one of these particles, it's actually too big for us to work on and we slice it up into hundreds of different samples we really want to get. Those samples are the actual original building blocks of the solar system."

The Johnson Space Center is the curator of the cosmic dust. As many as 150 scientists worldwide are waiting to study them.