NASA's Stardust probe returned to Earth last weekend loaded with primordial debris from an ancient comet, researchers said today, providing an unprecedented glimpse into the birth of the solar system 4.6 billion years ago.

Now inside an ultra clean room at the Johnson Space Center in Houston, the Stardust sample return canister has been opened up to give scientists their first glimpse inside.

"It exceeded all of our grandest expectations," said principal investigator Don Brownlee. "There are many things you can worry about on a mission like this and it's a magic moment when basically everything in this project, including the comet, came through.

"The spacecraft had to perform as it was designed to do. We didn't know about the comet, we have no control over nature, but the comet produced the samples that we wanted and the samples were of a nature that they could be collected."

The Stardust probe began its seven-your voyage Feb. 7, 1999, with a flawless launch from the Cape Canaveral Air Station in Florida atop a Boeing Delta 2 rocket.

The target of the mission was comet Wild 2, which spent virtually its entire life in the outer solar system. In 1974, however, the comet made a close flyby of Jupiter, which deflected it into a different orbit that has since carried it around the sun only a handful of times. Compared to other short-period comets, Wild-2 is believed to be relatively pristine, providing an unprecedented window on the birth of the solar system.

After a velocity-boosting Earth flyby in 2001, Stardust finally caught up with the comet on Jan. 2, 2004. Just before closest approach, a two-sided 14-inch-wide dust collector shaped like a tennis racket was extended into the dust stream surrounding the comet. Cells on the back side of collector were used earlier in the flight to collect interstellar dust grains.

Along with successfully collecting samples, the spacecraft's navigation camera snapped 72 photos of Wild-2's frozen nucleus as the spacecraft made its final approach.

The goal of the ambitious mission is to answer long-standing questions about the cloud of dusty debris that coalesced to form the solar system and whether comets helped seed planet Earth with water and the organic building blocks of life.

Wrapping up its seven-year, 2.9-billion-mile space odyssey, the Stardust sample return vehicle plunged back to Earth early Sunday, slamming into the atmosphere above the western United States at nearly 30,000 mph before floating to a gentle, parachute landing in Utah. The canister was collected, flown to Houston and opened two days later.

The comet fragments were captured in a material called aerogel, an ultra low-density glass-like substance sometimes referred to as "frozen smoke." Particles hitting aerogel at high speeds burrow into the material leaving a cone-shaped track behind.

"I had warned the team we might not be able to see tracks with the naked eye and not to be disappointed," Brownlee said. He need not have worried. The aerogel features numerous easy-to-see tracks, including at least one large enough to poke a finger in.

"The prediction was that we would get a dozen particles larger than human hair size and one particle a little bit larger than a millimeter," Brownlee said. "I think we've probably got that. ... We were totally overwhelmed by the ability to actually see this stuff so straight forwardly. ... Just looking at it, you can see hundreds and hundreds of tracks."

He said investigators now expect to find more than a million particles larger than one-millionth of a meter across.

"At this point in time, we're absolutely thrilled," Brownlee said. "All the things that can go wrong in space or scientifically, none of the bad things happened and it really exceeded our wildest expectations."

More than 150 scientists around the world will study the comet fragments to specify their bulk composition, mineralogy, petrology, spectroscopic properties and whatever organic compounds might be found.

Brownlee said Stardust cost American taxpayers some $200 million over the past decade, adding with a laugh, "the way I like to look at it, it's the same cost as a well-paid baseball player over a 10-year period."

He said "the fundamental result of this is knowledge. Right now, you go to new astronomy textbooks and they have pictures of the comet we took two years ago. So our mission has already changed the concept of comets. We now have samples from the very edge of the solar system.

"NASA's launching a Pluto mission right now and it's kind of an interesting link," he said. "New Horizons is going to Pluto. We have a sample right now here in Houston of a body that formed in the same collection of bodies that Pluto is a member of, the Kuiper belt. We have samples from the edge of the solar system. "For all the ideas and theories people might have, we have some real ground truth, we have actual samples of the materials the solar system was formed from." Initial scientific results from the Stardust mission are expected to be presented in March.

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