Stardust is due to return to Earth with the samples in 2006.

"We reached back in time to collect material that has not been changed for four-and-a-half billion years," said Stardust project manager Tom Duxbury.

The five-meter (16-foot) long probe came within 300 kilometers (186 miles) of the comet, which measures more than five kilometers (3.1 miles) in diameter, at 19H22 GMT, and the first data were received here 22 minutes later, NASA said, revising its previous time frame.

The agency said the flyby occurred at a relative speed of about 22,000 kilometers (14,000 miles) per hour.

"We had to send it into the coma (the gaseous cloud surrounding the comet), getting hit (with dust particles) at six times the speed of a bullet," said Duxbury. "Things could not have worked better."

During the flyby, Stardust's navigational camera took 72 images of the comet and sent them back to NASA's Jet Propulsion Laboratory here. They showed an enormous cratered gray ball of ice and rock, with gaseous jets spitting from some of the craters.

"Nature was really cooperating," said Don Brownlee, the Stardust project's chief researcher. "These are the best pictures ever taken of a comet."

The probe passed through the comet's dust and gas cloud, enabling it to capture particles on its tennis-racket-shaped particle catcher.

NASA said the particle catcher is filled with a material called aerogel, a silicon dioxide substance that is "99.8 percent air, with enough 'give' to slow and stop the particles without altering them radically."

"We have successfully collected samples of a comet and we are bringing them back home," said Brownlee. "Comets preserved the building blocks of our solar system. The mission went fantastically well."

Once the dust particles were snared, the collector folded like a clamshell, securing the samples for a scheduled parachute-assisted landing at the US Air Force Test and Training Range in Utah in January 2006, NASA said.

The specimens will then be sent to the Johnson Space Center near Houston, Texas, for analysis.

The Wild-2 (pronounced Vilt-2) comet, discovered in 1978, is in orbit around the Sun, taking 6.39 years per revolution.

At the end of its mission in two years, Stardust will have covered some four billion kilometers (2.5 billion miles).

From the chemical and physical data contained in the comet's miniscule particles, researchers are hoping to gain clues to the formation of the solar system, the birth of the planets and the matter from which they were formed.

SPACE.WIRE