A technician unbolts a canister containing comet dust from the Stardust capsule at Dugway Proving Ground, Utah. The seven-year project collected particles from a comet.(Photo: AP)

    BEIJING, Jan. 19 (Xinhuanet) -- The condition and visibility of comet particles contained inside the tightly sealed Stardust spacecraft that returned to Earth on Sunday surprised NASA's scientists. 

    It's the first time NASA has brought solid material back from space since Apollo 17 delivered 244 pounds of moon rocks in 1972.

    Bill Jeffs, a spokesman for the National Aeronautic and Space Administration (NASA), said that some of the particles were so large they could be seen by the naked eye. He said NASA officials were "ecstatic" and "surprised" by the condition of the particles.

    The largest particles were expected to be no wider than the diametre of a single human hair, and others will be much smaller, NASA scientists said. The material may have to be studied atom by atom.

    The "Stardust" material is from the Comet Wild 2 - a comet that, like most comets, was out of reach for such a retrieval mission until it nearly crashed with Jupiter in 1974, which brought its orbit closer into the sun.

    Steady exposure to solar heat causes most comets to disintegrate after hundreds or thousands of orbits, but Wild 2 was relatively pristine because it has made only five trips nearer to the sun, NASA said.

    Stardust traveled seven years and nearly 3 billion miles, passing within 150 miles of the comet called Wild-2. During the close encounter in 2004, the spacecraft held its tennis-racket-shaped collector in the path of gas and dust shooting from the comet, in the hopes of collecting some cosmic dust.

    But until the collector was opened Tuesday, no one knew whether the device had actually snagged any particles.

    "You just don't know if nature is going to cooperate or not," the mission's principal investigator, University of Washington astronomer Donald Brownlee,said. "It has been a magic mission."

    The capsule tumbled several times when it landed by parachute in the Utah desert, but the impact didn't crack the substance inside, Brownlee said.

    Scientists expect to spend the next decade examining the comet pieces and stardust particles, hoping the research will shed light on the formation of the solar system 4.5 billion years ago. Enditem

   (Agencies)