LOS ANGELES, Jan. 14 (Xinhuanet) -- Hours before the first comet sample return, scientists and officials of the U.S. space agency NASA are gathering in a base in Utah state on Saturday to wait for the finale of a 7-year space Odyssey.

    "I have been waiting 25 years for this time," said Dr. Peter Tsou, the deputy investigator who first put forward the Stardust plan in 1981. Born in China, Tsou is now among the team awaiting the capsule in Utah.

A graphic with information on NASA's Stardust mission. A capsule from the US space probe Stardust is scheduled to parachute to Earth, carrying precious samples of dust collected from stars and comets that scientists hope will shed light on the early solar system. (AFP)

    In a telephone interview with Xinhua, Tsou said the Stardust spacecraft was set to release a capsule carrying dust samples of a faraway comet at about 21:56 Pacific time (0556 GMT Sunday).

    One minute later, springs aboard the spacecraft will literally push the capsule away, putting it into its trajectory toward the Utah Test and Training Range.

    And 15 minutes later, the Stardust spacecraft will perform a maneuver to enter orbit around the sun, while the capsule is set to enter Earth's atmosphere at an altitude of 125 km at 1:57 Pacific time (0957 GMT) Sunday.

    The velocity of the sample return capsule as it enters Earth's atmosphere at 46,440 km per hour will be the greatest of any human-made object on record. This will surpass the record set in May 1969 during the return of the Apollo 10 command module.

    On Saturday morning, the spacecraft crossed the moon's orbit as it makes its way toward Earth, according to Tsou, who is a senior researcher at NASA's Jet Propulsion Laboratory (JPL) based in Pasadena, California.

    The spacecraft has traveled about 4.5 billion km during its seven year round-trip. It is a journey that carried it around the Sun three times and beyond Mars and the asteroid belt -- as far out as half-way to Jupiter.

    This cosmic voyage was designed to trap cometary and interstellar dust particles, which scientists believe will help provide answers to fundamental questions about the origins of the solar system and the life, Tsou said.

    Comets are bodies of dust and ice that accumulated at the edge of the solar system, near Pluto. When they travel close to the Sun, the solar heat causes the ices to sublime and the solar wind pushes the sublimed gases and dust to form a comet's characteristic tail.

    Scientists believe in-depth terrestrial analysis of cometary samples will reveal much not just about comets but about the earliest history of the solar system.

    "Exploring the comet is a very interesting mission, especially the target of our mission, Wild 2," he said. Wild 2, a comet spotted by astronomers first in 1974, is a new visitor to the inner part of the solar system.

    "It has rounded the Sun for just 5 circles, that means, most of its materials are well kept at a pristine state 4.5 billion years ago," Tsou said.

    Stardust, the first NASA spacecraft dedicated solely to the exploration of a comet, was launched on Feb. 7, 1999, from Cape Canaveral, Florida.

    The primary goal of the mission, collecting dust and carbon-based samples during its closest encounter with the comet, was fulfilled as scheduled in January 2004, after nearly four years of space travel.

    In order to capture the dust samples, Tsou also specially designed a medium, a continuous gradient density silica aerogel that is 99.8 percent air and so lightweight it almost floats.

    Particles captured in the aerogel will leave a carrot-shaped trail and be embedded at the tip. The flyby last year has yielded about one-thousandth of an ounce of cometary dust for study, Tsou said.

    Locked within the cometary particles is unique chemical and physical information that could be the record of the formation of the planets and the materials from which they were made.

    "Getting a sample from a comet but not landing on it, is probably the best chance we have of discovering what the solar system was like 4.5 billion years ago," Tsou said. Enditem