A NASA scientist told Chinese audience on Thursday that his team had tested more than 50 comet dust samples captured by the "Stardust" capsule and a preliminary report will be released in September.

Stardust's mission began in 1999, circumnavigating the sun three times and traveling halfway to Jupiter to collect particles from comet Wild 2 in January of 2004. The dust was captured by a space probe shaped like a tennis racket which contained ice cube-sized compartments lined with aerogel.

The Stardust capsule fell to Earth on Jan. 19 this year after a seven-year journey in which it traveled 4.63 billion kilometers.

"We found that none of the particles are identical and we also came across some unknown materials," said Dr. Peter Tsou, deputy chief investigator of NASA's Stardust mission, at the on-going 36th Committee on Space Research (COSPAR) Scientific Assembly in Beijing.

"This is the first time a human eye has seen comet dust, and it may help us to find clues on how the solar system formed," Tsou said.

The American with Chinese origin also donated 14 "aerogel" samples to the Chinese Academy of Sciences. These samples resemble the gel, a sponge-like substance carried on the spacecraft, which is essential to catch the dust.

"We expected to find materials like ice instead of high-temperature substances on Mars, which is considered a very cold celestial body, but we found one of the dust samples was formed at a temperature of 1700 degrees Celsius," Tsou said. "It seems we have much more to learn about the solar system."

The Earth could not preserve samples from more than four billion years ago after experiencing acute weather and countless volcanic eruptions. However the comet could do it by traveling in a marginal area of the solar system with a very low temperature, Tsou said.

"The spacecraft brought back a satisfactory amount of samples and a lot of them could be seen with the naked eye," Tsou said.

When the spacecraft meets a comet, the speed of the comet particles could be twenty to forty times faster than a bullet fired from a rifle, so only this kind of gel could collect the particles, without changing their shape and chemical compositions, according to Tsou.

"We may need another 20 years to form a clear understanding of these samples because we have only studied a small part of what we have, but we plan to submit a preliminary report this September," Tsou said.

(Xinhua News Agency July 21, 2006)