Stardust Reveals Clues About Solar System’s Past

Four years ago, NASA's Stardust spacecraft did something remarkable. It chased down a comet and collected grains of dust blowing off its nucleus. The studies of cometary dust are part of a larger effort to trace the history of our solar system. Planetary scientists regard comets as the most pristine remnants of the ancient cloud of gas and dust that condensed into the sun and the myriad bodies that orbit it.

Samples of the comet dust were shipped to scientists all over the world to analyze its makeup. University physics professor Bob Pepin and his colleagues found evidence that after being generated near the infant sun, the gases blasted their way into nearby dust particles, which appeared in the journal Science.

"We want to establish what the solar system looked like in the very early stages," says Pepin. "If we establish the starting conditions, we can tell what happened in between then and now." One early event was the birth of Earth's moon, about 50 million years after the solar system formed, he says.

Also, the gases he studies have relevance even closer to home.

"Because some scientists have proposed that comets have contributed these gases to the atmospheres of Earth, Venus, and Mars, learning about them in comets would be fascinating," he says.

"Somehow these little high-temperature particles were transported out very early in the life of the solar system," he explains. An idea circulating among physicists is that the particles were hurled outwards ballistically from somewhere close to the young sun. If this really happened, it could have played a major role in shaping the solar system.

Livermore researcher Sasa Bajt was also part of the international team that analyzed the comet dust. Bajt found that the helium and neon isotope analysis suggest that some of the Stardust grains match a special type of carbonaceous material found in meteorites. This would suggest that both must have spent time in the same gas reservoir, which was close to the sun. About 10 percent of the mass of Wild 2 is estimated to be from particles transported out from hot inner zones to the cold zone where Wild 2 formed. The paper concludes that this is how these grains with unusual isotope ratios got incorporated into a comet. Earlier research showed that the comet formed in the Kuiper Belt, outside the orbit of Neptune, and only recently entered the inner regions of the solar system.

The comet Wild 2 spent most of its life orbiting in the Kuiper Belt, far beyond Neptune, and in 1974 had a close encounter with Jupiter that placed it into its current orbit. The Stardust spacecraft’s seven-year mission returned to earth in January 2006 with particles that are the same material that accreted along with ice to shape the comet about 4.57 billion years ago, when the sun and planets first formed. Looking at these materials is like having a window to a much younger version of our Solar System.

Posted by Rebecca Sato

Links:

http://www1.umn.edu/umnnews/Feature_Stories/A_speck_of_Stardust2C_a_window_on_the_young_solar_.html
https://publicaffairs.llnl.gov/news/news_releases/2008/NR-08-01-01.html