STARDUST EXTRATERRESTRIAL TYPE OF AIR POLLUTION, STUDY SHOWS\Researchers analyze exotic molecules trapped inside meteors.

Byline: Jane E. Allen Associated Press

Stardust from outside our solar system looks remarkably like the smog found here on Earth, according to a new analysis.

By combining techniques developed at Stanford University in Palo Alto and at Washington University in St. Louis, researchers found that stardust molecules trapped inside meteorites closely resemble familiar air pollutants.

The first laboratory measurements of such extraterrestrial molecules place them in a class of carbon compounds created by partial burning - like diesel exhaust and pollution from smoky barbecues or from natural processes, such as forest fires and volcanic eruptions. Scientists call the compounds polycyclic aromatic hydrocarbons or PAHs.

Among specific carbon molecules that rode to Earth inside meteorites were naphthalene, the chemical in mothballs, and pyrene, a cancer-causing chemical found in charred meat.

The discovery was formally presented recently at the Lunar and Planetary Symposium at Johnson Space Center of the National Aeronautics and Space Administration in Houston.

Stanford graduate student Simon Clemett and Washington University graduate student Scott Messenger said the discovery confirmed observations of scientists who long have believed that their telescopes were picking up chemical signatures resembling PAH compounds in the space between stars.

But what's particularly striking is that the carbon compounds found in stardust were exotic forms of what is found on Earth, said Richard N. Zare, a Stanford chemistry professor who led the team that identified the stardust components. He invented the two-step laser mass spectrometry process used in the chemical analysis.

"The carbon grains clearly are exotic in origin. They're truly far out, they're extraterrestrial, even extrasolar," Zare said in an interview. The stardust particles contained isotopes - or slight molecular variations - of carbon compounds in our atmosphere.

Zare explained that the meteorites trapped particles that stars probably expelled 4.5 billion years ago. By analyzing such particles that reached Earth, "you're in some sense getting your hands on a star."

Furthermore, since the sun is a star formed at the same time as the meteorites, "in some sense we're looking at the same material that went into the sun."

Gerald J. Wasserburg, a geology and geophysics professor at the California Institute of Technology in Pasadena, said the results were "very exciting and deserve a lot of attention."

"One had believed beyond the shadow of a doubt that PAHs were formed around stars, but no direct measurements were made of them," he said.

"And now one has that and that's just wonderful. . . . By looking at these dust grains, which are blown off stars and preserved in meteorites, you are now able to talk about the detailed mechanisms which are taking place in the stars," he said. "You're now doing the nuclear physics of the stars, the nuclear chemistry of the star . . . not by looking at the star, but by looking at the dust grains."

Researchers at Washington University, led by physics professor Robert M. Walker, did the tedious initial work of extracting microscopic grains of graphite from four meteorites. Of 124 grains examined, 89, or 70 percent, showed appreciable concentrations of PAHs, the scientists said.

The research was funded by NASA.