Scientists’ stardust analysis brings nucleosynthesis full circle

Researchers at Argonne National Laboratory have reached for the stars—and seen what is inside.

Argonne scientists, in collaboration with University researchers and colleagues at Washington University and the Universita di Torino in Italy, examined stardust from a meteorite and found remnants of now-extinct technetium atoms made in stars long ago.

The stardust grains are tiny bits of stars that lived and died before the solar system formed. Each grain is many times smaller than the width of a human hair and carries a chemical record of nuclear reactions in its parent star.

Fifty years ago, famed scientist P.W. Merrill observed the signature of live technetium—an element that has no stable isotopes—in the starlight from certain types of stars, thereby proving the then-controversial theory that stars make atoms via a process called nucleosynthesis. The researchers’ discovery that their stardust grains once harbored live technetium brings the science of nucleosynthesis full circle.

“Finding traces of technetium decay products in stardust provides a very precise confirmation of the theories of how atoms are made inside stars,” said Michael Savina, Argonne scientist and lead author of the research, which was published in the Friday, Jan. 30 issue of Science. “The fact that we can both predict and measure very tiny effects in the chemistry of these grains gives us a lot of confidence in our models of how stars work.”

Authors of the report, in addition to Savina, are Michael Pellin and C. Emil Tripa of Argonne National Laboratory; Andrew Davis and Roy Lewis, Senior Scientists in the University’s Enrico Fermi Institute; Sachiko Amari of Washington University in St. Louis; and Roberto Gallino of the Universita di Torino.

The work was made possible by a specialized instrument at Argonne called CHARISMA, the only instrument of its type in the world.

“CHARISMA is designed to analyze very tiny samples—the kind where you can’t afford to waste atoms because there are so few of them to work with,” Savina said.

The Department of Energy Office of Science and NASA are funding the current upgrade of CHARISMA in anticipation of solar wind samples from the Genesis mission. Scientists believe the solar wind—single atoms and electrically charged particles from the sun—has not changed since the sun was born.

The research group at Argonne will be among the scientists to analyze the samples in an effort to better understand how the planets formed. Current measurements of the sun’s composition are not precise enough to answer key questions about events in the early solar system. The researchers also are preparing to analyze samples from the Stardust mission, which recently captured dust grains from a comet’s tail and will bring them back to Earth in 2006.

The nation’s first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. The University operates Argonne as part of the U.S. Department of Energy’s national laboratory system, and has since Argonne’s creation in 1946.