Counting atoms that aren’t there, in stars that no longer exist

Researchers at the U.S. Department of Energy’s Argonne National Laboratory
have reached for the stars – and seen what’s inside.

Argonne scientists, in collaboration with colleagues at the University of
Chicago, 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.

Famed scientist P.W. Merrill fifty years ago 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 the lead author on the research,
which is published today in 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 on the report, in addition to Savina, are Michael Pellin and C. Emil
Tripa of Argonne, Andrew M. Davis and Roy S. Lewis of the University of
Chicago, Sachiko Amari of Washington University in St. Louis, and Roberto
Gallino of Universita di Torino in Italy. Funding was provided by the U.S.
Department of Energy Office of Science, the University of Chicago, NASA, and
the Italian FIRB Progetto Origine Astrofisica degli Elementi Pesanti Oltre
il Ferro.

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.

CHARISMA is presently being upgraded, with funding from the Department of
Energy Office of Science and from NASA, in anticipation of samples from the
Genesis mission to collect samples of the solar wind – single atoms and
electrically charged particles from the sun – which scientists believe
hasn’t 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 are also
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.