[meteorite-list] Murchison Meteorite Grains Divulge Earth's Cosmic Roots

[Ron Baalke]

http://news.uchicago.edu/news.php?asset_id=1633

Meteorite grains divulge Earth's cosmic roots
The University of Chicago
June 16, 2009

The interstellar stuff that became incorporated into the planets and
life on Earth has younger cosmic roots than theories predict, according
to the University of Chicago postdoctoral scholar Philipp Heck and his
international team of colleagues.

Heck and his colleagues examined 22 interstellar grains from the
Murchison meteorite for their analysis. Dying sun-like stars flung the
Murchison grains into space more than 4.5 billion years ago, before the
birth of the solar system. Scientists know the grains formed outside the
solar system because of their exotic composition.

"The concentration of neon, produced during cosmic-ray irradiation,
allows us to determine the time a grain has spent in interstellar
space," Heck said. His team determined that 17 of the grains spent
somewhere between three million and 200 million years in interstellar
space, far less than the theoretical estimates of approximately 500
million years. Only three grains met interstellar duration expectations
(two grains yielded no reliable age).

"The knowledge of this lifetime is essential for an improved
understanding of interstellar processes, and to better constrain the
timing of formation processes of the solar system," Heck said. A period
of intense star formation that preceded the sun's birth may have
produced large quantities of dust, thus accounting for the timing
discrepancy, according to the research team.

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*Citation:* "Interstellar Residence Times of Presolar Dust Grains from
the Murchison Carbonaceous Meteorite," /Astrophysical Journal/, June 20,
2009, Vol. 698, Issue 12, pages 1155-1164

*Authors:*
Philipp R. Heck, University of Chicago Department of Geophysical
Sciences and Chicago Center for Cosmochemistry

Frank Gyngard, Laboratory for Space Sciences and Physics Department,
Washington University, St. Louis

Ulrich Ott, Max Planck Institute for Chemistry, Mainz, Germany

Matthias M.M. Meier, Institute of Isotope Geology and Mineral Resources,
Zurich, Switzerland

Janana N. Ãvila, Research School of Earth Sciences and Planetary
Science Institute, Australian National University, Canberra

Sachiko Amari, Laboratory for Space Sciences and Physics Department,
Washington University, St. Louis

Ernest K. Zinner, Laboratory for Space Sciences and Physics Department,
Washington University, St. Louis

Roy S. Lewis, Enrico Fermi Institute and the Chicago Center for
Cosmochemistry, University of Chicago

Heinrich Baur, Institute of Isotope Geology and Mineral Resources,
Zurich, Switzerland

Rainer Wieler, Institute of Isotope Geology and Mineral Resources,
Zurich, Switzerland

*Funding sources:* National Aeronautics and Space Administration, Swiss
National Science Foundation, the Australian National University, and the
Brazilian National Council for Scientific