[meteorite-list] Livermore Lab Physicist Date Lifetime of Solar Nebula at Two Million Years

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Apr 20 17:40:15 2005
Message-ID: <200504202112.j3KLCN506431_at_zagami.jpl.nasa.gov>

http://www.llnl.gov/pao/news/news_releases/2005/NR-05-04-02.html

Lawrence Livermore National Laboratory News Release
Contact: Anne M. Stark
Phone: (925) 422-9799
E-mail: stark8_at_llnl.gov

FOR IMMEDIATE RELEASE
April 20, 2005
NR-05-04-02

Livermore Lab physicist dates lifetime of solar nebula at two million years

LIVERMORE, Calif. - The oxygen and magnesium content of some of the
oldest objects in the universe are giving clues to the lifetime of the
solar nebula, the mass of dust and gas that eventually led to the
formation of our solar system.

[image]
Specimen from the Allende Meteorite
Researchers analyzed the calcium aluminum-rich inclusion (CAI), the
larger circular object in the center of the photo, and the chondrule,
the smaller circular object on the left, in a hand specimen of the
Allende meteorite.

By looking at the content of chondrules and calcium aluminum-rich
inclusions (CAIs), both components of the primitive meteorite Allende,
Lab physicist Ian Hutcheon, with colleagues from the University of
Hawaii at Manoa, the Tokyo Institute of Technology and the Smithsonian
Institution, found that the age difference between the two fragments
points directly to the lifetime of the solar nebula.

CAIs were formed in an oxygen-rich environment and date to 4.567 billion
years old, while chondrules were formed in an oxygen setting much like
that on Earth and date to 4.565 billion, or less, years old.

"Over this span of about two million years, the oxygen in the solar
nebula changed substantially in its isotopic makeup," Hutcheon said.
"This is telling us that oxygen was evolving fairly rapidly."

The research appears in the April 21 edition of the journal Nature.

One of the signatures of CAIs is an enrichment of the isotope Oxygen 16
(O-16). An isotope is a variation of an element that is heavier or
lighter than the standard form of the element because each atom has more
or fewer neutrons in its nucleus. The CAIs in this study are enriched
with an amount of O-16 4 percent more than that found on Earth. And,
while 4 percent may not sound like much, this O-16 enrichment is an
indelible signature of the oldest solar system objects, like CAIs. CAIs
and chondrules are tens of millions of years older than more modern
objects in the solar system, such as planets, which formed about 4.5
billion years ago.

"By the time chondrules formed, the O-16 content changed to resemble
what we have on Earth today," Hutcheon said.

In the past, the estimated lifetime of the solar nebula ranged from less
than a million years to ten million years. However, through analysis of
the mineral composition and oxygen and magnesium isotope content of CAIs
and chondrules, the team was able to refine that lifespan to roughly two
million years.

"In the past the age difference between CAIs and chondrules was not
well-defined," Hutcheon said. "Refining the lifetime of the solar nebula
is quite significant in terms of understanding how our solar system
formed."

Founded in 1952, Lawrence Livermore National Laboratory has a mission to
ensure national security and apply science and technology to the
important issues of our time. Lawrence Livermore National Laboratory is
managed by the University of California for the U.S. Department of
Energy's National Nuclear Security Administration.
Received on Wed 20 Apr 2005 05:12:22 PM PDT