[meteorite-list] Stardust Formed Close To Sun

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 4 Jan 2008 15:06:21 -0800 (PST)
Message-ID: <200801042306.PAA15775_at_zagami.jpl.nasa.gov>

https://publicaffairs.llnl.gov/news/news_releases/2008/NR-08-01-01.html

News Release

Contact: Anne M. Stark
Phone: (925) 422-9799
E-mail: stark8 at llnl.gov

FOR IMMEDIATE RELEASE
January 3, 2008
NR-08-01-01

Stardust formed close to sun

LIVERMORE, Calif. -- Samples of the material picked up during the NASA
Stardust mission indicate that parts of the comet Wild 2 actually formed
in an area close to the sun.

New research by an international collaboration including Livermore
researcher Sa??a Bajt analyzed noble gases within Stardust samples.The
helium and neon isotope analysis suggests that some of the Stardust
grains match a special type of carbonaceous material found in
meterorites; hence both must have spent time in the same gas reservoir,
which was close to the sun.

About 10 percent of the mass of Wild 2 is estimated to be from particles
transported out from hot inner zones to the cold zone where Wild 2
formed. The paper concludes that this is how these grains with unusual
isotope ratios go incorporated into a comet.

Earlier research showed that the comet formed in the Kuiper Belt,
outside the orbit of Neptune, and only recently entered the inner
regions of the solar system.

Wild 2 spent most of its life orbiting in the Kuiper Belt, far beyond
Neptune, and in 1974 had a close encounter with Jupiter that placed it
into its current orbit. The Stardust spacecraft's seven-year mission
returned to earth in January 2006 with particles that are the same
material that accreted along with ice to shape the comet about 4.57
billion years ago, when the sun and planets formed.

But during its lifetime, Wild 2 gathered material that formed much
closer to the sun.

And the new research, which appears in the Jan. 4 issue of the journal
Science, shows that some of the particles in Stardust are consistent
with the early solar nebula.

"The unusual isotope ratio of helium and neon demonstrate that materials
in comet Wild 2 had been much closer to the young sun than previously
expected," Bajt said.

Bajt, who studied tracks in aerogel caused by cometary particles rich in
noble gases, used infrared spectroscopy, which is very sensitive in
detecting organic molecules. She found none, at least not in the pieces
of aerogel she examined. The group concluded that the carriers of the
noble gases must be the refractory metal-metal sulfide-metal carbide
grains, unlike what many expected would be a meteoritic Q-phase, which
is known to be organic.

"That's the first-order finding of the paper, and it's a rather
startling one," said lead author Robert Pepin from the University of
Minnesota.

The second conclusion is that the ion irradiation is the only known
mechanism that could load the grains (by ion implantation) to the very
high concentrations based on mass density estimates from X-ray
absorption spectroscopy by Andrew Westphal and his team at the (Space
Science Laboratory, UC Berkeley.

Noble gases are excellent tracers of contributions from various solar
system volatile reservoirs and of physical processing of gases acquired
from these reservoirs. Their elemental and isotopic compositions in
primitive meteorites differ from those in the Sun. Planetary atmospheres
display noble gas signatures distinct from both solar and meteoritic
patterns.

X-ray absorption spectroscopy in the current study showed that the
grains are composed primarily of high-temperature metal.

The X-ray and isotopic analyses point to gas acquisition in a hot,
high-ion flux nebular environment close to the young sun.

Stardust is a part of NASA's series of Discovery missions and is managed
by the Jet Propulsion Laboratory. Stardust launched in February 1999 and
set off on three giant loops around the sun. It began collecting
interstellar dust in 2000 and met Wild 2 in January 2004, when the
spacecraft was slammed by millions of comet particles, nearly halting
the mission. It is the first spacecraft to safely make it back to Earth
with cometary dust particles in tow.

Founded in 1952, Lawrence Livermore National Laboratory is a national
security laboratory, with 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 Lawrence Livermore
National Security, LLC for the U.S. Department of Energy's National
Nuclear Security Administration.
Received on Fri 04 Jan 2008 06:06:21 PM PST