Organic Molecules Transport Strongest Spectral Signature of Interplanetary Dust Particles

http://www.llnl.gov/pao/news/news_re...-05-01-02.html

Lawrence Livermore National Laboraty News Release
Contact: Anne Stark
Phone: (925) 422-9799
E-mail:

FOR IMMEDIATE RELEASE
January 13, 2005
NR-05-01-02

Organic molecules transport strongest spectral signature of
interplanetary dust particles

LIVERMORE, Calif. - Carbon and silicate grains in interplanetary dust
particles are helping scientists solve a 40-year-old astronomical
mystery.

Using a transmission electron microscope, researchers from Lawrence
Livermore National Laboratory have detected a 5.7-electron volt or 2175
? (angstrom) wavelength feature in interstellar grains that were
embedded within interplanetary dust particles (IDPs). They found that
this feature is carried by carbon and amorphous silicate grains that
are
abundant in IDPs and may help explain how some IDPs formed from
interstellar materials.

The research appears in the Jan. 14 edition of the research journal
Science.

Interplanetary dust particles gathered from the Earth's stratosphere
are
complex collections of primitive solar system and presolar grains from
the interstellar medium. The strongest ultraviolet spectral signature
of
dust in the interstellar medium (the gas and dust between stars, which
fills the plane of a galaxy) is the astronomical 2175 angstrom feature
or "2175 ? bump." Production of this interstellar feature is
generally
believed to originate from electronic transitions associated with the
surfaces of very small grains.

The carbon and silicate grains may have been produced by irradiation of
dust in the interstellar medium. The measurements may help explain how
interstellar organic matter was incorporated into the solar system. In
addition, they provide new information for computational modeling,
laboratory synthesis of similar grains and laboratory ultraviolet
photo-absorption measurements.

"Our finding potentially breaks a log-jam in the search for the carrier
of the astronomical 2175 ? feature," said John Bradley, director of
Livermore's Institute for Geophysics and Planetary Physics and lead
author of the paper. "Over the past 40 years, a whole variety of exotic
materials have been proposed, including nano-diamonds, fullerenes,
carbon 'onions' and even interstellar organisms. Our findings suggest
that organic carbonaceous matter and silicates, the 'common stuff' of
interstellar space, may be responsible for the 2175 ? feature."

Other Livermore scientists on the project include Zu Rong Dai, Giles
Graham, Peter Weber, Julie Smith, Ian Hutcheon, Hope Ishii and Sasa
Bajt.

Outside collaborators include researchers from UC Davis, Lawrence
Berkeley National Laboratory, Washington University and NASA-Ames
Research Center.

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 the University of
California for the U.S. Department of Energy's National Nuclear
Security
Administration.