[meteorite-list] Comet Dust Holds Building Blocks of Life (Stardust)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun Mar 5 23:31:49 2006
Message-ID: <200603060430.k264U2529674_at_zagami.jpl.nasa.gov>

http://www.timesonline.co.uk/article/0,,2087-2070393,00.html

Comet dust holds building blocks of life
Jonathan Leake
The Sunday Times (United Kingdom)
March 5, 2006

SCIENTISTS examining the first dust samples collected from a comet have
found complex carbon molecules, supporting the theory that the
ingredients for life on Earth originated in space.

The organic material was found in early studies of samples from the
comet Wild 2 brought back to Earth by the Stardust space probe seven
weeks ago.

Stardust collected hundreds of grains of dust as it flew through the
tail of the comet two years earlier. Analysis suggests a high
concentration of complex molecules of the kind thought necessary for the
evolution of life.

"About 10% of this comet is made of organic materials. We don't know
exactly what they all are but it is very exciting," said Don Brownlee,
professor of astronomy at the University of Washington, who is Nasa's
principal investigator for the Stardust project.

Stardust was launched by Nasa in February 1999 and flew twice around the
sun as it matched its speed to the comet's. Then, in January 2004,
somewhere between the orbits of Mars and Jupiter, it slipped into the
comet's tail of dust and exotic gases, passing within 147 miles of Wild
2's nucleus.

Stardust swept up particles in a collector shaped like a tennis racket
and packed with an absorbent material called aerogel, then spent two
years lining itself up in an orbit that would return it to Earth. On
January 15 it dropped a canister containing the precious comet dust,
which landed by parachute.

Nasa's Johnson space centre carved the aerogel into thin slices, each
containing particles, and sent them out to researchers around the world.
Next week they will share their findings at the Lunar and Planetary
Science conference in Houston, Texas.

The samples will be a treasure trove of organic material, possibly
including amino acids, the building blocks of proteins.

"What we want to know is how organic molecules actually form in comets
and whether they helped deliver organic material to the Earth before
life began," said Brownlee.

The idea that comets delivered the basic components needed for life has
growing support among astronomers. The theory is that the sun and
planets began to form from a vast disc of interstellar dust, gases and
debris about five billion years ago.

The sun would have formed first. Its radiation and gravity would then
have had a powerful influence on the rest of the solar system, driving
lighter molecules of compounds such as water, sulphur dioxide and carbon
dioxide out from the inner solar system.

The process would also have produced billions of comets and meteorites.
Earth was formed 4.6 billion years ago and, as it cooled, these bodies,
some of them huge, bombarded it, bringing organic matter and water. The
first stirrings of life appeared 3.5 billion years ago.

Earth's atmosphere is still showered in dust, meteorites and other
debris every day. This carries water and organic material including
amino acids. But scientists are not sure whether this modern material
has the same composition as the comets and meteorites that hit the young
Earth.

Phil Bland, a Royal Society research fellow at Imperial College, London,
who is working on the Stardust samples, said that comets - deep frozen
for billions of years - were like time capsules. "We can compare what's
in them with what we see now, to work out the processes that have shaped
our planet and all the others," he said.

Monica Grady, professor of planetary and space science at the Open
University, is a member of one of the teams examining the Stardust samples.

"Organic material delivered by comets and meteorites between those dates
[4.6 billion to 3.5 billion years ago] is likely to have played a part
in starting life on Earth," she said.
Received on Sun 05 Mar 2006 11:30:01 PM PST