| Topic: |
Religions > Atheism |
| User: |
"johac" |
| Date: |
19 Dec 2006 01:39:50 AM |
| Object: |
Comets as Toolkits for Jump-Starting Life |
More evidence that the building blocks for life may have come from 'out
there'.
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Comets as Toolkits for Jump-Starting Life
Just as kits of little plastic bricks can be used to make everything
from models of the space shuttle to the statue of liberty, comets are
looking more and more like one of nature's toolkits for creating life.
These chunks of ice and dust wandering our solar system appear to be
filled with organic molecules that are the building blocks of life.
The discovery of two kinds of nitrogen-rich organic molecules in comet
Wild 2 is the latest addition to the set of bits and pieces useful to
the origin of life that has been found in comets.
These discoveries were made by members of the Stardust Preliminary
Examination Team, a group of scientists who have been studying the
samples returned from comet Wild 2 by NASAs Stardust spacecraft in
January 2006.
"These results show that comets could have delivered nitrogen rich
organic compounds to the early Earth where they would have been
available for the origin of life," said Scott Sandford of NASA's Ames
Research Center, Moffett Field, Calif.
"This discovery shows that the menu of compounds available for the
origin of life was richer than had been previously thought," said Jason
Dworkin of NASA's Goddard Space Flight Center, Greenbelt, Md.
"The two molecules we discovered in comet Wild 2, methylamine and
ethylamine, provide a source of fixed nitrogen, a commodity which could
have been rare on the ancient Earth. Nitrogen fixation is the conversion
of the very stable nitrogen (N2) gas in our atmosphere to a biologically
usable form, like an amine or nitrate -- the same compounds found in
fertilizer. Enzymes that fix nitrogen appear to be ancient, so finding a
source of fixed nitrogen would have been an early challenge for life
from the time of its origin. We determined that at least one type of
comet would have provided significant quantities of stable, fixed
nitrogen in the form of methylamine and ethylamine," added Dworkin.
This is the first time these molecules have been detected in comets. As
the Stardust spacecraft sped through the comet's tail at nearly 21,000
kilometers per hour (13,000 miles per hour), a set of aerogel tiles
mounted on a boom trapped dust and gas from the comet. Often referred to
as "frozen smoke", aerogel is the worlds lowest density solid. Its low
density allows it to slow and capture comet dust particles without
vaporizing them.
Although the mission's goal was to return samples of comet dust to
Earth, the researchers looked for organic molecules that were embedded
in the aerogel itself, rather than trapped in dust grains. "We found
that the aerogel acted like a sponge, absorbing organic gases from the
comet nucleus," said Daniel Glavin of NASA Goddard.
"And just like squeezing a sponge, we squeezed out all the good stuff --
the water-soluble organics -- by boiling samples of the aerogel in
ultra-high purity water," added Glavin. The team analyzed the aerogel
water extract with a liquid chromatograph mass spectrometer instrument
to identify the organic molecules.
Since Earth is crawling with life, the team had to rule out
contamination from our planet before it could say the molecules likely
came from the comet. Glavin and Dworkin analyzed dozens of "pre-flight"
aerogels that were not flown on Stardust in order to understand the
organic background levels within the aerogel.
The team found high levels of both methylamine and ethylamine in aerogel
that was exposed to comet Wild 2. While they did find small amounts of
methylamine and trace levels of ethylamine in the pre-flight aerogel,
the total amount in the unflown aerogel was over 100 times less. Also,
the relative amounts of the two molecules were very different from that
found in the comet-exposed aerogel. The different total and relative
amounts convinced the team that most of the two chemicals in the
Stardust sample came from the comet.
However, since Stardust was in space for seven years, the team had to be
sure that the two chemicals weren't simply picked up while the
spacecraft was cruising toward Wild 2. Since the pressure in space is so
low, the spacecraft can release gas or volatile materials acquired
during its manufacture on Earth. This is called "outgassing", and it
could have contaminated the aerogel as well.
To reveal the levels of contamination from these two sources, the
Stardust team included a special piece of aerogel called the "witness
tile" on the spacecraft. It's a piece of aerogel located behind a dust
shield that protected the spacecraft from high-speed collisions with
comet particles. This location kept the witness tile from being exposed
to gas and dust from the comet. But the witness aerogel was exposed to
everything else Stardust encountered, including the manufacturing
processes, shipping, the launch, spacecraft outgassing, and Earth
reentry.
"When we analyzed a sample of the witness tile, we did not detect
methylamine or ethylamine, so we don't think Stardust was contaminated
with these two chemicals on the way to Wild 2," said Glavin.
NASAs Jet Propulsion Laboratory, Pasadena, Calif., manages the Stardust
mission for NASA's Science Mission Directorate, Washington. Dr. Peter
Tsou of JPL is deputy principal investigator and is a co-author on seven
papers about the mission's initial findings appearing in the Dec. 15
issue of Science Express, the online edition of the journal Science.
For more information about Stardust studies and other mission
information, visit:
http://stardust.jpl.nasa.gov/
---
http://www.redorbit.com/news/space/767524/comets_as_toolkits_for_jumpstar
ting_life/index.html?source=r_space#
or
http://tinyurl.com/yaacnc
--
John Hachmann aa #1782
"Those who can make you believe absurdities can make you commit atrocities"
-Voltaire
Contact - Throw a .net over the .com
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