NASA Identifies Carbon-rich Molecules
in Meteors as the 'Origin of Life'
(Top Posts - Science - 092708)

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These molecules, called quinones, are potentially
significant for the "origin of life" or the habitability
of planets. Credit: NASA / Jenny Mottar

Tons, perhaps tens of tons, of carbon molecules
in dust particles and meteorites fall on Earth daily.
Meteorites are especially valuable to astronomers
because they provide relatively big chunks of car-
bon molecules that are easily analyzed in the labor-
atory. In the past few years, researchers have noticed
that most meteorite carbon are molecules called
polycyclic aromatic hydrocarbons (PAHs), which
are very stable compounds and are survivors.

PAHs are the most common carbon-rich compound
in the universe. They are found in everything from
distant galaxies to charbroiled hamburgers and engine
soot. When they are first formed, or found in space,
their structures resemble pieces of chicken wire,
fused six-sided rings. However, when found in mete-
orites, these aromatic rings are carrying extra hydro-
gen or oxygen.

Scientists at NASA Ames Research Center, Moffett
Field, Calif. performed laboratory experiments that
explain the process by which these meteoritic hydro-
carbons attract the extra hydrogen and oxygen. They
are very similar to the molecules identified as evidence
of alien microbes in an earlier Science paper (McKay
et al 1996).

"Our findings are important because it is the first time
anybody explained these carbon-rich molecules found
in meteorites. They are similar to the molecules that
make-up living things," said Max Bernstein, a space
scientist at NASA Ames.


These carbon-rich molecules are produced by carbon-
rich, dying, giant red stars. When they are first formed,
astronomers observe them as normal PAHs. However,
when they are seen in meteorites billions of years later,
they almost always have oxygen or heavy hydrogen
attached to them. (Heavy hydrogen carries an extra
neutron, and is called a deuterium isotope.)

Something happened to change them, say scientists.

To study the process by which these carbon compounds
change, the Ames Astrochemistry Laboratory studied
PAHs in water ices that were exposed to ultraviolet
radiation under space-like conditions. Scientists repro-
duced conditions including an incredibly high vacuum,
extremely low temperatures (- 340 degrees Fahrenheit),
and harsh radiation.

When the extremely cold temperature was reached,
these PAHs were exposed to ultraviolet radiation, and
they changed. The experiment successfully reproduced
the hydrocarbons found in meteorites. For the first
time, scientists were able to show how hydrogen was
exchanged for deuterium, or heavy hydrogen.

"It turns out, you only need water ice and radiation to
change these molecules," said Bernstein.

Using infrared spectroscopy, the Ames research team
proved that the laboratory-produced hydrocarbons
were the same hydrocarbons found in meteorites and
observed through telescopes. Scientists observed the
chemical reaction in a stainless steel chamber as it
was happening. The laboratory sample reflected the
same infrared colors as the hydrocarbons seen by
astronomers using telescopes. Because the techniques
used were the same, the results were directly compar-
able. "We were seeing the same molecules from tele-
scopes as were reproduced in the laboratory," said

Once the molecular-size laboratory sample was re-
trieved, it was taken to Richard Zare's laboratory
at Stanford University, where researchers weighed
the individual molecules. Findings showed that ices,
modified by radiation, created new molecules.

These molecules, called quinones, received consider-
able attention by the astrobiology community because
they are common to all life forms. They are potentially
significant for the "origin of life" or the habitability
of planets. How does a planet become habitable?

"Molecules from space helped to make the Earth the
pleasant place that it is today," said Allamandola,
founder of the Ames Astrochemistry Laboratory.

"Our findings were new because we showed how
these molecules formed. It was already known that
these molecules were in meteorites and delivered
to the planets," said Bernstein.

"We now understand why these life-like carbon
compounds are raining down on the Earth and other
planets. Knowing this will help us search for life on
other worlds by distinguishing these molecules from
biomarkers," said Bernstein.


For further NASA and Ames Astrochemistry Labor-
atory information, please visit:


Ruth Dasso Marlaire
NASA Ames Research Center, Moffett Field, Calif.

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