Overview of our article to appear in the Feb 19 issue of Science.
MOUNTAIN VIEW, Calif. -- By simulating the conditions in clouds of dust between the stars, scientists from the NASA Ames Research Center and Stanford University have shown that chemicals essential for life are formed in the depths of space. These findings may shed light on how life may have arisen.
NASA Scientists Max Bernstein, Scott A. Sandford, and Louis J. Allamandola created biologically important molecules in lab experiments designed to simulate the chemistry of the interstellar medium. These molecules were analyzed by Stanford University Professor Richard Zare, graduate student J. Seb Gillette, and Dr. Simon Clemett.
The results are reported in the Feb. 19 issue of the journal Science.
The new research confirms scientist's suspicions that dark clouds of dust play a central role in the production of organic chemicals that served as the building blocks for the development of life on Earth. The dust of which these clouds are composed plays an important role in the life cycles of solar systems. It is the debris of previous generations of stars and the stuff from which, in time, new stars and solar systems will come.
By analyzing the light that passes through them scientists have determined that these dark clouds are comprised of tiny sand-like grains each covered by a thin layer of ice. The temperatures in these dark clouds are so cold that air would freeze solid. The average temperature is 10 K (about -440 F; -260 C) and a whole dust grain is perhaps one ten thousandth of a millimeter across. The ice is composed primarily of water but often contains some organic molecules. Despite the frigid conditions, the dust particles are bathed in ultraviolet (UV) radiation that provides the energy to drive chemical reactions.
Previously, Dr. Louis Allamandola of NASA-Ames shown that a family of carbon-containing compounds, called polycyclic aromatic hydrocarbons (PAHs), which are common on Earth in coal, soot, and automobile exhaust, are the most abundant class of organic molecules in the Universe. PAHs are flat molecules of carbon and hydrogen in the form of hexagons so that their skeleton looks like chicken wire. Drs. Bernstein, Sandford, and Allamandola took PAHs, froze them into ice under conditions like those in dark clouds, exposed them to UV radiation, and sent the stuff they made to Professor Richard Zare at Stanford University.
"We wanted to see what chemistry could occur under conditions like that in dark clouds, the places where solar systems are made," said Max Bernstein, a chemist at NASA Ames through a cooperative agreement with the SETI Institute. "We made a bunch of oxidized PAHs including aromatic ketones, alcohols, and ethers. These kinds of molecules are in cosmetics and medicine that will be familiar to many. For example, they are found in aloe, henna, and St. John's Wort." he explained.
"The same kinds of compounds that we detect in our experiments have been found in carbon rich meteorites," said Scott Sandford, a NASA civil servant who recently returned from collecting meteorites in Antarctica. "We are now seeing how these molecules in meteorites may have formed" said Sandford. "When these experiments are performed in ice made from deuterated (heavy) water the deuterium is incorporated onto the PAHs. This may explain why the PAHs seen in meteorites carry so much deuterium," he added.
"These oxidized PAHs are made in the interstellar medium and brought to Earth in interplanetary dust particles (microscopic bits of comets and asteroids) that drift down to Earth by the ton every day," said Dr. Allamandola, the senior group member. "These compounds we have made, and Dr. Zare's group has analyzed, are similar to those ubiquitous in living systems today, and play important roles in essential biological processes. For example, quinones (oxidized PAHs) play a crucial part in electron transport in cells." Dr. Allamandola points out. "Perhaps such molecules were exploited by the Earth's earliest organisms and that is how these kinds of compounds become incorporated into our biochemistry. This is dead center of the Astrobiology bulls-eye," he added, in a reference to the recent importance that NASA has placed on this subject.
"It means," Zare said, "that if conditions in the interstellar medium favor the formation of possible organic building blocks of life, then it would seem that the odds go up of finding carbon-based life elsewhere in the Universe."
This work, like most science, was the result of cooperation. The lab experiments were performed at the Astrochemistry Lab at NASA Ames by Drs. Max Bernstein, Scott Sandford and Louis Allamandola, but the mass spectral analysis was carried out at the Chemistry Department at Stanford University by J. Seb Gillette, Dr. Simon Clemett and Professor Richard Zare. You can learn more about NASA Ames Astrochemistry Lab by visiting
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