April 26, 2001
Vol. 20 No. 15

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    Argonne Lab experiment simulates comet collision

    Hitchhiking molecules could have survived fiery comet collisions with Earth, according to a major new experiment done by researchers at Argonne National Laboratory, the University of California, Berkeley, and Lawrence Berkeley National Laboratory.

    A report of the results was presented at the annual meeting of the American Chemical Society in San Diego and published in the February issue of the international scientific publication Origins of Life and Evolution of the Biosphere.

    The experiments simulated a high-velocity comet collision with Earth. The results give credence to a theory that the raw materials for life came from space and were assembled on Earth into the ancestors of proteins and DNA.

    Randy Winans and Mike Ahrens of Argonne’s chemistry division were members of the research team performing the experiments. The researchers shot a soda-can-sized bullet into a nickel-sized metal target containing a teardrop of water mixed with amino acids, the building blocks of proteins. More than 70 varieties of amino acids have been found in meteorites and are presumed to exist in interstellar dust clouds. These amino acids are suspected to make up the cores of comets that smashed to Earth during its early history.

    “Comets are all frozen, so amino acids could be preserved within them,” Winans said. “Assuming that the comets did not directly hit the Earth, but glanced the surface, they could have survived the fall.”

    Not only did a large fraction of the amino acids survive the simulated comet collision, but also many polymerized into chains of two, three and four amino acids, so-called peptides. Peptides with longer chains are called polypeptides, while even longer ones are called proteins.

    The ballistic test was designed to simulate the type of impact that would have been frequent some four billion years ago, when rocky, icy debris in our solar system accreted to form the planets in what must have been spectacular collisions. Much of the debris would have resembled comets that slammed into Earth at velocities greater than 16 miles per second.

    The severity of the laboratory impact was akin to an oblique collision with the rocky surface of the Earth–a comet coming in at an angle of less than 25 degrees from the horizon, rather than head-on perpendicular to the Earth’s surface.

    After the simulation, Winans and Ahrens analyzed the results using liquid chromatography and mass spectroscopy to determine the species and concentrations of molecules present.

    The experimental results suggested that some water ice from the comet would remain intact as a liquid puddle concentrated with organic molecules, ideal for the development of life. This impact scenario provides the three ingredients believed necessary for life: liquid water, organic material and energy.

    The National Science Foundation, NASA and the U.S. Department of Energy sponsored the work.

    The University operates Argonne National Laboratory for the U.S. Department of Energy.