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Microbe Travel Aboard Meteorites Possible

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    NHNE News List Current Members: 387 Subscribe/unsubscribe/archive info at the bottom of this message. ... MICROBE TRAVEL ABOARD METEORITES POSSIBLE, STUDY SAYS
    Message 1 of 1 , Oct 29, 2000
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      By Usha Lee McFarling
      Los Angeles Times Science Writer
      Friday, October 27, 2000


      For two centuries, scientists have suspected that life might be able to
      travel between planets via meteorites, and even suggested that life on Earth
      may have originated elsewhere in the solar system.

      But there's been one problem. All meteorites are generated by explosive
      impacts on their home planets. Could any living organism survive the massive
      shock and heat of such a blast?

      Now, a team led by three Caltech scientists says that any contents in the
      rocks could indeed survive. Conducting an extremely precise magnetic
      analysis of a Martian meteorite, the group found that the core of the
      meteorite did not reach more than 104 degrees Fahrenheit--far below the
      sterilization temperature of 230 degrees.

      "Thirty years ago, it was thought a rock could not be ejected from a planet
      without melting or vaporizing it," said Benjamin Weiss, a Caltech graduate
      student and lead author of the research published in today's issue of
      Science. "This is the first evidence a rock was blasted off Mars and got to
      Earth without being heated beyond 104 degrees, and perhaps not even above
      room temperature."

      Weiss' team studied a controversial meteorite known as ALH84001, a 4
      1/2-billion-year-old rock from Mars that has been extensively studied and
      vigorously debated since 1996 because it appeared to contain microfossils
      created by extraterrestrial life.

      The issue has not been resolved, and many scientists remain skeptical of the
      assertion. The new study did not address the question of whether the
      meteorite had ever contained life, but answered a broader question of
      whether life could theoretically be transferred between planets.

      "There's every reason to think life can go back and forth," said Joseph
      Kirschvink, a professor of geobiology at Caltech and coauthor of the paper.

      In the 1980s, H. Jay Melosh, a professor of planetary sciences at the
      University of Arizona in Tucson, was the first to suggest that meteorites
      might be able to evade heat sterilization. Rocks near the surface, he
      surmised, could be ejected from a planet with very little shock damage.
      Though this might occur in only 2% of ejected material, it held open the
      possibility that life on those surface rocks could survive the blast as

      Until now, Melosh never had any proof his theory was correct.

      After the ejection blast, microbes atop a meteorite traveling through space
      would still face a deadly barrage of cosmic rays. Those within the meteorite
      could be killed off by the rock's own radiation.

      Entry into Earth's atmosphere does not turn out to be so hazardous. The
      passage generally takes less than 20 seconds. While heat might cause the
      surface of the rock to boil off, that heat wouldn't penetrate too deeply.
      When meteorites land on earth, they are generally covered with frost.

      "People have gotten frostbite picking them up," said Kirschvink.

      To test how hot the rock had been, the scientists analyzed the magnetism in
      a small chip. A meteorite heated to high temperatures would lose its
      original magnetism and instead reflect the magnetism present where it

      They found that the outer surface of the meteorite was aligned with the
      Earth's magnetic field. The interior, however, retained a randomly oriented
      magnetism. When the researchers heated a slice of the meteorite, it started
      to demagnetize at 104 degrees--showing the interior had never reached that

      The subtle measurements were possible due to a machine developed by study
      coauthor Franz J. Baudenbacher at Vanderbilt University in Nashville. The
      machine, an "ultrahigh resolution scanning superconducting quantum
      interference device microscope," detects microscopic changes in magnetism,
      said Kirschvink, and is 10,000 times more sensitive than similar machines.

      Other questions center on just how long microbes could stay alive in space.
      Bacteria on a satellite have survived the vacuum of space for more than five
      years. Some bacteria on Earth have shown a remarkable ability to survive
      desiccation and radiation, both in nature and the laboratory. "We do all
      sorts of things to insult them, and they do just fine," said Melosh.


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