Microbe Travel Aboard Meteorites Possible
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MICROBE TRAVEL ABOARD METEORITES POSSIBLE, STUDY SAYS
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
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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