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More Martian Microbes?

SKY & TELESCOPE'S NEWS BULLETIN
MARCH 19, 1999

MORE MARTIAN MICROBES?

On Thursday, March 18th, NASA scientists offered new evidence that
fossilized microbes could be present in at least three meteorites from
Mars. Kathie L. Thomas-Keprta (NASA/Johnson) showed that the controversial
stone known as Allan Hills 84001 contains many microscopic crystals of the
iron-rich mineral magnetite. One-fourth of these are perfectly shaped,
same-sized hexagonal prisms free of chemical impurities. Certain bacteria
routinely produce such ultrapure magnetite crystals as a means of orienting
themselves to Earth's magnetic field, and they cannot be formed by any
known inorganic process. Of all the hints of microbial fossils seen in ALH
84001, Thomas-Keprta says the magnetite grains provide the strongest
evidence.

David S. McKay (NASA/Johnson) raised the possibility that two other Martian
meteorites, Nakhla and Shergotty, contain fossilized microbes. His
scanning-electron-microscope views show a variety of round and oval forms
found in tiny cracks within a Nakhla stone. "Are they microfossils?" McKay
asked aloud. "We don't know." But he noted that the blobs are enriched in
iron oxides, a common occurrence when a microbe dies and its cell becomes
mineralized. Moreover, the suspect features are a few tenths of a micron
across, comparable in size to many bacteria. (Many of the putative fossils
in ALH 84001 were much smaller -- too tiny, microbiologists argue, to have
been viable lifeforms.) The NASA team will attempt to examine the blobs'
interiors for hints of cellular structure and to determine whether they
resulted from terrestrial contamination. Unlike ALH 84001, which sat on the
ice fields of Antarctica 16,000 years before its discovery, many pieces of
Nakhla were recovered almost immediately after falling in Egypt on June 28,
1911. McKay's sample came from a fragment with an intact "fusion crust"
that was opened in sterile, clean-room conditions last year.

McKay also showed suspicious features from the interior of Shergotty,
though the study of those is just getting under way. Shergotty crystallized
from molten rock a mere 165 million years ago, whereas Nakhla is about 1.3
billion years old and ALH 84001 is 4 billion years old. Thus, if microbial
fossils really exist in all three of these meteorites, it means that life
has existed on Mars throughout much of the planet's history and could be
there today. NASA hopes to obtain samples of the red planet via spacecraft
as early as 2008, and the agency is currently wrestling with how best to
isolate and study the Martian material once it reaches Earth.

Thomas-Keprta and McKay reported their results at the 30th annual Lunar and
Planetary Science Conference in Houston, Texas, which this year drew nearly
1,100 researchers -- a record attendance -- from around the world.

===========================================================================
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