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Life on Mars
In the 17 months since the research was announced, other scientists
have published dozens of independent analyses that have both supported
and attacked the Martian microbe hypothesis. In the last month, however,
the weight of new research appears to be stacking up against the
pro-Martian position.
In December, John Bradley of MVA Inc. and Ralph Harvey of Case
Western Reserve University published a paper in the journal Nature
that attacked the NASA group’s interpretation that the oval and
worm-like shapes that it reported could be the fossils of
microorganisms. Duplicating the NASA researchers’ methods, Bradley and
Harvey reported that the shapes they could find in the meteorite are
non-biological in nature and consist of fractured surfaces of common
crystals.
In another study, a team from the University of Arizona, headed by
A.J. Timothy Jull, burned samples of the meteorite at two different
temperatures to separate the organic carbon from the carbon contained in
inorganic minerals. They then analyzed the isotopic ratios of the carbon
from the two sources and found that four-fifths of the material had the
same isotopic signature as terrestrial carbon. The other 20 percent
appears to have a preterrestrial origin, they found.
Zare’s interpretation is that there is “a much greater degree of
terrestrial contamination in the meteorite than I suspected was present
two years ago,” but that it doesn’t completely rule out an
extraterrestrial origin. “Jull’s work is for the whole rock. As in real
estate, location is everything. His study does not give any indication
of the locations from which these different carbon isotope fractions are
coming.”
The saga of the provocative rock is far from over. Last summer NASA
and the National Science Foundation awarded grants for 23 new
investigations of ALH84001 as part of a coordinated program designed to
determine whether it contains traces of alien life.
Although it may be decades before the significance of the meteorite
is determined, Zare sees several beneficial effects that are independent
of the debate: a revitalization of research on meteorites and major new
impetus to research related with questions like “How did life begin on
Earth?” and “Is there life beyond Earth?” among others.
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