Stanford Today Edition: March/April, 1998 Section: Science and Medicine: No Martian Life After All? WWW: No Martian Life After All?
Science and Medicine News
New analyses of the famous Martian meteorite, ALH84001, have cast doubt on the likelihood that it contains the fossilized remains of ancient Martian microbes.
Two studies published in January find that much of the organic material in the meteorite appears to be terrestrial, rather than extraterrestrial, in origin.
Richard Zare, the Marguerite Blake Wilbur Professor of Chemistry at Stanford, who headed the team that discovered organic material of possible Martian origin in the meteorite, says that the new findings do not directly refute the original research. One of the analyses, however, suggests that the meteorite contains more terrestrial contamination than he had originally thought.
ALH84001 was thrust into the limelight in August 1996 when a team of scientists published a controversial analysis in the journal Science, arguing that they had discovered organic material, unusual mineralogical features and electron microscope images showing tiny oval and worm-shaped features that provided compelling circumstantial evidence that the meteorite had been inhabited by Martian microorganisms more than three billion years ago.
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.
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. ST