A geochemist, Jim Papike, who is the Director of the Institute of Meteorites at the University of New Mexico, has recently obtained evidence that the 1996 Mars Meteorite does not contain the isotopic ratios normally seen on Earth when organisms have been present. He and his colleagues examined the pyrite crystals found in the rock fractures, and these samples contain two sulfer isotopes, sulfer-32 and sulfer-34 whose ratio changes on Earth as a result of biological activity. They found that their samples showed no changes that could be expected for processing by Earth-like organisms. Their results will be published in the journal Geochimica et Cosmochimica Acta in August, 1996. This means that the sample was not previously contaminated by Earth microbes. It is possible that martian life forms may not have the same impact on sulfer isotopes as Earth bacteria. But the problem is that if we can continue to explain away negative results as 'just a difference between Earth and Mars life forms' then there is no way to FALSIFY the claim that these are fossil martian organisms. We are, then, not doing science because any theory must be falsifiable.
As of 2000, the general opinion seems to be that the ALH Mars Meteorite probably does not contain the kind of evidence that incontrovertably proves that living systems once existed on Mars. The meteorite, however, was an important catalyst in pushing scientists to their limit to understand just what a fossil life form from another world could look like. After 4 years of very hard work, scientists now have a much better idea of what 'life signs' ought to look like, and how to set up definitive tests for them. This will play an important role once astronauts actually go to Mars and look around first hand.
Meanwhile, a whole new division has been formed at NASA called 'Astrobiology' whose goal is to understand what life 'is', the various forms it can take, and how to remotely look for evidence of it. Mars remains one of the most heavily scrutinized planets, and there are still many ecological niches that Earth 'extremophile' bacteria would find just lovely! Moreover, the satellite of Jupiter, Europa, is considered the second most exciting 'garden spot' in the solar system for extraterrestrial life...but it would be living deep inside the moon within what appears to be a liquid ocean. At one time, Titan was also considered as a candidate, but the more we have learned about its atmosphere and surface, the less likely this seems. Titan is probably pre-biotic, and because of the lack of energy sources to stirr things up, it is a still-born world.
Copyright 1997 Dr. Sten Odenwald
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