Science fiction meets science fact In August, a group of scientists reported the discovery of possible fossil remains of life on Mars -- the first credible evidence that life existed beyond Earth. Granted, the "life" lived fully 3.6 billion years ago, if life it was. The fossil evidence was contained in meteorite that had been collected in Antarctica in 1984 by Roberta Score, on a team sponsored by the National Science Foundation. NSF-funded expeditions have found about 7,000 meteorites in Antarctica. This 4.5 billion-year-old rock may once have been part of Mars. It seems to contain fossil evidence of primitive life on Mars more than 3.6 billion years ago. The rock is preserved at the Johnson Space Center's Meteorite Processing Laboratory in Houston. Courtesy of NASA. Most of these space rocks originated in the asteroid belt, not on other planets, and the meteorite in question lay in storage for about a decade. Then, after David Mittlefehldt, of Dave Mittlefehldt Lockheed-Martin, a contractor at Johnson Space Center, noticed its resemblance to other Martian meteorites, a team lead by David McKay of the Johnson Space Center in Houston studied the remarkable rock. What was the evidence for ancient life? Polycyclic aromatic hydrocarbons (PAHs), organic molecules often associated with life on Earth, were found in fissures in the rock. The PAHs were more concentrated toward the center of the meteorite, which seems to rule out contamination from Earthly organisms. The meteorite contained carbonate molecules (defined), which were also similar to molecules formed by life on Earth. Shapes resembling life were found near these clues. But don't dust off your Jules Verne novels just yet. There are no, repeat, no signs that life still exists on the Red Planet. When the Viking spacecraft visited Mars in 1976, it found no organic molecules on the surface, and telescopes have never spotted those green folks who undoubtedly built the Martian "canals." Magnification of "fossils" in the Martian meteorite. Courtesy of NASA. And even McKay does not argue that the case is closed: "We're not claiming that we have found ... absolute proof of past life on Mars. We're just saying we have found a lot of pointers in that direction." Furthermore, research published in January, 1998, threw cold water on the life-on-Mars hypothesis. Indeed, those pointers were rather minute, according to NASA's press release, and explaining why McKay's team needed to use the latest microscopic and spectroscopic equipment: "The largest of the possible fossils are less than 1/100 the diameter of a human hair, and most are about 1/1000 the diameter of a human hair -- small enough that it would take about a thousand laid end-to-end to span the dot [er, period?] at the end of this sentence." Case closed? Not exactly...

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