LIFE ON MARS

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Cornell University astronomer Carl Sagan, perhaps the most prominent champion of the search for extraterrestrial life, was exultant. "If the results are verified," he said, "it is a turning point in human history, suggesting that life exists not just on two planets in one paltry solar system but throughout this magnificent universe."

At the Washington press conference, hastily convened after word of the discovery leaked to the journal Space News, NASA Administrator Daniel Goldin echoed the excitement. "It's an unbelievable day," he said. "It took my breath away." But, he cautioned, "the scientists are not here to say they've found ultimate proof...We must investigate, evaluate and validate this discovery, and it is certain to create lively scientific controversy."

Members of the NASA-led team arrived in Washington fully prepared to enter the fray. They distributed copies of their peer-reviewed report, which the prestigious journal Science accepted for publication in this week's issue, and displayed some remarkable scanning electron-microscope images of the tiny structures found inside the meteorite.

The most striking image clearly showed a segmented, tubelike object, with a width about a hundredth that of a human hair, and to the untrained eye clearly resembling a life-form. Apparently to some trained eyes also. "When I took it home and put it on the kitchen table," says Everett Gibson Jr., a geochemist at the Johnson Space Center, "my wife, who is a biologist, asked, 'What are these bacteria?'"

Among other images, one revealed carbonate globules--circular features closely associated with fossils of ancient bacteria on Earth. Another showed what seemed to be colonies of sluglike creatures.

As startling as these images were, they constituted just one of several lines of evidence that team leader David McKay cites as "pointing toward biologic activity in early Mars." In addition to the images, which McKay acknowledges are the weakest and most controversial parts of the evidence, the panel of scientists at the press conference cited complex chemicals found close by or inside the carbonate globules. These included polycyclic aromatic hydrocarbons (PAHS)--organic molecules that on Earth are formed when microorganisms die and decompose (but also when certain fossil fuels are burned)--and iron sulfides and magnetite, minerals that are often (but not necessarily) produced by living organisms.

That raised an obvious question. Could these compounds have resulted from earthly contamination of the meteorite during its long Antarctic layover? Not likely, says Richard Zare, a Stanford University chemist who developed and used the analyzer that detected the PAHS and other meteoric hydrocarbons. The researchers performed a "depth profile" on the meteorite, and although no pahs were found on its crust, they were found inside the rock. Had any of Earth's abundant PAHS seeped in, says Zare, he would have expected to find more contamination on the outside than in the interior.

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