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Life after an intriguing Mars fantasy

Ten years later, few experts believe Mars meteorite contains traces of life

— Photo: AP /NASA

An enlarged image of a particle from the ALH84001 meteorite.

NEW YORK: It was science fiction come true: ten years ago, on August 6, 1996, the National Aeronautics and Space Administration (NASA) announced the discovery of life on Mars.

At a Washington news conference, scientists showed magnified pictures of a 1.8-kg Martian meteorite riddled with wormy blobs that looked like bacterial colonies. The researchers explained how they had pried numerous clues from the rock, all supporting their contention that microscopic creatures once occupied its nooks and crannies.

Space buffs and NASA officials said that it just might be the scientific discovery of the century.

Ten years later, the results have not been verified. Sceptics have found non-biological explanations for every piece of evidence that was presented. And though they still defend their claim, the NASA scientists who advanced it now stand alone in their belief.

"We certainly have not convinced the community, and that's been a little bit disappointing," said David McKay, a NASA biochemist and leader of the team that started the scientific episode.

The announcement and the technical paper that followed it practically created exobiology, the scientific field that investigates the potential for life on other planets. And it is undeniable that Mr. McKay and his colleagues have drawn attention to what is a very interesting rock.

The rock in question was discovered in Antarctica. Its name, ALH84001, indicates that it was the first meteorite found during the 1984 research season in the Allan Hills.

At first ALH84001 was misclassified, so it was not until 1993 that researchers even realised the rock came from Mars. But ALH84001 also turned out to be much more ancient than the other known Martian meteorites. At 4.5 billion years old, it dates from a period of Martian history when liquid water probably existed at the now barren planet's surface.

It made sense to ask: Could there be fossils of ancient Martian microbes preserved in the cracks of ALH84001?

The NASA scientists offered four reasons to support their view that the answer is `Yes.'

First, chemical analysis showed that the meteorite contained organic molecules known as polycyclic aromatic hydrocarbons. PAHs can be produced by biological processes. But they are also commonly found in asteroids, comets and meteorites. Sceptics dismissed the importance of PAHs in the Martian meteorite.

A second line of evidence — that the elongated blobs in the electron microscope images could be fossils of ancient Martian bacteria — was also rejected. The problem was, those blobs were much smaller than any bacteria observed on the earth. The two other lines of evidence survived longer. Both revolved around minerals sprinkled through the meteorite that could have been produced by microbes. The first mineral, carbonate, is formed on the earth by remains of living organisms. So finding carbonate in ALH84001 could indicate the presence of ancient microbes in the rock.

The story is similar for magnetite, the other mineral in ALH84001. Some bacteria produce extraordinarily small and pure magnetite crystals.

Some of the most evolutionarily ancient bacteria on the earth produce magnetite, Mr. McKay and his colleagues said. Perhaps ancient Martian microbes did as well; at least some of the magnetite grains in ALH84001 share the shape, small size and remarkable purity of those produced by bacteria on the earth.

For years, Mr. McKay and his detractors argued about how distinctive the magnetite grains in ALH84001 are, and whether a non-biological process could have produced them. Nobody had produced similar magnetite grains in the laboratory. Then somebody did. In 2001, a second team of NASA scientists managed to cook up magnetite grains very similar to the ones in ALH84001. What was more, their laboratory method simulated conditions ALH84001 is known to have experienced during its time on Mars.

Yet David McKay insists the team had not accurately described the synthetic crystals' shape, and that they were not similar to the ones found in ALH84001. He also suggests that the purity of the magnetite crystals stems not from the lab process itself, but from using unrealistically pure raw materials as a starting point. — AP

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