By PAUL RECER
AP Science Writer
TUCSON, Ariz. (AP) -- In their first appearance before a major audience of professional astronomers, NASA scientists vigorously defended their theory that a meteorite from Mars shows evidence of ancient life on the red planet.
Though they got respectful applause from researchers at a meeting of the planetary division of the American Astronomical Society, the team from the National Aeronautics and Space Administration also got blunt skepticism and an outline of what they must prove to satisfy critics.
"This is not bad for a new theory. It is much better than cold fusion," said Timothy Swindle of the University of Arizona, referring to a widely advertised atomic energy theory that was denounced within days. "Nobody has found such obvious flaws in this work."
But he said that few astronomers are ready yet to accept the Mars life theory.
David McKay and Everett Gibson of the Johnson Space Center, leaders of NASA's Martian meteorite team, said they have received calls, letters and electronic mail criticizing their theory, but are unshaken.
"We haven't seen anything to cause us to change our initial interpretation," McKay said.
The NASA team announced in August that in a meteorite thought to have come from Mars they found microscopic and chemical evidence of minute forms of life that they believed lived in the rock when it was on the Martian surface. The rock was believed to have been jolted away from Mars by a massive impact 16 million years ago, landed in the Antarctic 13,000 years ago and was found in 1984.
An analysis of the meteorite uncovered traces of chemical compounds known to be formed on Earth by bacteria. The researchers also found what they said were fossilized remains of nanno-bacteria, microbes so small they could be seen only with powerful electron microscopes.
Some biologists have rejected the fossil claim, saying no nanno-bacteria of that tiny size have been identified.
But McKay said Wednesday that, with the help of microbiologists, he has uncovered samples of Earth bacteria that closely resemble the shapes found in the Mars specimen. He said such bacteria have been found in rocks drilled from deep beneath the Columbia River basin and from natural varnish found on ancient rocks.
He showed pictures of both Earth and Mars samples with spherical shapes that closely resembled each other.
"Our interpretations are consistent with what is seen in terrestrial samples," McKay said.
The NASA team is developing a technique to dissect the minute fossils to see if they can detect cell membranes, an undeniable mark of life, he said.
A number of astronomers in the audience asked pointed questions and several times McKay and Gibson admitted they had yet to develop enough evidence to settle some controversial issues.
Swindle, speaking for the association as the "resident critic," said an informal survey found only faint support among the gathered experts for the NASA theory.
"Of the 20 or 30 people I have talked to, the typical response is that there is between a 10 to 50 percent chance of this being right," said Swindle. "I am not convinced by the evidence that they are right or that they are wrong. We simply don't know."
Swindle said the NASA theory would be helped if other researchers show that some of the complex chemical compounds in the Mars sample can be formed at temperatures consistent with life. He said proof of nanno-bacteria fossils existing on Earth and proof of cells walls in the Mars specimens also would boost the NASA case.
On the other hand, he said the NASA theory would be weakened if other researchers find that the microfossil shapes could be formed in natural minerals, if others fail to find microfossils in Mars samples now being studied, or if microfossil shapes like those in the Mars sample are found in meteorites that did not come from Mars.
At the end of the session, Gibson said he felt their research stood up under the grilling.
"I'm pleased," he said. "We've done well."
McKay said that whatever is decided, the work has ignited new interest in the search for extraterrestrial life.
"Even if we are wrong," he said, "we have stimulated a lot of new study by microbiologists on the evolution of life."
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