The Martians of summer are facing a hard winter. Their very survival is in question.
New research has cast a cold shadow over the sensational claims made in August that a meteorite that fell on Antarctica carried chemical and possibly fossil evidence of primitive life on early Mars -- microbial Martians.
The possibility revived speculation about life on other worlds, an idea ever latent in science and the human imagination, and seemed to provide additional impetus for projects to explore the neighboring planet, including two American spacecraft now on their way.
But independent tests conducted since the meteorite announcement have shown that the supposed evidence for Martian life can be explained in nonbiological terms, scientists said.
What had been detected in the potato-shaped rock could well be neither animal nor vegetable, but strictly mineral.
The results of one study, researchers concluded, invalidated three of the four lines of evidence offered in support of the claim that the meteorite contained traces of microorganisms on Mars from long ago, when the planet was a warmer, wetter place.
It is unclear, they said, whether the fourth clue -- the presence of the kind of organic molecules that are common on Earth and are often related to biological activity -- can stand alone as evidence of past life.
But another study raised suspicions about that, too. It suggested how contaminants from the Antarctic ice could have misled scientists into thinking they had found the first sign of Martian organic molecules.
John Kerridge, a planetary scientist at the University of California at San Diego who is familiar with both studies, said, "The biological explanation for the meteorite is becoming less and less plausible."
The scientists raising the doubts spoke in apologetic tones about the implications of their research.
One of them, Dr. Harry McSween Jr. of the University of Tennessee at Knoxville, said, "It makes me feel like the Grinch stealing everybody's Martians."
McSween and others said their findings did not rule out microbial Martians. They emphasized that while the meteorite clues might be suspect, other intriguing circumstantial evidence remained that suggests that some forms of rudimentary life could have existed on Mars 3 billion to 4 billion years ago and could still exist today in moist soil beneath the surface.
Earlier spacecraft revealed topography indicating that water must have once covered parts of the planet and could have created conditions favoring the emergence of life.
So far, the scientists who first saw in the meteorite "fossil remains of a past Martian biota," as they reported then in the journal Science, are not yielding an inch. They are studying the new research, they said, but could see no reason yet to revise or withdraw their interpretation.
Responding to the critics, David McKay of the Johnson Space Center in Houston, a leader of the initial meteorite study, said: "We disagree with their interpretation, and we're basically not worried by all this. For one reason, we don't think they're looking at the same places in the meteorite."
McKay said that his group of scientists from the National Aeronautics and Space Administration and several universities would be reporting in two or three months its own new findings based on further examination of samples from the rock.
One challenge for them has been to develop microscopic techniques so fine that they could detect any preserved cell walls in the supposed microbe fossils, if these are indeed fossils.
Only by finding such tiny cell walls, biologists had said, were the meteorite scientists likely to dispel skepticism toward claims of detecting evidence of Martian life. But McKay declined to discuss the group's latest results.
Pub Date: 12/22/96