LIFE ON MARS?

Later, unmanned Russian and American space probes and orbiters began broadcasting information back to Earth that seemed to end hopes that even primitive life forms, such as algae or funguses, might exist on the planet. Mariner 4, which flew past Mars in 1965, led scientists to conclude that the planet possessed neither an atmosphere and nor water, both prerequisites for life as we know it. A decade later, the Americans landed their Viking spacecraft, which managed to scoop up some soil samples for testing. Nothing was found to suggest that there was life on Mars, or ever had been.

Now, it seems that such conclusions may have been premature. Scientists in the United States have drawn some rather startling conclusions about the possibility of ancient forms of life on Mars from a meteorite, rather prosaically named ALH84001. About the size of a mango, it was discovered by American scientists a dozen years ago in Antarctica. (Actually, Japanese researchers had first found the meteorite zone.) The scientists now believe the rock was shaken loose from Mars during another meteor collision about 16 million years ago and eventually crashed down on Earth.

The meteorite itself is thought to be some 4.5 billion years old, which would place it at the very beginning of the formation of the solar system and of life on our planet. Inside its core are infinitesimal tube-shaped objects. These, argue the American researchers in the respected Science magazine, may be micro-fossils of ancient Martian life forms. The scientists also cite the presence of chemical compounds normally associated with biological activity. Of course, the "fossils" may also be nothing more than dried mud. But the alternative prospect is tantalizing. It would provide powerful indications that life may have begun its evolutionary journey on another planet besides ours.

Humankind has moved a long way from the belief that the Earth, and its inhabitants, were at the center of the universe or were unique. Indeed, evidence to the contrary accumulates daily. In the past two years, the supposition that other stars have their own planetary systems has been empirically confirmed. More and more educated people are now receptive to the notion that there are other forms of life in the universe. Opinion polls show that a great many Earthlings believe their planet has been visited by alien beings.

No responsible scientist suggests that there are little green men on the red planet. But the question of whether primitive life once existed there -- and why it might have died out -- certainly has become more intriguing. Already, the latest findings have raised anew the issue of sending out more scientific probes or even a manned mission to Mars. New evidence and changing attitudes mean there is much greater reason now to launch them than before. No matter how much research is done on Martian meteorites on Earth, there will not be wide acceptance of the findings until somebody manages to go to Mars and bring back more samples for study.

Many mysteries still surround the question of life on Mars, waiting to be explored. The Mariner 9 and Viking orbiters sent back detailed photographs of sinuous channels that resemble dry river beds. They strongly suggest that while flowing water may not be present now, Mars almost certainly had abundant supplies in the past. There is the continuing puzzle over the planet's polar caps, which expand and shrink with the changing seasons. Are they made of water ice or carbon dioxide? What appear to be ancient lake beds are ripe for investigation, perhaps through deep-bore probes. Some scientists think that the Martian surface has been sterilized of life forms by heavy cosmic radiation.

Seven years ago, U.S. President George Bush proposed a manned mission, though the $400-billion price tag quickly dampened enthusiasm. But his blueprint, involving complex orbiting space stations, may have been gold-plated by design. Other proposals put the costs of a pared-down mission at just $50 billion. Indeed, any manned flight would almost certainly be an international effort, possibly linking the U.S. and Japan, which is planning an unmanned Martian probe of its own. That would be an inspiring start to a new century of exploration.