THE news that there could once have been life on Mars may have caught the public imagination, but scientists, ever a cautious lot, are adopting a wait and see attitude in what could yet turn out to be a very controversial debate.

The evidence, they say, is still only circumstantial and was found only in one meteorite. There is always the possibility that the meteorite was contaminated while on Earth, and it will be difficult, if not impossible, to prove that the fossil remains, if that is what they are, really did come from living organisms and not from some other chemical process.

Despite that, scientists contacted by The Irish Times described the news as both "exciting and momentous" and, perhaps more significantly, "not very surprising". For the NASA announcement is just the latest in a string of discoveries over recent years which suggest that life can exist, and indeed may well exist now, elsewhere in the universe.

The controversial British astronomer, Sir Fred Hoyle, who once suggested that life began in deep space and then spread to Earth and elsewhere in comets, may yet be proved right.

Complex organic compounds and amino acids which are essential for life have been found in deep space and in meteorites. On Earth, living organisms are continually being found in extreme conditions where once it was thought life could never survive.

In recent months, astronomers have found evidence for the existence of planets around other stars, while the latest research on Mars suggests that the climate there was once warm and wet and well suited to the development of life, or at least "life as we know it".

Certainly Mars is a possible candidate planet for life: all the necessary chemicals are present, though there is now only a very thin atmosphere, while the extreme cold (the average temperature is about minus 50 degrees Celsius) means that any water present is frozen.

AT least there was water there once, and the Viking missions of 20 years ago returned pictorial evidence of water erosion and striking surface features, including the massive Mariner Valley, which would make our own Grand Canyon look like a drainage ditch.

Many planetary scientists believe that there is still water there, probably buried as permafrost deep under the planet's dusty surface. If life still exists on Mars today, then this is probably where it hides out, safe not just from the searing cold, but also from the intense radiation which bombards the planet.

If the NASA scientists are correct, and life did exist on Mars once, then the big question now must surely be whether life still exists there. While Mars is our nearest planetary neighbour, making space probes and landing missions relatively easy, the 10 month duration of the trip means that sending astronauts there is currently beyond our technological capabilities.

The earlier Viking missions found no evidence of life on Mars, but the experiments carried out then were probably too simplistic. With the latest information, it may be possible to design more sophisticated tests, but probably not in time for the missions already planned for later this year, comprising two from NASA (a Surveyor probe and a landing craft which will analyse soil samples while on the planet's surface) and one from Russia.

Even allowing for the political impetus gained from yesterday's announcement, it will be at least 10 years before a mission can be launched which will be capable of returning from Mars with soil samples for analysis here on Earth.

In the meantime, scientists must make do with analysing those meteorites which are thought to have come from Mars. A number of these have been retrieved from Antarctica over the past 20 years after Japanese geologists realised that meteorites falling there over the millennia, which were subsequently covered and protected by ice, were being released as the glaciers melted. It was from one of these "meteorite fields" that ALH 84001 was retrieved in 1984.

ACCORDING to Dr Ian Eliott, of Dunsink Observatory, meteorites from Mars are rare, partly because they are rocky, not metallic, and thus difficult to spot outside Antarctica. If the NASA findings prove to be true, he says, it means that Mars was once similar to Earth and that the possibility of life elsewhere must be quite strong. "But then I'm not surprised, since I'm sure there's abundant life out there."

Dr Tom Mason, the new director of Armagh Planetarium, who has just returned to Ireland after 20 years studying fossils in Africa, says that the fossil remains which NASA has reported would be very difficult to identify completely and confidently. "You can often find small, round cell like structures that are not organic [biological] at all. The evidence is tricky to confirm."

Dr Patrick Wyse Jackson, curator of TCD's geology museum, says the news is likely to mean that there will be a major rush to study Martian and other meteorites.

But while the scientists debate the possibilities - the scientific research will only be formally published next week - a whole host of social, political and cultural questions arises. If life still exists on Mars, what are our responsibilities, if any? Should we curtail landing missions? If we found living organisms there, should we retreat, attempt to nurture them, or try to colonise the planet with life from Earth?

Four hundred years after Galileo first trained his telescope on Mars, and a century after another Italian astronomer, Schiaparelli, thought he saw canals there, it behoves us to think about these questions.

Yesterday's announcement may not quite have had the Hollywood drama of little green men and close encounters of whatever kind. But one thing seems certain over the coming years there is likely to be more, not less, evidence that there is life elsewhere in the universe.