The possibility that vast reservoirs of flowing water exist on Mars will, if confirmed, change forever our perceptions of that planet. As creatures on Earth have peered wondrously into the Universe across the millennia, three spheres within our solar system have always held special significance for mankind: the Sun (for obvious reasons - without it there would be no life on Earth and thus was it worshipped by ancient man); the Moon (regarded with affection, a kindly face watching over us); and Mars, the red planet, threatening and hostile.
Mars was always different. Because of its colour, it was named after the ancient Roman deity of war. As Mars Ultor, the God (a male deity, of course) was the personal guardian of the Emperor, the avenger against anyone who dared take up arms against Caesar. Modern science fiction built on ancient perceptions: Mars was the place from whence would come the Martians, the not so friendly little green men intent on conquering Planet Earth. At the end of the nineteenth century, there was furious debate among astronomers over what were thought to be canals which were, according to some, bands of vegetation, fed by irrigation ditches built by intelligent beings. But since Mariner 4 captured the first spacecraft images of Mars in 1964, our understanding has been rooted less in mythology and imaginative speculation, and more in scientific reality. Which is not to say that excitement is thereby diminished.
Yesterday's announcement by America's National Aeronautics and Space Administration that evidence exists to suggests the planet may contain water which flows occasionally on the surface will quicken the pulse of those captivated by the possibility that we are not alone in the Universe. Without water, there can be no life. But with water, specifically flowing water, there exists at least the possibility of life. It is this possibility which now fires the imagination. Since March last year, the Mars Global Surveyor satellite orbiting the planet has transmitted thousands of detailed and very clear pictures to Nasa.
What scientists believe they have seen are entrenched, steep-sided V-shaped valleys, fanning out into delta-like shapes. In other words gullies, soil and rock deposits that correspond to topography on Earth sculpted by one thing only: moving water. For some years, scientists have suspected that Mars contained water but only in a frozen form in polar regions. As a Nasa scientist said yesterday, the possibility of flowing water a few metres below the surface has profound implications: accessible water on a neighbouring planet has been the holy grain of space exploration. It raises the possibility not just of life in the past and, perhaps, in some shape or form in the present - but also of colonisation in the future. Where there is water, there is hydrogen and oxygen and with both comes the possibility of creating breathable air, rocket fuel and growing plants for food.
Nasa is due to launch two further missions to Mars: one next year, another in 2003. With the latest discovery providing a glimpse of exciting new vistas, the pressure will be on to learn ever more. As one Nasa scientist put it yesterday: "This is one heck of an interesting planet. . . "