SCIENTISTS are on the threshold of the most exciting discovery about humanity’s place in the Universe since Galileo and Copernicus proved that the Earth goes round the Sun.

The European Mars Express spacecraft has determined beyond reasonable doubt that water, the prerequisite for all forms of terrestrial life, still exists on the Red Planet, and that it once flowed in torrents across its surface.

These remarkable revelations about our celestial neighbour provide the most tantalising evidence yet that the miracle of life on Earth may not be unique, even within the confines of the solar system.

Wherever water is found on the Blue Planet — from the tundra of Antarctica to the depths of the ocean floor — we know there is life. For life as we know it, we need water. Now we can be certain that this vital commodity is present, and may once have been abundant, on the surface of Mars.

It seems more probable than ever that the planet, so long considered barren and inert, may once have supported life.

It would be no exaggeration to compare such a discovery to the Copernican revolution, which put paid to the notion that the Earth stood at the centre of the Universe, or the voyages of Columbus and Magellan, proving the world to be round. It would mean that life has arisen twice on planets separated by as little as 35 million miles. And if that is so, it is probably common throughout the Universe.

We are not quite there yet. Neither Mars Express, nor Nasa’s Spirit and Opportunity rovers, are designed to test the soil and rock for the chemical evidence that would provide definitive proof. Indeed, the European probe’s results make it more frustrating than ever that Beagle 2, the British lander that was sent to Mars specifically to search for life, remains incommunicado.

The evidence of water, in the form of ice, makes it yet more important that we refuse to give up and dispatch Beagles 3, 4 and 5 to the Red Planet to resume the search.

We should not hold our breath for intelligent Martian life. Anything we find there will be extremely primitive, hardy microorganisms that can cope with extreme cold and harmful ultraviolet rays. These can live under the most unlikely of conditions: the Apollo moon landings turned up microorganisms carried years before as passengers on an unmanned probe.

Martian life could be found in the form of fossils that died out long ago. Or it could survive in certain suitable zones. The search will be a little like opening a window on the Earth billions of years ago.

There are times when science is more like hearing a Beethoven quartet than poring over reams of numbers. Yesterday was one of those occasions.

To look at the pictures from Mars Express’s high-resolution stereo camera was to see something so supremely beautiful that I had to remind myself it was science, not art. These images would not have looked out of place at the Royal Academy’s Summer Exhibition.

Yet they tell us so much. There can be little doubt that the vast channel of Reull Vallis was carved by flowing water. It has water deposition and erosion: there is no way it could be anything else. When we look at Valles Marineris, it is as if we are gazing on the canyons and mesas that are so familiar to us from the American South West. It is a landscape of desolation and grandeur, but one that might possibly have harboured life.

This voyage of discovery encompasses so many great aspects of human endeavour. Important scientific advances are being made. But it is also advancing the achievement of the human race.

• Dr John Murray, a research lecturer at the Open University, was speaking to Mark Henderson, The Times’s Science Correspondent

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