The sands of Mars, which hold the biggest dunes in the solar system, could contain up to 50 per cent snow and ice, a US scientist told the British Association festival of science meeting in Dublin on Monday (local time).

The discovery could be of enormous significance. President George Bush has named Mars as the destination for a manned mission in the next 30 years.

NASA and the European Space Agency both plan orbiter missions and robot landings in the next decade.

Researchers are also anxious to settle the dispute over whether Mars was ever home to life, and whether microbial life could still endure beneath the soil. Without water, there can be no life.

"This is important because sand dunes occur pretty much everywhere on Mars," said Mary Bourke, of the Planetary Science Institute in Tucson.

"If you are looking for a source of water for future landers, for example, I am advocating that you march up to your nearest sand dune. Perhaps you'll be lucky enough to find a reservoir of very useful volatiles to produce fuels and help the survival of humans on that planet."

She studied satellite images of the planet's north polar sand sea and the southern crater dune fields to identify geological features which could best be explained as dunes that seemed to have been cemented by water.

One of these included the biggest sand dune ever measured: a rigid structure 1,000 metres high. Other landmarks included huge alluvial fans in the sand, river-like drainage patterns, laminated sediments of the kind found on Earth in the dry valleys of Antarctica, and even "cornices" left in the dunes where water had suddenly cascaded away and immediately turned to gas in the thin Martian air.

Some dune slopes were far too steep to be composed of loose dust alone. Other features included "terraces" held in place by some kind of cement long after the loose covering had been blown away by the fierce winds of Mars.

The dunes appeared to be "strong and resistant," rather than the classic type made of shifting sand. "Not many processes can do that," said Dr Bourke. "What I'm suggesting is that water is cementing the sediment."

A series of visits by landers and orbiters since 1996 has confirmed that Mars must once have been wet and warm. The latest research, however, leaves open the possibility that water may have survived below the surface.

Dr Bourke's studies suggest that ancient snow and ice may exist in large quantities only a metre or so below the shifting sands of the fourth rock from the sun.

The findings raise the possibility of a "biological habitat" in the dunes: life would be unlikely to have survived there, but the shifting snows might contain fossil evidence of early Martian life.

Ice has been detected under the soil of Mars at almost every location, but in the greatest quantities at the poles. "The potential amount of snow, and therefore water, is potentially quite high," Dr Bourke said. One huge dune could hold as many as 500 cubic metres of water, she calculated.

Mars periodically changed its tilt dramatically, increasing the severity and violence of its winters. The last time it did so was about 100,000 years ago. "At that time it is reasonable to assume that it snowed at these locations on Mars," she said.

"There's potential, for sure, of finding evidence of life in these sand dunes."

Source: China Daily