Scientists from The Australian National University have found that extensive regions of the sub-surface of Mars could contain water and be at comfortable temperatures for terrestrial - and potentially martian - microbes.

In a new paper, researchers from the ANU Planetary Science Institute modelled Mars to evaluate its potential for harbouring inhabitable water. They found more than they were expecting.

"Our models tell us that if there is water present in the Martian sub-surface then it could be habitable - as an extensive region of the subsurface is at temperatures and pressures comfortable for terrestrial life," said the lead author of the study PhD student Eriita Jones.

Co-author of the paper Dr Charley Lineweaver added: "We know that there is a hot, deep biosphere on Earth that extends to around five kilometres. If there is a hot deep biosphere on Mars, our modelling shows that it could extend to around 30 kilometres".

In an earlier paper, the same scientists modelled the Earth and identified water that was inhabited and water that was not. In this paper, they applied the same technique to Mars and found that a large fraction of the Martian sub-surface could be harbouring habitable water.

"We found that about three per cent of the volume of present-day Mars has the potential to be habitable to terrestrial-like life," said Dr Lineweaver. "This is compared to only about one per cent of the volume of the Earth being inhabited."

"Our conclusion is that the best way to find water - or potentially microbes - on Mars is to dig. Sadly, NASA's Curiosity Rover, which is scheduled to land on Mars in August, has a limited capacity to scratch the surface to 10 or 20 centimetres," he said.

The Planetary Science Institute at ANU is a joint initiative of the Research School of Astronomy and Astrophysics and the Research School of Earth Sciences.

The paper, An Extensive Phase Space for the Potential Martian Biosphere, is published in the Astrobiology Journal. A copy of the paper is available from the ANU Media office.