Original URL: http://www.theregister.co.uk/2011/12/12/martians_lived_underground/

Martians lived underground, say Oz boffins

Water and energy available but not on the surface

By Richard Chirgwin

Posted in Science, 12th December 2011 22:30 GMT

A group of Australian scientists have created a “whole of planet” model that suggests large parts of Mars are capable of supporting life – as long as it doesn’t mind living underground.

Instead of the piecemeal approach followed by most astrobiologists – which, it must be said, is fair enough since the various probes sent to the Red Planet have only sampled tiny areas – the Australian National University team led by Dr Charlie Lineweaver sought to compare what’s known about the whole planet to Earth’s environment.

They focused on two characteristics, comparing the temperature and pressure conditions here to those likely to exist on Mars. Their estimate comes up with a surprise: while only one percent of Earth’s entire volume falls under the heading “habitable”, Mars beats us at three percent.

"What we tried to do, simply, was take almost all of the information we could and put it together and say 'is the big picture consistent with there being life on Mars?'," the astrobiologist told AFP.

Unlike Earth, most of Mars’ habitable zone is underground, Lineweaver says. That’s because water on the surface evaporates due to the low atmospheric pressure (in spite of the rather chilly surface temperatures of around -63 degrees Celsius).

It extends quite a distance underground, in fact: the Martian "pressure-temperature phase space" (that is, the combination of pressure and temperature suitable for liquid water) extends to around 310 kilometers underground, the paper states.

"If there is a hot deep biosphere on Mars, it could extend 7 times deeper than the ~5km depth of the hot deep terrestrial biosphere in the crust inhabited by hypothermophilic chemolithotrophs," the paper continues.

The model found that underground, the extra pressure would allow water to exist as a liquid, and heat from the interior would create conditions "that could be habitable by Earth-like standards by Earth-like microbes".

The paper, An Extensive Phase Space for the Potential Martian Biosphere by Lineweaver, along with Eriita Jones and Johnathan Clarke, is published in Astrobiology. ®