Our own astrobiologist Charley Lineweaver (my supervisor) and his PhD student Eriita Jones have just published a paper showing that about three per cent of the volume of present-day Mars has the potential to be habitable to Earth-like life.
While the evidence for wet Mars in the past has been building up (Gypsum found recently), the average surface temperature on Mars today is minus 63 degrees Celsius and so you might think any water present now will be in the form of ice. This is true to some extent as we found out last year when the Pheonix mission which actually touched frozen water that is found at the poles on Mars. What about any ice that melts? Couldn’t that become a liquid capable of sustaining life?
Turns out that the low-pressure environment of Mars means water cannot exist as a liquid and will vaporise on the surface (similar to dry ice or solid CO2 sublimating on Earth’s surface). But the authors of this study have found that the conditions are right underground, where the weight of the soil gives the added pressure required to keep the water in a liquid state. It would also be warm enough, for bacteria and other micro-organisms to thrive due to heat from the planet’s core.
This study undertaken at the Planetary Science Institute at ANU examined how much of the planet could sustain water that could be habitable by Earth-like standards by Earth-like microbes. The modelling shows that it could extend to around 30 kilometres depth (compared to Earth’s just 5 kilometres) – which means there could be more life on Mars than on Earth!
While it is unlikely that the Curiosity Rover which is due to land on Mars in August 2012 will be able to dig deep enough to sample the liquid water, I have a feeling that within the next decade or so we will send a drilling rig to Mars and fish out those little critters swimming in the subsurface aquifers of Mars 😉
More info here