A new study says that large regions of Mars’ subsurface could be even more sustainable for life than previously thought. Scientists found that large regions could be capable of sustaining life -- three percent of the planet actually, albeit mostly underground. It is already known that there are vast deposits of ice below the surface, so there could be liquid water a bit deeper where it is warmer. Those conditions would be ideal for bacteria or other simple organisms.
Modified from http://www.universetoday.com/91848/new- ... tain-life/.