14 DAY TRIAL // As soon as it arrived on the surface of the Red Planet, the Mars Exploration Rover Opportunity investigating the south equatorial regions discovered evidence of the past existence of liquid water, fueling even further the idea that Mars was once able to support life. However, a new assessment of the conditions required for the appearance of life on a particular planet shows that liquid water alone is not enough to support life.
"Liquid water is required by all species on Earth and we've assumed that water is the very least that would be necessary for life on Mars. However, to really assess Mars' habitability we need to consider the properties of its water. Not all of Earth's waters are able to support life, and the limits of terrestrial life are sharply defined by water's temperature, acidity and salinity," said postdoctoral researcher Nicholas J. Tosca from Harvard University.
Analysis of Martian rocks shows that the liquid water flowing across them would have been rather salty.
"Our sense has been that while Mars is a lousy environment for supporting life today, long ago it might have more closely resembled Earth. But this result suggests quite strongly that even as long as four billion years ago, the surface of Mars would have been challenging for life. No matter how far back we peer into Mars' history, we may never see a point at which the planet really looked like Earth," said Tosca's colleague and participant in the study, Andrew H. Knoll.
On Earth, only a few organisms are able to sustain high levels of salinity, amongst which Halophiles, that could have originally evolved from organisms living in pure waters, meaning that it is highly unlikely that life would emerge from salty waters.
"Nevertheless, this doesn't rule out life forms of a type we've never encountered, but life that could originate and persist in such a salty setting would require biochemistry distinct from any known among even the most robust Halophiles on Earth," said Knoll. And since the only rocks that where analyzed came from the regions of the planet investigated by Opportunity, the study still leaves hope that less salty waters may have flowed in other regions of the planet.