If life exists anywhere besides on Earth, Mars is the likeliest location, say most planetary scientists. There's just one problem: The Red Planet may never have been warm enough to support the wet biosystems that grace our home planet. But that doesn't mean water didn't flow on the Red Planet. New findings suggest that martian water contained so much salt that it served as antifreeze.
The antifreeze idea comes from an analysis of martian rocks and mineral deposits. A team of scientists from NASA and two Spanish institutions poured over data collected by the rovers Spirit and Opportunity, along with the earlier landers Viking 1 and Pathfinder, at four sites on the martian surface. The results are remarkably consistent. At each of the locations, the same nine elements--silicon, iron, sulfur, magnesium, calcium, chlorine, sodium, potassium, and aluminum--constitute the bulk of the ingredients in the surface rocks. Chemical interactions with all of these elements can keep water from freezing at temperatures well below 0°C, the team reports tomorrow in Nature.
Meanwhile, the team also ran climate models using martian temperature data. Those models show that the planet's atmosphere has always been too thin to support warmer-than-freezing temperatures. Yet satellite photos have shown ravines and features that look a lot like riverbeds and deltas on the martian surface, strongly suggesting that liquid water once flowed there. The only way to reconcile these two pieces of evidence, the team says, is to assume that water on Mars was very salty--as salty as that in the saltiest lakes on Earth--and thus would have resisted freezing. Eventually, as martian temperatures plunged to present-day levels, the water did freeze. In the planet's thin air, it then evaporated, leaving behind the telltale mineral deposits discovered by the four probes.
The paper's analysis is "consistent with the mineral-rich view we're obtaining from the rovers and the orbiters," says planetary scientist James Bell of Cornell University, a member of the Mars rover scientific team. "It's very likely that salty solutions played a role in shaping the martian landscape," agrees planetary scientist Itay Halevy of Harvard University, though he notes there might be other explanations for the mineral deposits.