Over a century ago, astronomers looking up at Mars thought it was covered by a network of watery canals, built by an alien civilization. When better telescopes showed this wasn’t the case, a new view of the red planet took hold: one of a barren, freeze-dried desert, completely inhospitable to life. More recently, we’ve learned that, billions of years ago, a young Mars was warmer, wetter, and much more Earthlike than it is today—and now our picture has evolved again. In a stunning announcement, NASA scientists say they’ve found signs of salty liquid water at the surface of present-day Mars. “This discovery suggests it would be possible for there to be life, today, on Mars,” says John Grunsfeld, a former astronaut and NASA’s associate administrator for science.
Evidence comes in the form of long, narrow streaks that descend down valleys and craters, which darken during Martian summertime and fade away when it’s colder. Using an imaging spectrometer on NASA’s Mars Reconnaisance Orbiter, scientists found evidence of hydrated salts, which would significantly lower the freezing point of briny water—like the road salt that’s tossed on frozen roadways during Canadian winters—and allow it to flow. These hydrated minerals, called perchlorates, are necessary to keep liquid water around. “Pure liquid water is highly unstable on Mars,” observes Lujendra Ojha, of the Georgia Institute of Technology, lead author of the paper published in Nature Geoscience, who first observed the streaky formations back in 2010. A glass of tap water on the surface of Mars would freeze or boil away, but some perchlorates can keep liquids from freezing when it’s as chilly as -70° C.
Could such a briny solution support life? Here on Earth, bacteria thrive in all sorts of apparently inhospitable places. They’ve been found living in salty veins of water in the High Arctic permafrost, in Antarctica’s underground lakes, or beneath Chile’s super-dry Atacama desert. We don’t know where the Martian water flows come from, and if they might indicate an aquifer beneath the surface. University of Toronto geologist Barbara Sherwood Lollar has found ancient water buried deep underground at sites in northern Ontario and South Africa, rich in the types of chemical energy that could support microbial life. “If it’s too salty, it can limit life, but if it’s not too salty, it can be advantageous,” she says. “In the deep systems that we look at, the presence of salt is an indicator of extensive water-rock reaction, and we see a lot of energy-rich compounds that can serve as a food source for micro-organisms. In our research,” she says, “salt is a good thing.”
Some scientists believe that if we find microbial life anywhere on Mars, it’ll be under the surface. The European Space Agency’s 2018 ExoMars mission will carry a drill that can get at soil samples two metres deep. NASA’s next Mars rover, scheduled for 2020, which will directly seek signs of ancient life. “Soon, I hope we’ll be sending humans to the red planet to explore,” Grunsfeld says. Not so long ago, the idea of flowing water on Mars seemed fanciful; today, scientists say it’s there. Our planetary neighbour remains full of surprises.