Nasa scientists find evidence of flowing water on Mars
Researchers say discovery of stains from summertime flows down cliffs and crater walls increases chance of finding life on red planet
For years, scientists have known that Mars has ice locked away within its rusty exterior. More elusive, though, is figuring out how much of that water is actually sloshing around in liquid form. Now, NASA scientists have found compelling evidence that liquid water—life-giving, gloriously wet H 20—exists on Mars.
We’re not talking gushing rivers or oceans here. These scientists have been investigating “recurring slope lineae,” patches of precipitated salt that appear to dribble down Mars’ steep slopes like tears rolling gently down a cheek. Planetary scientists hypothesized that the streaky formations were products of the flow of water, but they didn’t have concrete, mineralogical evidence for that idea until now, says Lujendra Ojha, a scientist at Georgia Tech who first spotted the lineae back in 2010. In a new Nature Geoscience paper, published online today, Ojha and his colleagues present “smoking gun validation” that it was liquid water flowing on Mars’ surface that formed these tear stains.
Ojha and his team have watched these lineae form every Martian summer, growing wider week after week until they slowly fade come winter—exactly the times and places where conditions are right for liquid water to exist on Mars. Plus, the surface is crusted with salt, which could help stabilize liquid water so it doesn’t boil or freeze.
Ojha notes that they haven’t actually observed water flowing on Mars. The team took their data from the CRISM instrument on the Mars Reconnaisance Orbiter, which, frustratingly, only observes the surface every day at 3 pm. That’s when Mars is at its hottest and driest, so any liquid water oozing on the surface would have long since evaporated by the time MRO laid eyes on it.
Still, the water left a distinctive chemical trace. “Whatever is flowing on Mars is hydrating the salt,” Ojha says, “and we’re seeing that hydration in the spectral signature.” After extracting spectral information from pixels of the CRISM instrument’s data, Ojha and his team determined that the salts—magnesium perchlorate, magnesium chlorate, and sodium perchlorate—had water molecules interspersed in their crystal structures. That’s pretty strong evidence that they were deposited by flowing water.
The team doesn’t know where the water is coming from, or how much of it there is yet. “That’s the big mystery right now,” Ojha says. They have ideas, though: Maybe the ice inside Mars is melting and percolating out, or maybe a subterranean network of aquifers is feeding water to the surface. Right now, NASA’s favorite explanation is deliquescence, in which the salts grab moisture from Mars’ atmosphere to create liquid water.
Either way, this is exciting evidence that Mars could potentially support life—including human life, if Earthlings ever figure out how to colonize the place. NASA is already thinking up potential uses for the water in a future settlement: Scientists could use the hydrogen and oxygen in H2O to make rocket fuel, or water plants in greenhouses, or keep colonists hydrated (important). “The resources are there,” says John Grunsfeld, a science mission administrator at NASA.
Plus, now that they know Mars has liquid water, scientists can narrow down the best places to look for life and direct their next rover, scheduled for 2020, to collect samples at those places. Which, in the long term, will get scientists closer to finally figuring out if life exists on other planets.
This story has been updated to include information from a NASA press conference.
Some of the earliest missions to Mars revealed a planet with a watery past. Pictures beamed back to Earth in the 1970s showed a surface crossed by dried-up rivers and plains once submerged beneath vast ancient lakes. Earlier this year, Nasa unveiled evidence of an ocean that might have covered half of the planet’s northern hemisphere in the distant past.
But occasionally, Mars probes have found hints that the planet might still be wet. Nearly a decade ago, Nasa’s Mars Global Surveyor took pictures of what appeared to be water bursting through a gully wall and flowing around boulders and other rocky debris. In 2011, the high-resolution camera on Nasa’s Mars Reconnaissance Orbiter captured what looked like little streams flowing down crater walls from late spring to early autumn. Not wanting to assume too much, mission scientists named the flows “recurring slope lineae” or RSL.
Researchers have now turned to another instrument on board the Mars Reconnaissance Orbiter to analyse the chemistry of the mysterious RSL flows. Lujendra Ojha, of Georgia Institute of Technology in Atlanta, and his colleagues used a spectrometer on the MRO to look at infrared light reflected off steep rocky walls when the dark streaks had just begun to appear, and when they had grown to full length at the end of the Martian summer.
Writing in the journal Nature Geosciences, the team describes how it found infra-red signatures for hydrated salts when the dark flows were present, but none before they had grown. The hydrated salts – a mix of chlorates and perchlorates – are a smoking gun for the presence of water at all four sites inspected: the Hale, Palikir and Horowitz craters, and a large canyon called Coprates Chasma.
“These may be the best places to search for extant life near the surface of Mars,” said Alfred McEwen, a planetary geologist at the University of Arizona and senior author on the study. “While it would be very important to find evidence of ancient life, it would be difficult to understand the biology. Current life would be much more informative.”
The flows only appear when the surface of Mars rises above -23C. The water can run in such frigid conditions because the salts lower the freezing point of water, keeping it liquid far below 0C.
“The mystery has been, what is permitting this flow? Presumably water, but until now, there has been no spectral signature,” Meyer said. “From this, we conclude that the RSL are generated by water interacting with perchlorates, forming a brine that flows downhill.”
John Bridges, a professor of planetary science at the University of Leicester, said the study was fascinating, but might throw up some fresh concerns for space agencies. The flows could be used to find water sources on Mars, making them prime spots to hunt for life, and to land future human missions. But agencies were required to do their utmost to avoid contaminating other planets with microbes from Earth, making wet areas the most difficult to visit. “This will give them lots to think about,” he said.
For now, researchers are focused on learning where the water comes from. Porous rocks under the Martian surface might hold frozen water that melts in the summer months and seeps up to the surface.
Another possibility is that highly concentrated saline aquifers are dotted around beneath the surface, not as pools of water, but as saturated volumes of gritty rock. These could cause flows in some areas, but cannot easily explain water seeping down from the top of crater walls.
A third possibility, and one favoured by McEwen, is that salts on the Martian surface absorb water from the atmosphere until they have enough to run downhill. The process, known as deliquescence, is seen in the Atacama desert, where the resulting damp patches are the only known place for microbes to live.
“It’s a fascinating piece of work,” Bridges said. “Our view of Mars is changing, and we’ll be discussing this for a long time to come.”