New findings from NASA’s Mars Reconnaissance Orbiter (MRO) provide the strongest evidence yet that liquid water flows intermittently on present-day Mars.
NASA researchers using an imager aboard the Mars Reconnaissance Orbiter confirmed the watery flows by looking at light waves returned from seasonal dark streaks on the surface, long suspected to be associated with liquid water.
They detected signatures of hydrated minerals on slopes where mysterious streaks are seen on the Red Planet. These darkish streaks appear to ebb and flow over time. They darken and appear to flow down steep slopes during warm seasons, and then fade in cooler seasons. They appear in several locations on Mars when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times.
It remains unclear where the water comes from. Theories include deliquescence, melting subsurface ice or even a liquid-water aquifer that feeds the process. Discovering what precisely is causing the phenomenon is a mystery for the next round of investigations, said Michael Meyer, lead scientist for NASA’s Mars Exploration Program.
This is not the first discovery of water on Mars. Researchers have known for many years that Mars has water frozen at its poles, in its thin atmosphere, and, most recently, in tiny puddles that appear to form at night on the surface.
These downhill flows, known as recurring slope lineae (RSL), often have been described as possibly related to liquid water. The new findings of hydrated salts on the slopes point to what that relationship may be to these dark features. The hydrated salts would lower the freezing point of a liquid brine, just as salt on roads here on Earth causes ice and snow to melt more rapidly. Scientists say it’s likely a shallow subsurface flow, with enough water wicking to the surface to explain the darkening.
“We found the hydrated salts only when the seasonal features were widest, which suggests that either the dark streaks themselves or a process that forms them is the source of the hydration. In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks,” said Lujendra Ojha of the Georgia Institute of Technology (Georgia Tech) in Atlanta, lead author of a report on these findings published Sept. 28 by Nature Geoscience.
Ojha first noticed these puzzling features as a University of Arizona undergraduate student in 2010, using images from the MRO’s High Resolution Imaging Science Experiment (HiRISE). HiRISE observations now have documented RSL at dozens of sites on Mars. The new study pairs HiRISE observations with mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).
The spectrometer observations show signatures of hydrated salts at multiple RSL locations, but only when the dark features were relatively wide. When the researchers looked at the same locations and RSL weren’t as extensive, they detected no hydrated salt.
Ojha and his co-authors interpret the spectral signatures as caused by hydrated minerals called perchlorates. The hydrated salts most consistent with the chemical signatures are likely a mixture of magnesium perchlorate, magnesium chlorate and sodium perchlorate. Some perchlorates have been shown to keep liquids from freezing even when conditions are as cold as minus 94 degrees Fahrenheit (minus 70 Celsius). On Earth, naturally produced perchlorates are concentrated in deserts, and some types of perchlorates can be used as rocket propellant.
Perchlorates have previously been seen on Mars. NASA’s Phoenix lander and Curiosity rover both found them in the planet’s soil, and some scientists believe that the Viking missions in the 1970s measured signatures of these salts. However, this study of RSL detected perchlorates, now in hydrated form, in different areas than those explored by the landers. This also is the first time perchlorates have been identified from orbit.
MRO has been examining Mars since 2006 with its six science instruments. “The ability of MRO to observe for multiple Mars years with a payload able to see the fine detail of these features has enabled findings such as these first identifying the puzzling seasonal streaks and now making a big step towards explaining what they are,” said Rich Zurek, MRO project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.
For Ojha, the new findings are more proof that the mysterious lines he first saw darkening Martian slopes five years ago are, indeed, present-day water.”When most people talk about water on Mars, they’re usually talking about ancient water or frozen water,” he said. “Now we know there’s more to the story. This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for RSL.”
The discovery is the latest of many breakthroughs by NASA’s Mars missions.
“It took multiple spacecraft over several years to solve this mystery, and now we know there is liquid water on the surface of this cold, desert planet,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at the agency’s headquarters in Washington. “It seems that the more we study Mars, the more we learn how life could be supported and where there are resources to support life in the future.”
“The existence of liquid water, even if it is super salty briny water, gives the possibility that if there is life on Mars, that we have a way to describe how it might survive,” said John Grunsfeld, associate administrator for the Science Mission Directorate at NASA.
It remains to be seen whether the new discovery improves the odds of life on Mars, but researcher Mary Beth Wilhelm said the results suggest “more habitable conditions on the near surface of Mars than previously thought.” How habitable, she said, depends on how salty and how cold the conditions are.
Alfred McEwen, who heads up NASA’s HiRISE high-resolution camera aboard the Mars orbiter, said he is fairly confident life will one day be found on Mars. “It’s very likely, I think, that there is life somewhere in the crust of Mars, microbes,” he said.
While the discovery doesn’t by itself offer evidence of life on Mars, either past or present, it does boost hopes that the harsh landscape still offers some refuge for microbes to cling to existence.
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