We’re not talking water that flowed 2 billion years ago, but water that might be flowing right now. Scientists announced today they had discovered strong evidence for salt water seeps flowing on Mars called recurring slope lineae – RSL for short. The Mars Reconnaissance Orbiter (MRO) has taken hundreds of pictures of so-called “slope streaks” for years on many different locations on the planet from the equator through the middle latitudes, While they appear to be created by flowing water, there was no way to be sure it wasn’t moving sand or even flows related to vaporizing carbon dioxide ice.
The narrow streaks measure just 1.6 -16 feet (0.5 to 5 meters) wide but can extend for hundreds of yards (meters) downslope of cliffs, crater walls and mountains. They ebb and flow over time, darkening and appearing to flow down steep slopes during Martian summers and then fading away in the fall and winter. Some have been spotted in several locations on the planet when temperatures are above -10 F (-23 C), but disappear when it gets colder.
“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 published today in Nature Geoscience.
Using an imaging spectrometer on MRO, researchers detected signatures of salty minerals bound up with water (hydrated salts) on the slopes where mysterious streaks are seen on the Red Planet. Water, the unsalted variety, would quickly freeze or boil away in Mars’ extremely low atmospheric pressure and bitter cold temperatures. Freshwater on Earth freezes at the familiar 32 F (0 C), but the salt in seawater lowers water’s freezing temperature to 28.4 F. Putting salt on the roads during winter has the same effect – making the ice melt (turn into liquid water) more rapidly.
Similarly on Mars, Ojha and colleagues found evidence in the slope streaks of hydrated minerals called perchlorates using MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). 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° F (-70° C). On Earth, naturally produced perchlorates are concentrated in deserts, and some types of perchlorates can be used as rocket propellant.
This animation simulates a fly-around look at one of the places on Mars where dark streaks advance down slopes during warm seasons, possibly involving liquid water. This site is within Hale Crater. The streaks are roughly the length of a football field.
“Our quest on Mars has been to ‘follow the water,’ in our search for life in the universe, and now we have convincing science that validates what we’ve long suspected,” said John Grunsfeld, astronaut and associate administrator of NASA’s Science Mission Directorate in Washington. “This is a significant development, as it appears to confirm that water — albeit briny — is flowing today on the surface of Mars.”
So the question is whether something could survive in briny waters. Of course! Bacteria have been on Earth deep in South African mines thousands of feet below the surface and far removed from sunlight quietly going about their lives in hot, salty water. If Earth, Mars? Maybe. We won’t know until we send a probe to collect samples. Now that we’re reasonably sure these flows are salt water, perhaps one of the denser networks of streaks will become a future landing site.