September 28, 2015

— Salty liquid water may be flowing down hills on Mars, countering the image of a long dried-up planet, and bolstering the possibility that life may exist there today.

Researchers, using an imaging spectrometer on NASA's Mars Reconnaissance Orbiter (MRO), detected signatures of hydrated minerals on slopes where mysterious streaks have been seen on the Red Planet, NASA announced on Monday (Sept. 28). These darkish streaks appear to ebb and flow over time, darkening and appearing to flow down steep slopes during warm seasons, and then fading in the cooler seasons.

These streaks have been observed in several locations on Mars when temperatures are above minus 10° Fahrenheit (minus 23° Celsius), and disappear at colder times.

"This is a significant development as it appears to confirm that water — albeit briny — is flowing today on the surface of Mars," said John Grunsfeld, a former astronaut and the associate administrator of NASA's science directorate.

"I grew up during the era when Viking had landed on Mars and revealed a desert-like planet, apparently dead and not this interesting as we see it really is," he stated. "[This] is most exciting because it suggests it would be possible for there to be life today on Mars."

False color image showing recurring slope lineae flowing down the slopes of Hale crater on Mars. The blue color seen upslope of the dark streaks are thought not to be related to their formation, but instead are from the mineral pyroxene. (NASA/JPL/UA)

The downhill flows, known as recurring slope lineae (RSL), have been believed to be possibly related to liquid water since they were first detected in 2010. The new findings of hydrated salts on the slopes point to what that relationship may be to these dark features.

The salts lower the freezing point of a liquid brine, just as salting roads on Earth cause ice and snow to melt more rapidly. Scientists have described the RSL as likely being a shallow subsurface flow, with just enough water wicking to the surface to explain the darkening.

"What we're dealing with is wet soil, thin layers of wet soil, not standing water," Alfred McEwen, principal investigator for HiRISE (High Resolution Imaging Science Experiment) at the University of Arizona in Tucson, said on Monday.

The hydrated salts were found 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," explained Lujendra Ojha of the Georgia Institute of Technology, the lead author of a report on the findings in the Sept. 28 issue of Nature Geoscience.

Ojha first noticed these features five years ago when he was a University of Arizona undergraduate student, using images from the MRO's HiRISE. Subsequent observations have now documented RSL at dozens of sites on Mars. The new study pairs the HiRISE observations with mineral mapping by the reconnaissance imaging spectrometer on MRO (CRISM).

Dark, narrow streaks emanating out of the walls of Garni crater on Mars, thought to be the flow of briny water. (NASA/JPL/UA)

Ojha and his co-authors interpret the spectral signatures as caused by hydrated minerals called perchlorates. The hydrated salts that are 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 (minus 70° C). On Earth, naturally produced perchlorates are concentrated in deserts, and some types 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 other areas than those explored by the landers.

This also is the first time perchlorates have been identified from orbit.

"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."

Enlarge and view the video in new pop-up window. (NASA TV)

For now, those future studies will continue from orbit and afar, less they contaminate the sites with terrestrial life.

"This is why we are crawling before we walk, so to speak," Grunsfeld said. "We are being very careful that we do not send a spacecraft with the intention of detecting Martian life and find out we detected Earth life we took with us."

Though there is a possibility that Curiosity could observe what might be briny streaks near where it is already set to rove, given the planetary protection concerns and location of features, it is more likely that a specially-designed rover will be needed.

"These streaks of briny water are in challenging locations. Some of these briny features are on very steep slopes in tough terrain. It would be trivial for an astronaut to go up and investigate but very hard for a rover. So we're a little ways off," said Grunsfeld.

"The investigation of these [streaks] with proper planetary protection lays in the domain of future robotic spacecraft that are designed to specifically go there [and] in a way that they can be appropriately sterilized," Grunsfeld said. "The exciting thing about this announcement... [is] that I think [it] will really drive the ingenuity of our engineers and scientists to come up with a viable experiment, hopefully [one] we can do in the 2020s, and we can go investigate these areas and perhaps even return samples."