Using an imaging spectrometer on NASA’s Mars Reconnaissance Orbiter, agency’s planetary scientists have detected signatures of hydrated minerals on warm slopes where intriguing seasonal flows, called recurring slope lineae, are seen on Mars.
This image of an impact crater in the Sirenum Fossae region of Mars was taken by NASA’s Mars Reconnaissance Orbiter on March 30, 2015. The crater is approximately 3,300 feet (1-km) wide and appears relatively recent as it has a sharp rim and well-preserved ejecta. The steep inner slopes are carved by gullies and include possible recurring slope lineae on the equator-facing slopes. Image credit: NASA / JPL / University of Arizona / Alfred McEwen.
“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 Dr John Grunsfeld, a former astronaut who now leads NASA’s Science Mission Directorate.
“This is a significant development, as it appears to confirm that water – albeit briny – is flowing today on the surface of Mars.”
Recurring slope lineae appear in several locations on the Red Planet when temperatures are above minus 10 degrees Fahrenheit (minus 23 Celsius), and disappear at colder times.
Recurring slope linea on the south-facing slope of a crater on the floor of Melas Chasma, Mars. Image credit: McEwen AS et al / NASA / JPL-Caltech / University of Arizona.
They often have been described as possibly related to liquid water. The new findings, published in the journal Nature Geoscience, 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. It’s likely a shallow subsurface flow, with enough water wicking to the surface to explain the darkening,” the scientists said.
Recurring slope linea on north-facing slopes in Coprates Chasma, Mars. Image credit: McEwen AS et al / NASA / JPL-Caltech / University of Arizona.
“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,” said lead author Lujendra Ojha, a Ph.D. student at the Georgia Institute of Technology.
“In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks.”
He first noticed recurring slope lineae in 2010, using images from the High Resolution Imaging Science Experiment (HiRISE) on board the Mars Reconnaissance Orbiter (MRO).
The new study pairs HiRISE observations with mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars.
Recurring slope lineae emanating from bedrock exposures at Palikir crater on Mars during southern summer. Image credit: Lujendra Ojha et al / Geophysical Research Letters.
The observations show signatures of hydrated salts at multiple locations of recurring slope lineae, but only when the features were relatively wide.
When Ojha and co-authors looked at the same locations and recurring slope lineae weren’t as extensive, they detected no hydrated salt.
These dark, narrow, 100 meter-long recurring slope lineae flowing downhill on Mars are inferred to have been formed by contemporary flowing water. Recently, scientists detected hydrated salts on these slopes at Hale crater, corroborating their original hypothesis that the streaks are indeed formed by liquid water. The blue color seen upslope of the dark streaks are thought not to be related to their formation, but instead are from the presence of the mineral pyroxene. Image credit: NASA / JPL / University of Arizona.
They 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.
“When most people talk about water on Mars, they’re usually talking about ancient water or frozen water. Now we know there’s more to the story,” Ojha said.
“This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for recurring slope lineae.”
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Lujendra Ojha et al. 2015. Spectral evidence for hydrated salts in recurring slope lineae on Mars. Nature Geoscience, published online September 28, 2015; doi: 10.1038/ngeo2546
