Intriguing dark streaks on Mars may be caused by landslides after all
Science & Technology

Intriguing dark streaks on Mars may be caused by landslides after all

The cause of the dark streaks on some Martian slopes known as recurring slope lineae, imaged here by NASA’s Mars Reconnaissance Orbiter, is a topic of considerable debate. Some scientists think temporary surface flows of salty water are responsible, and others consider landslides a more likely explanation.

(Image: © NASA/JPL-Caltech/Univ. of Arizona )

Martian landslides might help explain mystery lines seen on the surface of the Red Planet, a new study finds.

For years, scientists analyzing the Martian surface have detected clusters of dark, narrow lines that seasonally appear on steep, sun-facing slopes in the warmer regions. Previous research has suggested that these enigmatic dark streaks, called recurring slope lineae (RSL), are signs that salty water regularly flows on the Red Planet during its warmest seasons.

Recent missions to Mars have revealed that the planet does possess huge underground pockets of ice. Prior work suggested that warmer temperatures during the Martian spring and summer could help generate salty brines capable, at least for a time, of staying liquid in the cold, thin air of the Red Planet.

Related: The search for water on Mars in pictures

However, geologists have discovered problems with the concept of brines causing RSL, explained study lead author Janice Bishop, a planetary scientist at the SETI (Search for Extraterrestrial Intelligence) Institute and NASA Ames Research Center, both of which are in California’s Silicon Valley. For example, the angle of slopes where RSL occur and the features surrounding where they start “largely are inconsistent with a liquid flow process,” she told Space.com.

Now Bishop and her colleagues suggest that chemical reactions could make the Martian surface vulnerable to landslides that might explain RSL.

“Although the surface of Mars today is dry and harsh and cold and dominated by wind and abrasion, underneath the surface, micro-scale interactions of salts with tiny ice and liquid water particles can be still occurring today,” Bishop said.

The scientists focused on chemical reactions between sulfate minerals such as gypsum with chloride salts, of which table salt is one variety. “On Earth, interactions between gypsum and chloride salts have caused collapse of parts of caves, sinkholes in soft sediments near salty lakes and ponds, and uplift of roads,” Bishop said.

The researchers speculated that similar interactions could happen on Mars, although the cold and dry conditions there would slow these reactions down. “I am super excited about the prospect of active chemistry below the surface on Mars, albeit at a slow rate,” Bishop said.

In the new study, the scientists conducted lab experiments on mixtures of sulfates, chloride salts, tiny ice particles and volcanic ash similar to Martian soil. They froze and thawed such mixtures at the kinds of low temperatures found on the Red Planet.

The researchers found thin films of slushy water formed on the surfaces of the mineral grains. They suggested these films could expand and contract over time, leading to upheavals and contractions under the Martian surface. Wind and dust on these unstable surfaces could then set off landslides, producing the lines seen on the Red Planet, Bishop explained.

The scientists noted that in the future, surface missions on Mars to recent RSL sites could help test their model. They detailed their findings online today (Feb. 3) in the journal Science Advances.

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