Lines on Mars could be created by salty water triggering landslides

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Martian surface

The Krupac crater on Mars featuring gullies along the rim and “recurring slope lineae” lower down the crater wall

NASA/JPL/University of Arizona

For years, researchers have been arguing about whether strange streaks on the Martian surface are caused by flowing water or sliding dust. The real answer may combine both.

Recurring slope lineae (RSLs) are dark stripes that appear to flow down the sides of craters on Mars during the warmest parts of the year. Janice Bishop at the SETI Institute in California and her colleagues were studying the strange behaviour of salty sediments in Antarctica when they realised that similar processes could cause RSLs on Mars.

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They used soils similar to those found on Mars to test their idea. When they added a small amount of water, it percolated through the soil and brought salts up to the surface. These created a crust with pockets of air beneath it that formed as the salts expanded with water and then contracted again.

“It’s like a seasoning mix with salt in it: just a little bit of water and it sticks to everything and gets all crusty and stuck in the shaker,” says Bishop.

Recent observations of the Martian surface have shown that RSLs are more likely to occur after dust storms. Dumping dust on thin, salty crusts could cause them to collapse into the air pockets beneath them. That collapse could then trigger more dust to slide downhill, causing what we see as RSLs.

“If you’ve got these crusts forming and also these sinkholes and gaps, that could make these really weird unstable surfaces,” says Bishop. “Then if you have a fragile surface and it’s being sandblasted and covered in dust by a storm, that’s a good way to start a landslide.”

“The whole RSL story is complicated because we are not there and we can’t test it,” says Bishop. The rovers that have been on Mars can only dig a few centimetres under the surface, so can’t tell us anything about the possibilities of processes like the one Bishop and her colleagues suggest could cause RSLs.

However, the Rosalind Franklin rover, planned to launch in 2022, will have the capability to dig deeper, so it may be able to solve the mystery.

Journal reference: Science Advances, DOI: 10.1126/sciadv.abe4459

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