Martian landslides may be caused by underground salts and melting ice just below the surface of the Red Planet, study claims

• Scientists in the US recreated Martian landslides on a miniature scale in the lab
• These landslides cause dark streaks - features known as Recurring Slope Lineae 
• Thin layers of melting ice result from interactions with chlorine salts and sulfates
• This creates an unstable, liquid-like flowing slush instigating sinkholes and slides

Landslides on Mars during the summer months may be caused by underground salts and melting ice, a new study claims. 

Using imitation Martian soil samples, SETI Institute researchers in the US recreated Martian landslides on a miniature scale in the lab.

The frozen, salty and chlorine-laden samples were thawed under temperatures intended to replicate a Martian summer, resulting in slush and liquid water.   

On Mars, melting ice in regolith – the dusty blanket of sediment on the planet's surface – is due to interactions between chlorine salts and sulfates

This creates an unstable, liquid-like slush leading to sinkholes and ground collapse, leaving noticeable dark streaks, as observed by a NASA orbiter. 

The study suggests Mars has a 'dynamic and active environment' that's still evolving – which has implications for future human exploration of the Red Planet, experts say. 

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Video shows wetting of lab Mars soil, absorption of water by salts and soil particles, migration of the salts towards the surface and formation of crust with cavities 

'I am excited about the prospect of microscale liquid water on Mars in near-surface environments where ice and salts are present,' said study author and SETI Institute senior research scientist Dr Janice Bishop. 

'This could revolutionise our perspective on habitability just below the surface on Mars today.' 

Geologists have discussed the odd behaviour of martian landslides since they were first identified nearly half a century ago. 

They can move at speeds of up to 360 kilometres per hour (around 220 miles an hour) over flat surfaces.    

Previous theories suggested the flow of liquid debris or dry granular materials is the cause of these landslides. 

But neither of these theories can completely account for the seasonal Martian flow features known as Recurring Slope Lineae (RSL).  

RSL are seasonal dark streaks on Mars that extend gradually downhill in warm seasons, then fade away in winter and reappear the next year. 

'Martian landslides can include the RSL and slumps and other sliding debris, but RSL are the best documented versions of these features,' Dr Bishop told MailOnline. 

Many thousands of RSL have been identified in more than 50 rocky-slope areas, from the equator to about halfway to the poles. 

On Earth, only seeping water is known to have these behaviours, but how they form in the dry Martian environment remains unclear. 

'We've thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand,' previously said Colin Dundas of the US Geological Survey's Astrogeology Science Center. 

Some RSL observed near the Martian equator are often interpreted to be related to larger features called gullies, which are similar to ravines on Earth. 

Imagery from NASA's Mars Reconnaissance Orbiter (MRO) has already provided images of RSL that are located on slopes facing the sun, where they continue to appear and can expand over time. 

Previous studies have suggested RSL are related to chlorine salts and have noted their occurrence in outcrops where there are high levels of sulfate.  

GIF from NASA and University of Arizona shows development of RSL at Palikir crater on Mars, as viewed by MRO on six occasions during Mars years 29-30   

Field investigations on Earth, such as in the Dry Valleys of Antarctica, the Dead Sea in Israel, and Salar de Pajonales in the Atacama Desert, have also hinted at this. 

These Earth experiments showed that when salts interact with gypsum or water underground, it causes disruptions on the surface, including collapse and landslides.

'During my fieldwork at Salar de Pajonales, a dry salt bed in Northern Chile, I have observed numerous examples of the action of salts on the local geology,' said study co-author Nancy Hinman at SETI Institute. 

'It's gratifying to find that it could play a role in shaping Mars as well.'

To test their theory, the team conducted lab experiments to observe what would occur if they froze and thawed imitation Mars samples – comprised of chlorine salts and sulfates at low temperatures like those that would be found on Mars. 

The result was slushy ice formation near -50°C, followed by gradual melting of the ice from -40°C to -20°C (saltwater has a lower freezing point normal water). 

Infrared spectroscopy revealed that thin layers of liquid-like water were forming as the salty soils thawed under the sub-zero, Mars-like temperatures.

'Modelling the behaviour of chlorine salts and sulfates, including gypsum, under low temperatures demonstrates how interrelated these salts are,' SETI Institute said in a statement. 

'It may be that this microscale liquid water migrates underground on Mars, transferring water molecules between the sulfates and chlorides, almost like passing a soccer ball down the field.' 

Additional lab experiments tested these sulfate-chloride reactions in an imitation Mars soil with colour indicators, revealing subsurface hydration of these salts and the migration of salts through the soil grains. 

This project arose out of work on sediments from the McMurdo Dry Valleys in Antarctica, one of our planet's coldest and driest regions. 

As on Mars, the Dry Valleys' surface regolith is scoured by dry winds most of the year.  

'Sediments in the Dry Valleys provide an excellent testbed for processes that may be occurring on Mars,' said Zachary Burton, recent graduate of Stanford University and collaborator on the SETI Institute NAI team. 

'The presence of elevated concentrations of sulfates and chlorides a few centimetres below the harsh surface landscape in Wright Valley presents the intriguing possibility that these water-related mineralogical associations and attendant processes could exist on Mars as well.'

Water ice has been detected below the surface on Mars within soil scooped up at where NASA's robotic spacecraft Phoenix landed on Mars in 2008, as well as from orbit using radar measurements and using neutron and gamma ray spectroscopy.  

'Our study tested a frozen soil and we found that chlorine salts still liquefied the tiny frozen bits in the soil, which is closer to the kinds of materials in equatorial regions of Mars where the RSL and slumps are found on Mars,' Dr Bishop told MailOnline. 

'At higher latitudes on Mars blocks of ice are found (e.g. the Phoenix landing site) below the surface and sometimes exposed on the surface, but RSL aren't typically found in these regions.' 

The research paper has been published today in Science Advances.