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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Geologists have discussed the odd behaviour of martian landslides since they were first identified nearly half a century ago
‘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 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.
Mars Reconnaissance Orbiter (MRO) camera view of Krupac crater on Mars featuring gullies along the rim and RSL lower down the crater wall.
On Earth, only seeping water is known to have these behaviours, but how they form in the dry Martian environment remains unclear.
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.
Infrared spectroscopy revealed that thin layers of liquid-like water were forming along grain surfaces 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.
Subsurface permafrost contains water ice, and chemical alteration appears to be occurring below the surface
Mars soil analog material covering calcium sulfate and calcium chloride from below, absorption of water by salts and soil particles, migration of the salts towards the surface, and formation of crust with cavities
As on Mars, the Dry Valleys’ surface regolith is scoured by dry winds most of the year.
However, subsurface permafrost contains water ice, and chemical alteration appears to be occurring below the surface.
‘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.
More recently, High Resolution Imaging Science Experiment (HiRISE) data from MRO has captured views of this near-surface ice at mid-latitudes.
Warmer temperatures (around -50°C to -20 °C) at equatorial sites on Mars could support subsurface liquid water and brines during spring and summer months.
The research paper has been published today in Science Advances.
WHAT IS THE MARS RECONNAISSANCE ORBITER?
The Mars Reconnaissance Orbiter (MRO) searches for evidence that water persisted on the surface of Mars for a long period of time.
It was launched August 12, 2005, and achieved an initial orbit around the red planet on March 10, 2006.
In November 2006, after five months of, it entered its final science orbit and began its primary science phase.
Since its arrival, MRO and its High Resolution Imaging Science Experiment (HiRISE) telescope have been mapping the martian surface, which has been taking shape for more than three billion years.
MRO’s instruments analyse minerals, look for subsurface water, trace how dust and water are distributed in the atmosphere, and monitor daily weather in support of its science objectives.
MRO’s missions have shown that water flowed across the Martian surface, but it is still unknown whether water persisted long enough to provide a habitat for life.