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Published: 2021-08-03

Martian landslides caused by salts and melting ice?

NEWS A group of researchers at the SETI Institute NASA Astrobiology Institute, in which Umeå chemist Merve Yeşilbaş participates, presents a theory of what causes landslides on the surface of Mars. The results have been published in the journal Science Advances.

Text: Ingrid Söderbergh

The red planet Mars is today a frozen desert and has no stable liquid water on the surface. Nevertheless, the latest research gives hope for other types of water forms on Mars.

Previous research has suggested that liquid debris or dry granular flows cause earth movements on Mars, so-called Marsian gullies. However, none of these models take into account the seasonal landslide formation on the planet called Recurring Slope Lineae, RSL.

Researchers from NASA and Umeå University instead assume that the small-scale melting of ice in the regolith near the ground surface causes changes at the surface that make it exposed to dust storms and wind. As a result, the RSL functions expand on the surface of Mars, ie small ravines are formed. Furthermore, the researchers believe that the thin layers of melting ice are due to interactions between underground water ice, chlorine salts and sulphates, which creates an unstable and liquid-like liquid sludge that gives rise to sinkholes, soil collapse, surface flows and landslides.

“The results revolutionize our perspective on active chemistry just below the surface of Mars” says Janice Bishop, who has led the study and is a researcher at the SETI Institute NASA Astrobiology Institute in the USA.

Geochemistry studied on earth

Analogous sites on Earth are used in space exploration to study geochemical conditions on Mars. Examples are the dry valleys of Antarctica, the Dead Sea in Israel and the Salar de Pajonales in the Atacama Desert. Previous observations in Northern Chile have shown that when salts interact with gypsum or water below the ground, it causes geological disturbances and causes collapse and landslides.

To test the research group's theory, the chemist Merve Yeşilbaş conducted experiments with low temperature vibration spectroscopy at Umeå University. She observed what happens if you freeze and thaw Mars-analogous soil samples (volcanic soil collected from Hawaii) consisting of chlorine salts and sulfates at the low temperatures found on Mars. The result was a sludge-like ice formation at near -50° C, followed by gradual melting of the ice from -40 to -20° C.

“My lab experiments reveal that thin layers of liquid water form along grain surfaces when the salty soil samples thaw under Mars-like temperatures. Possible presence of thin water films below the surface of Mars in saline permafrost regions suggests that chemical activity may still be possible on Mars today” says Merve Yeşilbaş, postdoctoral fellow at the Department of Chemistry at Umeå University with support from the Swedish Research Council and NASA Postdoctoral Programme SETI Institute.

Salts move water molecules

Modeling the behavior of chlorine salts and sulfates, including gypsum, at low temperatures also shows how interconnected the salts are. It may be that the liquid water on a micro-scale migrates below the earth's surface on Mars and transfers water molecules between the sulphates and the chlorides, much like a football team moves the ball down the field. In additional laboratory experiments at the SETI Institute, the sulfate chloride reactions were tested in Mars analogous soil samples from the dry valleys of McMurdo in Antarctica with color indicators, which revealed hydration of the salts on the surface and salt migration through the soil grains.

Water ice has been discovered below the surface of Mars in soil excavated at the landing site in Phoenix, as well as from orbit using radar measurements and with neutron and gamma ray spectroscopy. Recently, ice has been detected with a HiRISE camera near the surface in regions near the equator on Mars. The ice in these areas is not thick and the permafrost there is expected to contain frozen soil with small ice grains surrounding mineral and soil particles.

Warmer temperatures during the spring and summer months (-50 to -20° C) at the equatorial locations on Mars could cause the ice to melt into a liquid-like sludge. RSLs observed at some of these sites are often interpreted to be related to Marsian gullies, which resemble small ravines or ditches on Earth.

Dynamic environment on Mars

In addition to helping to explain Mars' geological and chemical processes, the researchers' findings also show that the environment on Mars remains dynamic - that the planet is still evolving and active - which has implications for both astrobiology and future human exploration of the red planet. The results of the research group can revolutionize our perspective on active chemistry just below the surface of Mars.

"In addition, these results are important not only for planetary science and astrobiology but also for understanding the cold environments on Earth, such as the Arctic and Antarctic" says Merve Yeşilbaş.

Original article:
Bishop, J. L. et al: Martian Subsurface Cryosalt Expansion and Collapse as Trigger for Landslides. Science Advances 7 (2021). https://advances.sciencemag.org/content/7/6/eabe4459

Press photos

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For more information, please contact:

Merve Yesilbas
Assistant professor