On Mars, seasonal features known as recurring slope lineae (RSL) are prevalent on Sun-facing slopes. Previous studies have suggested RSL are related to chlorine salts and noted their occurrence in regions of high sulfate outcrops. New laboratory experiments demonstrate that interactions of sulfates and chlorine salts in fine-grained soils on the Red Planet could absorb water, expand, deliquesce, cause subsidence, form crusts, disrupt surfaces, and ultimately produce landslides after dust loading on these unstable surfaces.
HiRISE camera view of Krupac crater on Mars featuring gullies along the rim and recurring slope lineae lower down the crater wall. Image credit: NASA / JPL / University of Arizona.
“I am excited about the prospect of microscale liquid water on Mars in near-surface environments where ice and salts are present,” said lead author Dr. Janice Bishop, a researcher in the Carl Sagan Center at the SETI Institute and the Space Science and Astrobiology at NASA’s Ames Research Center.
“This could revolutionize our perspective on habitability just below the surface on Mars today.”
“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,” added co-author Professor Nancy Hinman, a researcher in the Department of Geosciences at the University of Montana.
“It’s gratifying to find that it could play a role in shaping Mars as well.”
The scientists conducted lab experiments to observe what would occur if they froze and thawed Mars analog samples comprised of chlorine salts and sulfates at low temperatures such as would be found on the Red Planet.
The result was slushy ice formation near minus 50 degrees Celsius, followed by gradual melting of the ice from minus 40 to minus 20 degrees Celsius.
“Probing the low-temperature behavior of Mars analog permafrost in the lab with infrared spectroscopy revealed that thin layers of liquid-like water were forming along grain surfaces as the salty soils thawed under subzero, Mars-like temperatures,” said co-author Dr. Merve Yeşilbaş, a researcher in the Carl Sagan Center at the SETI Institute and the Department of Chemistry at Umeå University.
Modeling the behavior of chlorine salts and sulfates, including gypsum, under low temperatures demonstrates how interrelated these salts are.
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 a Mars analog soil with color indicators that revealed subsurface hydration of these salts and the migration of salts through the soil grains.
“I was thrilled to observe such rapid reactions of water with sulfate and chlorine salts in our lab experiments and the resulting collapse and upheave of Mars analog soil on a small scale, replicating geologic collapse and upheave features in karst systems, salt reservoirs, and edifice collapse on a large scale,” Dr. Bishop said.
The research is published in the journal Science Advances.
J.L. Bishop et al. 2021. Martian subsurface cryosalt expansion and collapse as trigger for landslides. Science Advances 7 (6): eabe4459; doi: 10.1126/sciadv.abe4459