On some Martian slopes, in the warmer months, dark streaks appear. They are known as Recurring Slope Lineae or RSL and they were first thought to be a rare example of flowing, briny water on Mars. This claim was re-adjusted after follow-up observations pointed out that the flow behaved like sand, although it couldn't explain the seasonal nature of them. Now, a new hypothesis tries to bridge the two.
As reported in Science Advances, the new study suggests that salt and melting ice could affect the terrain leading to the formation of the landslides we detected as RSL. Instead of flowing water, the team believes that small-scale interactions between water ice, chlorine salts, and sulfates produce a slush when temperature increase during the Martian summer. This briny slush can instigate ground collapse and upheaval, leading to a surface flow of dust and sand. In other words, a landslide.
“I am excited about the prospect of microscale liquid water on Mars in near-surface environments where ice and salts are mixed with the soil,” lead author and SETI Institute scientist Dr Janice Bishop said in a statement. “This could revolutionize our perspective on active chemistry just below the surface on Mars today.”
Over the last five years, researchers considered how terrain on Earth could reproduce what we are seeing on Mars. The most likely scenario is that the RSL is unique to the Red Planet’s environment but we can still learn something from the extreme terrain of the McMurdo Dry Valleys of Antarctica, the Dead Sea in Israel, and the Salar de Pajonales (salt flats) in the Atacama Desert, Chile.
In those dry, salt-rich environments, a bit of subsurface water can cause surface disruption and landslides. The team took these observations further by creating a Mars soil analog in the lab. This concoction was frozen and then thawed slowly. The team reported slushy ice forming at -50°C (-58°F), followed by the gradual melting of the ice from -40°C to -20°C (-40°F to -4°F).
“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 Merve Ye?ilba?, NASA Postdoctoral (NPP) Fellow at the SETI Institute.
This scenario is certainly intriguing and it has some support, but more evidence will be necessary to confirm that this is indeed the mechanism behind the mysterious RSL.