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And then there’s the mystery of Recurring Slope Lineae, known as RSL, which has puzzled scientists for years. These RSLs are a form of landslide on Mars, but no one knows what causes them, said Janice Bishop, author of a new study on the phenomena.
“We see them from their orbit by the dark streaks they produce on the ground and they tend to always occur on slopes exposed to the sun, which has led geologists to believe they were linked to the melting of the ice cream early on, ”said Bishop, principal investigator at the SETI Institute in California.
“What’s interesting is that they increase over the months after dust storms and then go away, and they seem to form over and over in the same areas. Plus, a lot of them do. in the equatorial part of Mars, where there is very little ice. “
Any ice in these regions should be tiny frozen particles that exist between the soil grains below the surface.
These puzzling landslides have never been seen up close by a rover or lander, and until they can be studied by a robotic explorer, scientists are using laboratory experiments and Martian analogues on Earth to try to understand them.
Some of the strange environments on Earth that are similar to that of Mars include the Atacama Desert in Chile, parts of Antarctica, and even the Dead Sea. These locations show that surface collapse and landslides occur when salt interacts with sulfates or groundwater.
“Antarctica and Atacama are great analogues for Mars because they are ultra dry environments,” Bishop said. “Antarctica has the added advantage that it is very cold. Parts of Antarctica, including Beacon Valley, are actually tied with Mars for temperature and aridity.”
While water may once have been plentiful on the Martian surface billions of years ago, when the planet was warmer and still retained most of its atmosphere, the current surface of Mars is a frigid landscape and sterile.
What is below
However, missions to Mars and imagery by orbiters have revealed that the frozen salt water lies below the surface – and that the water could lead to activity that appears on the Martian surface, such as landslides.
Bishop and his colleagues collected samples from some similar environments on Earth, including the Wright Valley in Antarctica, to test how salts and melting ice underground could cause chemical reactions that trigger these seasonal landslides on March. The researchers wanted to test whether processes seen in places like Antarctica, where salty sediment can have an effect on surface soil, could occur on Mars.
Scientists modeled brackish water beneath the surface of Mars in a lab by taking the collected soil samples and exposing them to water, chlorine salts, and sulfates – all of which may exist below the Martian surface. This experiment resulted in the creation of thin and mobile films of muddy water.
To model Martian temperatures where ice exists below the surface at the planet’s mid-latitudes, the researchers found melting ice formed near negative 58 degrees Fahrenheit and slow, gradual melting of the ice between minus 40 degrees Fahrenheit and minus 4 degrees Fahrenheit.
These temperatures may seem cold, but on Mars they are actually considered slightly warmer temperatures near the equator – which could support brackish water below the surface in the Martian spring and summer.
If this subterranean brine on Mars expands and contracts over time on Mars, it could weaken the surface and cause sinkholes, ground collapse and landslides.
Previously, scientists believed that streams of liquid debris or dry grainy material could be the cause of landslides, but neither completely matched what scientists saw in the RSL.
However, if the ice melts just below the surface, this change would also alter the surface itself. The Martian surface is also at the mercy of wind and seasonal dust storms, which could also play a role in this phenomenon.
“During my fieldwork at Salar de Pajonales, a dry salt bed in northern Chile, I observed many examples of the action of salts on the local geology. It’s gratifying that it could also play a role in the formation of Mars, ”study co-author Nancy Hinman, professor of geosciences at the University of Montana, said in a statement.
Chemical activity
“If our hypothesis is correct, then RSL could be indicators for salts on Mars and for near-surface active chemistry,” Bishop said. “Most of us Mars scientists have viewed modern Mars as a cold, dry, dormant place, shaped primarily by dust storms. This is certainly true of the surface, but our work shows that the subsoil could be much more chemically active than previously thought. “
Bishop noted that this underground process that could lead to landslides on the surface would be slow and limited.
Although this brine is too salty to support life, the study’s experiments support the idea that this underground liquid water can actually move around salt and mineral grains. If so, water on Mars 4 billion years ago could have seeped into the subsoil like a type of permafrost soil. This ice could have thawed and refrozen over time.
“It could be that more of that pristine water on Mars persisted longer than we thought below the surface,” Bishop said. “If this is true, it could indicate that the subsoil of Mars was habitable longer than the surface environment. It is difficult to estimate how long, but perhaps liquid water was present around it. grains of the soil below the surface until 3 or 2 billion years ago or even more. recently. “
“Once we send rovers to Mars capable of digging the surface, I think we’ll see signs of salt reactions below the surface – especially if we investigate some of the equatorial regions where RSL occurs,” Bishop said.
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