For centuries after Galileo made the first observations of Mars in 1610, the planet appeared to our Earth eyes as a quiet, dusty, and ultimately, dead planet.
But in the last 50 years, scientists have sent multiple spacecraft to observe the Red Planet up close, revealing Mars is very much an active planet, wracked by continuous geological activity and riven with subsurface canals.
One piece of evidence for this activity is the fact the Martian landscape regularly experiences a form of natural disaster which, here on Earth, has the potential to level cities and block roads: Landslides.
For as long as we have known they occur on Mars, so too have scientists not known their cause. But a new study may have uncovered the reason why this Earth-like feature also occurs on Mars lurking beneath the planet's surface. The findings have major implications for future human missions to explore Mars.
The study was published Wednesday in the journal Science Advances.
HERE'S THE BACKGROUND — In September, 2018 NASA's Mars Reconnoissance Orbiter caught a glimpse of what appeared to be a recent landslide in a crater near a region of the planet called Nili Fossae.
The landslides were formed by large amounts of rock and soil moving downslope at a speed of up to 360 kilometers per hour, and extending for over tens of kilometers.
However, scientists were not sure what caused the landslides to form.
WHAT'S NEW — Janice Bishop, senior research scientist at the SETI Institute and lead author behind the new study, was studying the unusual chemical processes which take place beneath Antarctica's ice when she noticed a strange similarity to Mars.
"Antartica is a cold and dry environment like Mars," Bishop tells Inverse.
"So we started looking at other analogs as well to try to understand this chemistry."
Bishop and her team studied both the Dead Sea in Israel and Salar de Pajonales in the Atacama Desert, in addition to conducting experiments in the lab, to glean further insights as to what may be occurring on Mars to cause changes in the planet's topography.
Through their observations, they found that specific chemical salts interact with gypsum, or water underground, and this causes disruptions on the surface, including ground collapse and landslides.
"The chlorine salts are very deliquescent, they absorb a lot of water like a sponge so they become a liquid," Bishop explains. This is similar to a more terrestrial, and familiar process you can see in your own kitchen, she says.
"If you leave your salt shaker out, it absorbs water, and becomes sticky."
Similarly, the chlorine salt and sulfate found in the icy underground water beneath Mars' surface creates an unstable, liquid-like slush which causes disturbances in the above ground surface.
This same process may have also caused landslides to take place on Earth millions of years ago. However, since then, our planet was covered by oceans and plants which covered its surface, preventing us from observing the markings leftover by early processes on the planet.
Why do we study Mars?
"I think Mars is really interesting because it's kind of a window to our origins on early Earth," Bishop says. "On our planet, life took off and we have plants and bacteria, we have highways and roads but on Mars you get to see the rocks, the planet isn’t contaminated by all the things we have here so you can see its history."
Mars may be a dry and desolate planet today, but scientists believe that it may have had a similar start to Earth, beginning as a warm and wet world. However, gradually over time, the planet lost its atmosphere.
"The evolution of the planet was kind of frozen in time, its not that it would’ve been the same as Earth but there could’ve been a lot of similarities," Bishop says.
WHAT'S NEXT — The new study suggests that the subsurface of Mars holds a lot more clues to the history and evolution of the planet than scientists previously believed.
Bishop suggests that more efforts need to be concentrated on drilling beneath the surface of Mars.
"So far, we've only seen the surface," Bishop says.
NASA's Mars rovers have poked at rocks, and the space agency's Insight mission, which has been attempting to drill on the Red Planet, recently called it quits. However, the upcoming European Space Agency's ExoMars mission, which is scheduled to launch in 2022, will dig two meters beneath the surface.
From there, Bishop hopes to get a better understanding of the processes that are taking place beneath the surface.
"Understanding the processes on Mars helps us understand what happened on Earth since our history was erased," she says.
Abstract: On Mars, seasonal martian flow features known as recurring slope lineae (RSL) are prevalent on sun-facing slopes and are associated with salts. On Earth, subsurface interactions of gypsum with chlorides and oxychlorine salts wreak havoc: instigating sinkholes, cave collapse, debris flows, and upheave. Here, we illustrate (i) the disruptive potential of sulfate-chloride reactions in laboratory soil crust experiments, (ii) the formation of thin films of mixed ice-liquid water “slush” at −40° to −20°C on salty Mars analog grains, (iii) how mixtures of sulfates and chlorine salts affect their solubilities in low-temperature environments, and (iv) how these salt brines could be contributing to RSL formation on Mars. Our results demonstrate that interactions of sulfates and chlorine salts in fine-grained soils on Mars could absorb water, expand, deliquesce, cause subsidence, form crusts, disrupt surfaces, and ultimately produce landslides after dust loading on these unstable surfaces.