Mysterious dark streaks first observed on Mars in the 1970s are not what many believed they were.
Scientists now say the curious features that stretch for hundreds of meters down Martian slopes were likely signs of wind and dust activity — not water.
“A big focus of Mars research is understanding modern-day processes on Mars — including the possibility of liquid water on the surface,” Adomas Valantinas, a postdoctoral researcher at Brown University, said in a statement. “Our study reviewed these features but found no evidence of water. Our model favors dry formation processes.”
Valantinas and the University of Bern’s Valentin Bickel coauthored the research which was recently published in the journal Nature Communications.
To reach these conclusions, the researchers used a machine learning algorithm to catalog as many of the odd streaks as they could, creating a first-of-its-kind- global Martian map containing some 500,000 from more than 86,000 high-resolution images from NASA’s Mars Reconnaissance Orbiter.
Then, they compared their map to databases and catalogs of other factors, including temperature, wind speed, hydration, and rock slide activity. They looked for any correlations over hundreds of thousands of cases.
The authors found that the ominous streaks that don’t last for decades, known as recurring slope lineae or RSLs, are not generally associated with factors that suggest a liquid or frost origin. Those factors might include a specific slope orientation, high surface temperature fluctuations, and high humidity. The features were more likely to form in places with above-average wind speed and dust deposition. That points to a dry origin of formation, and they seem to show up in the same locations during the warmest periods of the Martian year before mysteriously vanishing.
They concluded that the older slope streaks, which run down cliff faces and crater walls, most likely form when dust suddenly slides off slopes following seismic activity, winds, or even the shockwaves from meteoroid impacts. The streaks appear most often near recent impact craters, where shockwaves may shake the surface dust loose. The shorter-lived ones are typically found in places where dust devils or rockfalls are frequent.
“There were statistically significant correlations between new impact sites and the appearance of nearby slope streaks in certain regions, supporting this view,” NASA said.
Previously, some had interpreted those streaks as liquid flows. It’s possible that small amounts of water could mix with enough salt to create a flow on the frozen Martian surface, Brown University noted. The red planet was once more temperate, and there is water under the surface of Mars. Others believed they were triggered by dry process. These results cast new doubt on slope streaks and RSLs as habitable environments.
“That’s the advantage of this big data approach,” Valantinas said. “It helps us to rule out some hypotheses from orbit before we send spacecraft to explore.”
