A sweeping machine learning study scanning over 86,000 high-res Mars images reveals that the mysterious streaks seen on Martian slopes are likely dry dust slides, not evidence of flowing water as previously hoped.
Long debated as possible indicators of present-day water (and thus habitability), these streaks—some recurring seasonally—now appear to be more aligned with wind activity and dust movement.
Doubt Cast on Martian Water Flows
A surprising new study from scientists at Brown University and the University of Bern is shaking up what we thought we knew about Mars. For years, mysterious dark streaks have been spotted crawling down the Red Planet’s cliffs and crater walls. Some experts believed these streaks were caused by liquid water, raising hopes that Mars might still have habitable environments today.
But the latest research tells a different story. Using machine learning and one of the most comprehensive datasets ever created for Martian slope features, the researchers found no signs of water. Instead, they discovered strong evidence that the streaks are likely the result of dry processes, such as shifting dust and wind activity.
“A big focus of Mars research is understanding modern-day processes on Mars — including the possibility of liquid water on the surface,” said Adomas Valantinas, a postdoctoral researcher at Brown who coauthored the research with Valentin Bickel, a researcher at Bern. “Our study reviewed these features but found no evidence of water. Our model favors dry formation processes.”
The research was published today (May 19) in Nature Communications.
across Mars’ dusty surface in Arabia Terra. Credit: NASA
Streaks Spotted Since the Viking Mission
These strange streaks were first captured in the 1970s by NASA’s Viking mission. They appear darker than the surrounding terrain and stretch for hundreds of meters down steep slopes. Some of them stick around for years, while others seem to appear and vanish with the seasons.
The shorter-lived versions are called recurring slope lineae, or RSLs. These tend to show up in the same places during the warmest times of the Martian year. That seasonal pattern led many scientists to believe water might be involved, possibly from melting underground ice, salty brines, or moisture pulled from the air.
If that were true, these streaks could represent rare, life-friendly oases on an otherwise barren world.
Not Everyone Bought the Water Hypothesis
Not all researchers were convinced by the water explanation. Some believed these streaks might just look like flowing liquid when viewed from space. In reality, they argued, the features could be caused by completely dry activity, like small rockslides or powerful gusts of Martian wind.
Hoping for new insights, Bickel and Valantinas turned to a machine learning algorithm to catalog as many slope streaks as they could. After training their algorithm on confirmed slope streak sightings, they used it to scan more than 86,000 high-resolution satellite images. The result was a first-of-its-kind global Martian map of slope streaks containing more than 500,000 streak features.
“Once we had this global map, we could compare it to databases and catalogs of other things like temperature, wind speed, hydration, rock slide activity, and other factors,” Bickel said. “Then we could look for correlations over hundreds of thousands of cases to better understand the conditions under which these features form.”
Wind, Dust, and the Real Culprits
This geostatistical analysis showed that slope streaks and RSLs are not generally associated with factors that suggest a liquid or frost origin, such as a specific slope orientation, high surface temperature fluctuations or high humidity. Instead, the study found that both features are more likely to form in places with above average wind speed and dust deposition, factors that point to a dry origin.
The researchers conclude that the streaks most likely form when layers of fine dust suddenly slide off steep slopes. The specific triggers may vary. Slope streaks appear more common near recent impact craters, where shockwaves might shake loose surface dust. RSLs, meanwhile, are more often found in places where dust devils or rockfalls are frequent.
Implications for Future Mars Missions
Taken together, the results cast new doubt on slope streaks and RSLs as habitable environments.
That has significant implications for future Mars exploration. While habitable environments might sound like good exploration targets, NASA would rather keep its distance. Any Earthly microbes that may have hitched a ride on a spacecraft could contaminate habitable Martian environments, complicating the search for Mars-based life. This study suggests that the contamination risk at slope streak sites isn’t much of a concern.
“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.”
Reference: “Streaks on martian slopes are dry” by Valentin Tertius Bickel, and Adomas Valantinas, 19 May 2025, Nature Communications.
DOI: 10.1038/s41467-025-59395-w
Never miss a breakthrough: Join the SciTechDaily newsletter.
