Some experts believed these streaks were caused by liquid water, raising hopes that Mars might still have habitable environments today.
Using machine learning and one of the most comprehensive datasets ever created for Martian slope features, the researchers found no signs of water.
Hoping for new insights, Bickel and Valantinas turned to a machine learning algorithm to catalog as many slope streaks as they could.
The result was a first-of-its-kind global Martian map of slope streaks containing more than 500,000 streak features.
Implications for Future Mars Missions Taken together, the results cast new doubt on slope streaks and RSLs as habitable environments.
The mysterious streaks observed on Martian slopes are probably dry dust slides rather than the hoped-for indication of flowing water, according to a comprehensive machine learning study that scanned over 86,000 high-resolution Mars images.
Previously disputed as potential markers of current water (and hence habitability), these streaks, some of which occur seasonally, now seem to be more consistent with dust movement and wind activity.
The Martian water flows are questioned.
A startling new study by researchers from the University of Bern and Brown University is upending our preconceived notions about Mars. For many years, people have noticed enigmatic dark lines creeping down the crater walls and cliffs of the Red Planet. It was thought by some experts that liquid water was the cause of these streaks, which gave rise to the possibility that Mars still has habitable environments today.
However, recent studies provide a different picture. The researchers discovered no evidence of water using machine learning and one of the most extensive datasets ever produced for Martian slope features. Rather, they found compelling evidence that dry processes like wind activity and shifting dust are probably responsible for the streaks.
Understanding current processes on Mars, such as the potential for liquid water on the surface, is a major focus of Mars research, according to Adomas Valantinas, a postdoctoral researcher at Brown who coauthored the study with Valentin Bickel, a researcher at Bern. “We examined these features in our study, but we couldn’t find any indications of water. We favor dry formation processes in our model. “.”.
Today, May 19, the study was released in the journal Nature Communications.
Remarkable occurrences since the Viking Mission.
The Viking mission of NASA first observed these odd streaks in the 1970s. They stretch for hundreds of meters down steep slopes and appear darker than the surrounding terrain. While some seem to come and go with the seasons, others remain for years.
Recurrent slope lineae, or RSLs, are the shorter-lived types. During the warmest months of the Martian year, these typically appear in the same locations. Many scientists thought that water might be involved because of that seasonal pattern, either from moisture drawn from the air, salty brines, or melting subterranean ice.
If that’s the case, these streaks might be one of the few oases of life on an otherwise arid planet.
The Water Hypothesis Didn’t Win Over Everyone.
Not every researcher agreed with the water explanation. Some thought that when seen from space, these streaks might simply appear to be flowing liquid. In actuality, they contended, the features might have been brought about by entirely dry activity, such as fierce Martian wind gusts or tiny rockslides.
A machine learning algorithm was used by Bickel and Valantinas to catalog as many slope streaks as possible in the hopes of gaining new information. They scanned over 86,000 high-resolution satellite photos using their algorithm, which they had trained on verified slope streak sightings. A unique global Martian map of slope streaks with over 500,000 streak features was the end result.
Bickel stated, “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.”. Then, in order to gain a better understanding of the circumstances in which these features form, we could search for correlations across hundreds of thousands of cases. “.”.
Dust, Wind, and the True Accusers.
This geostatistical analysis demonstrated that slope streaks and RSLs are typically not linked to characteristics like a particular slope orientation, high surface temperature fluctuations, or high humidity that would indicate a liquid or frost origin. Rather, the study discovered that both features are more likely to form in locations with above-average wind speeds and dust deposition, which are indicators of a dry origin.
The streaks are most likely the result of fine dust layers abruptly sliding off steep slopes, the researchers conclude. The particular triggers can change. Near recent impact craters, where shockwaves may shake loose surface dust, slope streaks seem more prevalent. Conversely, RSLs are more common in areas with frequent rockfalls or dust devils.
Implications for Upcoming Mars Expeditions.
Together, the findings raise fresh questions about slope streaks and RSLs’ suitability as livable places.
For upcoming Mars exploration, that has important ramifications. NASA would prefer to stay out of the way, even though habitable environments might seem like good exploration targets. The search for life on Mars could become more difficult if any Earthly microbes that might have traveled with a spacecraft contaminate environments that are habitable on Mars. According to this study, there isn’t much of a risk of contamination at slope streak locations.
“This big data approach has that advantage,” Valantinas stated. “It assists us in eliminating certain theories from orbit prior to deploying spacecraft for exploration. “.”.
Reference: Valentin Tertius Bickel and Adomas Valantinas, “Streaks on Martian slopes are dry,” Nature Communications, May 19, 2025.
Reference: 10.1038/s41467-025-59395-w.
