Slope stripes are prominent dark markings on Martian slopes that naturally form and can fade over decades. Some planetary scientists interpreted these features as evidence of liquid flows, raising the possibility of a currently habitable environment on Mars. However, recent research by Brown and Bern Universities offers alternative explanations, focusing on drying processes associated with wind and dust activities.

“A significant focus of contemporary Mars research is understanding active processes on the planet, including the potential presence of liquid water on its surface,” states Dr. Admos Valantinus, a postdoctoral researcher at Brown University.

“In our study, we examined these features but found no evidence of water. Our model supports the idea of a dry formation process.”

The unusual stripes were first identified from images sent back by NASA’s Viking mission in the 1970s.

These stripes typically appear darker than the surrounding terrain, stretching across sloped regions that can extend several hundred meters.

While some stripes endure for years or decades, others appear and disappear more rapidly.

The phenomenon known as recurring slope features (RSLs) tends to manifest in the same locations during Mars’ warmest periods.

The origins of these stripes have fueled much debate among planetary scientists.

Seeking new insights, Dr. Valantinus and his colleague Dr. Valentin Bickel employed machine learning algorithms to catalog as many slope streaks as possible.

After training the algorithm on confirmed sightings of slope streaks, it was used to analyze over 86,000 high-resolution satellite images.

The outcome was the first comprehensive global map of slope streaks on Mars, featuring over 500,000 individual streaks.

“With this global map, we can compare it against a database of various factors such as temperature, wind speed, moisture, and rock slide activity,” said Dr. Bickel.

“This enables us to search for correlations across a vast number of cases to better comprehend the conditions under which these features form.”

This extensive analysis indicated that slope stripes and RSLs are generally not linked to conditions that would suggest the presence of liquid or frost, such as specific gradient directions, significant surface temperature fluctuations, or high humidity levels.

Instead, the authors posited that both features are likely to form in areas with moderate wind speeds and dust deposition, consistent with arid origins.

Researchers concluded that these stripes likely arise when fine layers of dust suddenly slide down steep slopes.

Variability in triggering factors was noted. Slope stripes are observed more frequently near recent impact craters where shock waves can disturb loose surface dust, while RSLs tend to be more prevalent in areas affected by dust devils and rockfalls.

Collectively, these findings raise new questions about the viability of slope stripes and RSLs as indicators of habitable environments.

This research holds significant implications for future Mars exploration efforts.

While a habitable environment may seem like an appealing exploration target, NASA aims to be cautious in this regard.

Earthly microorganisms potentially present on spacecraft could contaminate Mars’ habitable zones, complicating the search for extraterrestrial life.

This study suggests that the risk of contamination at slope streak locations is relatively low.

“This demonstrates the advantage of a big data approach,” noted Dr. Valantinas.

“It helps eliminate certain hypotheses from consideration before launching a spacecraft for exploration.”

The results were published on May 19, 2025, in Nature Communications.

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VT Bickel & A. Valantinas. 2025. The streaks on the slopes of Mars are dry. Nature Communications 16, 4315; doi:10.1038/s41467-025-59395-w