On Mars, strange dark streaks streak the slopes of volcanoes and craters. Spotted in the 1970s, these marks have long been interpreted as traces of flows linked to the presence of water. But despite decades of orbital observations, their exact origin remained uncertain. A team of researchers from the Center for Space and Habitability at the University of Bern, in Switzerland, now offers a rigorous explanation, based on the geostatistical analysis of more than two million streaks.
Published in Nature Communications on November 6, 2025, the study led by Valentin Bickel challenges long-dominant hypotheses by demonstrating that these marks result almost exclusively from dry processes linked to wind, sand and dust. A paradigm shift that sheds light on the current climate dynamics of Mars and refines the priorities of future exploration missions.
A massive inventory thanks to artificial intelligence
To finally understand the dark streaks on Mars, Valentin Bickel analyzed more than 91,000 images taken between 2006 and 2024 by the CTX camera on board NASA's Mars Reconnaissance Orbiter (MRO). Its objective: to identify, quantify and locate these mysterious marks. To achieve this, it trained a machine learning algorithm based on the YOLOv5 architecture. It is a visual detection system used in computer vision.
This tool made it possible to detect 2.1 million dark streaks on Martian slopes. Of which approximately 1.6 million are unique once duplicates are removed. Each streak is a dark mark of approximately 0.1 km² on average, which generally persists for several decades. The data reveals that these streaks are not uniformly distributed across the planet's surface. They are concentrated in five major geographic regions: Amazonis, Arabia, Tharsis, Elysium and the Olympus Mons halo (OMA). This distribution corresponds to areas where there are steep slopes covered with fine dust.
The method achieved 94% accuracy in recognizing streaks, with a recall rate of 75%. This means that the algorithm missed about a quarter of the existing streaks, but produced very few false positives. This massive census represents the most robust scientific base ever established on this phenomenon. It thus opened the way to a global, spatiotemporal and mechanistic understanding of the role of these marks in the current dynamics of the red planet.
Training dictated by winds and dust
Old hypotheses favoring aqueous flows. However, the new data indicate formation mainly by dry dust slides, triggered by the wind. According to Valentin Bickel, these slides occur when atmospheric conditions reach a wind stress threshold greater than 0.02 pascal. It represents a critical value identified as sufficient to initiate the lifting of grains of sand (so-called phenomenon of saltation).
Once set in motion, these grains of sand, approximately 100 micrometers in size, strike the surface. They then dislodge finer dust particles, causing them to slide down slopes. This mechanism can be compared to that of avalanches, but without water or ice. The activity is highly seasonal. The data reveals that most streaks appear between solar longitudes 220° and 360°. They correspond to Martian southern spring and summer. During this period, the wind increases, and the quantities of dust in the atmosphere are also higher.
The regions where these streaks form are characterized by surfaces with high albedo (greater than 0.26). A sign of heavy dust deposition. But also regions with relatively low altitudes, between –2000 and –2500 meters. Cross-referencing imaging data and Martian atmospheric models also shows that nearly 60% of streaked areas regularly experience winds strong enough to trigger this process, which confirms their dominant role.
Finally, the simulations reveal that ideal training conditions often occur at sunrise or sunset. Which could explain why no streak formation has yet been observed live by the orbiters. Indeed, they mainly imaged in the middle of the day.
Exceptional causes: earthquakes and meteorite impacts
If wind and dust remain the main driving forces, certain streaks also form in reaction to sudden events such as meteorite impacts or Martian earthquakes. However, these phenomena remain extremely marginal, explains Bickel in the press release. According to the analysis, less than 0.1% of the streaks identified come from impacts or tremors on Mars.
Between 2006 and 2020, only 14 cases out of 254 confirmed impact zones showed the formation of streaks following a collision. The most emblematic example is that of Apollinaris Mons. Around a hundred parallel streaks appeared between 2013 and 2017 following an impact identified on images from the CaSSIS camera of the ExoMars Trace Gas Orbiter (ESA) mission. This type of event, well documented, has allowed us to better understand the localized triggering mechanisms.
As for earthquakes, data from the InSight mission, which recorded tremors between 2018 and 2022, indicate a possible correlation for only two seismic events with the appearance of streaks. Namely: S0105a and S0173a, with respective magnitudes of 3.0 and 3.7. The formation of 10 to 15 new streaks followed these events in the estimated epicenter regions.
The weakness of this correlation does not allow us to completely exclude their role. Especially since observations still remain limited in time and space. But for Bickel, even in these cases, “ the overall impact on the formation of streaks remains negligible “. Impacts and earthquakes therefore seem to act as punctual triggers, causing local “surges”. But they in no way constitute a regular or dominant driver of the phenomenon on a planetary scale.
An underestimated role in the current Martian climate
If they only cover a tiny portion of the Martian surface — about 0.1% — the dark streaks could have a disproportionate impact on the atmosphere. Indeed, their formation involves the movement of large quantities of dust. A significant part of which would be released into the air. Based on the average dimensions of the streaks and an estimated thickness of 5 centimeters, Bickel estimates that their annual formation is equivalent to the release of approximately 760 million tons of dust into the atmosphere. That is the equivalent of nearly two Martian planetary storms per year.
This figure suggests that streaks may represent the main natural contributor to the dust enrichment of Mars' atmosphere. Even in the face of local storms and dust devils (dust devils). However, Martian dust plays a central role in the planet's climate, affecting the temperature, wind circulation, and transparency of the atmosphere. During some extreme events, such as the 2001 global storm, visibility dropped to almost zero within a few days.
Understanding the operation and impact of streaks therefore becomes crucial for robotic missions and future manned missions. Excess dust can, for example, damage solar panels, limit communications or modify the conditions for lowering a machine. Additionally, the seasonal regularity of the streaks could serve as an indicator of current atmospheric activity. In addition to direct meteorological observations.
Finally, the research invites us to rethink the place of processes
dry in the recent evolution of the Martian surface. This type of process, often neglected in favor of aqueous or glacial scenarios, could in reality constitute a major player in the current shaping of the Martian landscape.
Source: Bickel, V. T. “Dust, sand and wind drive slope streaks on Mars”. Nat Common 169583 (2025).
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