A Martian mystery decades in the making might finally be solved!
The streaky slopes spotted on Mars since the 1970s—once suspected to be signs of salty water and potential habitability—are now thought to be the result of dry dust avalanches triggered by wind, impacts, or shifting rocks.
Mysterious Streaks on Olympus Mons
Strange dark and light streaks cover the slopes near Olympus Mons, the largest volcano on Mars. These marks were captured in stunning detail by a camera called CaSSIS, onboard the European Space Agency’s ExoMars Trace Gas Orbiter.
For decades, scientists have been captivated by these sweeping patterns that look as if someone dragged a giant broom across the Martian surface.
What makes these streaks even more mysterious is how they appear and disappear without warning. Some fade within months, while others linger for years. They change brightness and color with the seasons and show up on slopes in both hemispheres of the Red Planet.
First Glimpses from the Viking Era
The first images of these streaks were captured by NASA’s Viking orbiters in the 1970s. They revealed long, narrow marks stretching hundreds of meters down sloped terrain. Since then, scientists have debated what causes them and whether they could be linked to water and possibly life.
One long-standing theory suggested they were created by flows of salty water, or brine. If true, it would mean that small pockets of potentially habitable environments might exist on Mars, even in its freezing conditions.
But now, a new study from researchers at the University of Bern and Brown University offers a different explanation. Published in Nature Communications, the research suggests these streaks aren’t caused by water at all.
Instead, the scientists believe they are the result of dry processes involving wind and dust. Rather than briny flows, it may be Martian dust sliding downhill that creates these eye-catching patterns.
across Mars’ dusty surface in Arabia Terra. Credit: NASA
Half a Million Streaks Mapped
Researchers turned to a machine learning algorithm to scan and catalog slope streaks in over 86,000 satellite images from NASA’s Mars Reconnaissance Orbiter (MRO).
Scientists combined several decades’ worth of orbital data and the neural power of deep learning to produce a global map with almost 500,000 streak features across Mars. The new study created the largest database yet of these features on Mars.
Orbiters Reveal Evolving Patterns
The team also turned to other cameras orbiting Mars, such as the CaSSIS imager on ESA’s Trace Gas Orbiter and MRO’s HiRISE, to collect more color information in high resolution, as well as to monitor how the streaks evolved over time.
The correlations over hundreds of thousands of cases helped the team shed new light on a decades-old debate. With no evidence of water, scientists concluded that dry processes, rather than liquid flow, drive the appearance of streaked slopes on Mars.
Dust, Wind, and Impacts
The study found that these winding features most likely form when layers of fine dust suddenly slide off steep terrain. Multiple triggers could unleash this process, such as rocks falling, small meteoroid impacts, or wind gusts causing shockwaves and shaking loose dust.
To bring out these features, the contrast in these CaSSIS images is stretched – the image is rescaled between the minimum and maximum brightness within each color before combining them to produce the published image.
Ongoing Exploration with ExoMars
ESA’s ExoMars Trace Gas Orbiter continues to image Mars from orbit to understand its ancient past and potential habitability. The spacecraft returns spectacular images and provides the best inventory of atmospheric gases, and mapping the planet’s surface for water-rich locations.
Understanding the history of water on Mars and whether it once allowed life to flourish is at the heart of ESA’s ExoMars missions.
Explore Further: NASA’s Mars Streak Mystery Might Finally Be Solved
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
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4 Comments
The ‘dust’ explanation doesn’t explain the darkening of the streaks. Generally speaking, dry silicates get lighter in tone as the particle size is reduced, and coarser particles are less easily moved by wind.
Another problem, which I remarked about in the May 20th SciTechDaily story, is that the streaks seem to originate from point sources, and there is difficulty explaining the volume of ‘dust’ spread out down-slope from a point source, UNLESS it is from groundwater coming up at an intermittent spring.
You should read the research paper. It partially supports your hypothesis, but also explains why it’s unlikely that these streaks are formed by water due to the population density and the time of year when they’re formed.
The peak season for streak formation occurs during conditions in which liquid water is unlikely due to temperature. As for the dark versus bright streaks, the bright streaks seem to be older streaks which have been faded, the darker streaks seem to be younger streaks and have a high and seem to coincide with newer impact sites.
Lastly, the high contrast of the images that were published were intentionally adjusted to make the features more apparent.
I do usually read the linked, original research papers. However, I have been preoccupied with preparing for a talk that I gave last night. Now that is done, I have a little more free time and I read it today. Thank you for the suggestion.
I’m generally leery of models because of the (usually unstated) assumptions in the models. Without field validation, which is difficult for Mars, one doesn’t know whether the models are reliable or not. With a long history of working in the remote sensing field (>25 years), I know from personal experience that different types of multispectral thematic classifiers will give different results. Working for the City of Scottsdale (AZ) on a NASA grant, I discovered that most of the software classifiers were fooled by creosote patches in the Sonora Desert because of the dark shadows, confusing the permeable, shadowed areas with impermeable, sun-lit asphalt streets and parking lots. It takes a human to interpret the context to realize the classifier made a mistake. However, even a human selecting spectral training sites can bias the results and result in obviously incorrect classifications. AI is not without its problems. Being a remote sensing scientist, with a classification algorithm patent in my name, I have more than a passing acquaintance with contrast stretching of imagery.
You said, “The peak season for streak formation occurs during conditions in which liquid water is unlikely due to temperature.” On the contrary. The original, linked article you suggested I read says, “Bright and dark streaks feature a STRONG correlation between estimated size,…, MCD (Mars Climate Database) diurnal surface temperature amplitude, albedo, and nanophase ferric iron: larger streaks appear to feature lower MOLA elevation and HIGHER diurnal temperature amplitude, albedo, and nanophase ferric iron values.” On Earth, strong sunlight, even in the middle of Winter, can result in melting of ice on sidewalks and asphalt pavements.
You also claimed, “… the bright streaks seem to be older streaks which have been faded, …” That is not inconsistent with brines wetting and darkening regolith, and then either draining away or evaporating, particularly if the evaporation leaves a coating of white crystals on the regolith particles.
Still, I’m most uncomfortable with the large volume of streaks emanating from a point source. The authors don’t really address the issue other than supplying estimates of the volume, which really weakens their conclusions, in my opinion.
Could these be sulfur vents with chloro hydrates? Or perhaps other hot rocks off gassing? Seems unlikely. Second guess would be a funnel tunnel. Ie dust channeled into a geographical formation acting like a funnel then uplifting them at the end of the channel where the wind could transport them great distances? Third guess, a geographical formation which creates a dust devil when the wind is from a certain direction?