Leonard David's INSIDE OUTER SPACE

Bright and dark streaks covering the slopes of the Olympus Mons aureole as seen by the European Space Agency’s ExoMars Trace Gas Orbiter using its Color and Stereo Surface Imaging System (CaSSIS). The image covers an area of approximately 50 square kilometers and was captured on October 3, 2024.
Image credit: ESA

Bright and dark streaks on Mars have sparked decades of debate.

Some experts interpret them as streaks, also cataloged as recurring slope lineae (RSL), created by flows of salty water, or brine, that could remain liquid long enough to form them. If so, perhaps they offer rare habitable zones on the Red Planet, a world where temperatures rarely rise above freezing.     

But a new study led by planetary scientists at the University of Bern and Brown University throws cold water – nope, better to say — dry processes involving wind and dust activity!

On patrol – NASA’s Mars Reconnaissance Orbiter (MRO).
Image credit: NASA/JPL

Evolving over time

Researchers used a machine learning algorithm to scan and catalogue slope streaks in over 86,000 satellite images taken by NASA’s Mars Reconnaissance Orbiter (MRO). The team also turned to other cameras orbiting Mars by the European Space Agency’s Trace Gas Orbiter as well as MRO’s super-powerful High Resolution Imaging Science Experiment.

That Mars-orbiting gear has helped monitor how the streaks evolved over time.

Multiple triggering events

Writing in a just-issued research paper, the scientists concluded that dry processes – rather than liquid flow – drive the appearance of streaked slopes on Mars. They found that these winding features most likely form when layers of fine dust suddenly slide off steep terrain.

Global distribution of slope streaks and RSL on Mars.
Image credit: Valentin Tertius Bickel/Adomas Valantinas

There are multiple triggering events that could unleash this process, such as rocks falling, small meteoroid impacts or wind gusts causing shockwaves and shaking loose dust.

Dry drivers

“Overall, our observations suggest that slope streak and RSL formation may be predominantly controlled by two independent, dry drivers,” the paper explains: 1) the seasonal delivery of dust onto topographic inclines, and 2) the spontaneous activation of accumulated dust by energetic triggers – wind and impacts for slope streaks, as well as dust devils and rockfalls for RSL.

“This implies that slope streak and RSL locations are not likely to be habitable, alleviating strict planetary protection measures for future landed missions to those regions,” the research paper concludes.

For more details, take a look at “Streaks on martian slopes are dry” in Nature Communications at:

https://www.nature.com/articles/s41467-025-59395-w

Visualization of the deep learning-driven mapping workflow.
Image credit: Valentin Tertius Bickel/Adomas Valantinas