Water on Mars? Mysterious Dark Streaks Aren't What Scientists Thought

Gizmodo

25-05-2025

Scientists have been arguing about the origin of strange streaks on Mars since the earliest missions to the Red Planet.
In 1976, NASA's Viking mission successfully landed the first spacecraft on Mars. When the mission began sending images from Mars' surface back to Earth, scientists noted long, dark streaks on crater walls and cliff sides. To this day, some researchers suggest that the strange geographical features are the result of water flow—but a recent study says otherwise.
Planetary scientists from Brown University and the University of Bern have used artificial intelligence to reveal that the enigmatic Martian streaks likely result from wind and dust, not water flow. Their results have important implications for future Mars exploration, as well as humanity's continuous search for habitable environments and life beyond Earth.
Some slope streaks are long-lasting, while others—called recurring slope lineae (RSL)—are more ephemeral, continuously appearing in the same places during Mars' hottest times of the year. Although Mars is generally dry and cold (with temperatures as low as -225 degrees Fahrenheit, or -153 degrees Celsius) small amounts of water from potential ice, underground sources, or humidity could conceivably mix with enough salt to become liquid and flow down a slope. Because water is a key ingredient for life on Earth, such formations might represent habitable regions on the Red Planet, too. But some researchers aren't convinced, arguing that dry processes could have created those features instead.
To settle the matter, the researchers trained an algorithm on a dataset of confirmed slope streak sightings, as detailed in a study published Monday in the journal Nature Communications. They then used the algorithm to scan over 86,000 high-resolution satellite images and compose a map of Martian slope streaks.
'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,' Valentin Bickel, co-author of the study and a University of Bern Center for Space and Habitability fellow, said in a Brown University statement. 'Then we could look for correlations over hundreds of thousands of cases to better understand the conditions under which these features form.'
Simply put, their results do not link slope streaks and RSLs with features indicating the presence of liquid or even frost. Instead, the researchers discovered that both slope streaks and RSLs tend to develop in areas with high wind speed and dust deposition. In other words, they are likely caused by a dry process in which dust layers abruptly slide down a slope, triggered by external forces.
Rather than seeing these results as yet another failure in our search for extraterrestrial life, the planetary scientists explain that the study still carries weight for future Mars explorations. If their research had confirmed the theory that slope streaks were caused by water, and that as a result the region might host some form of life, NASA would have actually avoided the area for the time being. That's because scientists fear that spacecraft and rovers might still harbor terrestrial life, such as microbes, which could contaminate Martian habitats and interfere with our search for Martian life.
'That's the advantage of this big data approach,' explained Adomas Valantinas, the other co-author of the study and a planetary scientist at Brown University who specializes in Martian geology. 'It helps us to rule out some hypotheses from orbit before we send spacecraft to explore.'
In an industry that seems obsessed with finding water on Mars, the study stands as a reminder that not every scientific breakthrough needs to be about extraterrestrial life.