Hopes for flowing water on Mars appear dashed after recent work from Brown University and the University of Bern in Switzerland examined the cause behind mysterious markings on the red planet‘s surface.
From the heights of Martian cliffsides and crater walls, unexplained streaks appear, with the possible flow of water put forward as one possible explanation for these intriguing markings on the Red Planet.
If true, such assertions would indicate that Mars was potentially habitable in the remote past, and possibly even today. So, what do scientists from Brown and Bern now believe is really happening?
Viking Observations and Mysterious Marks
In 1976, NASA’s Viking mission orbited Mars, collecting imagery and eventually landing on the surface. Those early images provided scientists with their first look at the mysterious markings, which stretch for hundreds of meters down Martian slopes. Most intriguingly, the streaks are not permanent. While some persist for decades, others vanish in less than a year. A correlation to surface temperature has also been observed, as recurring slope lineae (RSL) often reappear in the same areas as Mars warms.
Although the marks visually resemble flowing water, many researchers contest that interpretation, highlighting the extreme difficulty of sustaining surface water on Mars. The planet is a frozen desert, with temperatures that rarely rise above freezing. Given these conditions, many suggest the water-like appearance is merely an illusion, more likely caused by wind, dust, or falling rocks.
Still, some scientists note that a narrow window of possibility remains. Subsurface aquifers or humid air might release trace amounts of liquid water, especially if mixed with salt to lower its freezing point. In this scenario, thawed surface ice could join the flow, raising the tantalizing possibility that RSLs point to habitable environments on modern Mars.
Exploring a Phenomenon
Researchers Valentin Tertius Bickel from the University of Bern and Adomas Valantinas from Brown University teamed up to investigate the long-running Martian mystery. They first trained a machine learning algorithm using known images of streaks and RSLs. Once calibrated, the algorithm was applied to an expansive dataset of 86,000 satellite images, identifying over 500,000 streaks. From this, the team produced the first global map of the phenomenon.
“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,” Bickel said. “Then we could look for correlations over hundreds of thousands of cases to better understand the conditions under which these features form.”
A Dry Suggestion
Dampening hopes for habitable Martian environments, the team’s analysis found that none of the factors typically associated with water—such as temperature changes, frost, or humidity—showed a significant correlation with RSL locations. Instead, the researchers discovered that wind speed and dust disposition were the most consistent contributing factors.
Bickel and Valantinas propose that the streaks are likely created by layers of fine dust suddenly displaced from steep slopes, leaving behind the streak-like patterns. The exact cause may differ from case to case: one-time streaks tend to coincide with impact craters, while areas prone to frequent rockfalls are more likely to produce recurring RSLs.
While the idea of Martian habitats teeming with microbial life is exciting, their absence actually simplifies exploration for future astronauts. Earth microbes accidentally transported to Mars could contaminate fragile extraterrestrial ecosystems. In the absence of such environments, NASA faces fewer ethical and biological concerns in exploring these streaks up close.
“That’s the advantage of this big data approach,” Valantinas said. “It helps us to rule out some hypotheses from orbit before we send spacecraft to explore.”
The paper “Streaks on Martian Slopes are Dry” appeared on May 19, 2025, in Nature Communications.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.