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Mystery of 2 million black streaks on Mars may finally have been solved

Mars is a stripy planet with millions of black streaks that have puzzled scientists for decades — but now researchers may finally have found a proper explanation. So, what are they exactly? They were first found in the 1970s and researchers thought they were the evidence of landslides caused by melting ice. (Picture: ESA)
While the experts still think the streaks are the result of landslides, they believe these were ‘dry processes’ that do not involve any water. This narrowed down the list of potential causes, but did not settle the debate around the streaks’ origins. In one example, on Apollinaris Mons — an extinct shield volcano located just south of Mars’ equator — hundreds of parallel streaks can be seen on a single side of a large ridge. (Picture: Heritage Space/Heritage Images/Getty Images)
These streaks appeared between 2013 and 2017, and researchers later realised they were the result of a nearby meteoroid impact. So, experts concluded that meteoroid impacts and other seismic events, such as marsquakes, are responsible for most of the slope streaks. But a new study, in the journal Nature Communications, suggests that this is not the case. An analysis of  around 2.1 million slope streaks, pictured by Nasa’s Mars Reconnaissance Orbiter between 2006 and 2024, revealed almost all new streaks are the result of seasonal wind and dust erosion. (Picture: ESA)
Lead author Valentin Bickel from the University of Bern in Switzerland said: ‘Dust, wind and sand dynamics appear to be the main seasonal drivers of slope streak formation. Meteoroid impacts and quakes seem to be locally distinct, yet globally relatively insignificant drivers.’ Colin Wilson, ESA’s project scientist for the ExoMars Trace Gas Orbiter, said: ‘These observations could lead to a better understanding of what happens on Mars today. Obtaining long-term, continuous and global-scale observations that reveal a dynamic Mars is a key objective of present and future orbiters.’ (Picture: Nasa)
Dr Bickel’s analysis revealed slope streaks are grouped into five key regions across Mars. When new streaks form in each of these areas, it happens when seasonal wind speeds are highest and exceed the threshold for ‘dust mobilization.’ Then, when this threshold has been surpassed, landslides can more easily occur in that area. This process is similar to how high winds can pick up Martian dust. (Picture: Nasa)
So, why did it take so long for the researchers to figure this out? It seems that most of the activity happen under the cover of darkness. Dr Bickel said in the study: ‘The conditions most conducive to seasonal streak formation appear to occur at sunrise and sunset, explaining the lack of direct observations of streak-forming events to date.’ The study also revealed that slope streak formation likely occurs at an annual rate of around 0.05 new streaks per existing streak. Given that there are estimated to be 1.6 million slope streaks (as some streaks were included in multiple image sets) that means the current rate of formation is around 80,000 new streaks per year. (Picture: NASA/Arizona State University via Getty Images)
The slope streaks cover less than 0.1% of Mars’ surface. The new study suggests that they may be the largest single contributor to atmospheric dust. However, it is recommended that better understanding the streaks’ role in the Martian dust cycle could impact future human colonies on Mars and therefore should be a focus for future Mars missions. (Picture: Nasa)
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