What Causes the Mysterious Slope Streaks on Mars?
In 1973, NASA’s Viking probes discovered slope streaks on Mars — discoveries that continue to fascinate scientists today. Some believe the streaks are caused by “wet” mechanisms, and others — by “dry” mechanisms, but ultimately, the exact causes remain unknown. The origin of streak formation, in the meantime, could have significant implications for future Mars missions.
A recent study from Sweden’s Luleå University of Technology, published in the American Geological Union’s Review of Geophysics, suggests that both mechanisms likely account for the slope streak formation, although wet mechanisms appear more prevalent. “We suggest that explanations considering both dry and wet processes can more holistically describe all the observed morphological variations among slope streaks,” the authors write. Wet mechanisms refer to transiently flowing liquid water on the surface of Mars, while dry mechanisms refer to dry dust avalanches.
The scientists reviewed literature that relies on technological improvements of the recent years, including high-resolution sensors and imaging capabilities. An improved understanding of seasonal cycles on Mars is also helping them take a fresh look at the existing data.
Proponents of the wet mechanism cite groundwater springs, melting surface ice, and salt solutions as potential causes. The dry mechanism theorists think the dust avalanches responsible for the slopes are caused by air fall deposits, subsurface melting, or disturbances such as rockfalls, meteorites or Marsquakes.
However, neither explanation is fully sufficient when it comes to the observed slope streaks. The wet mechanism theory is challenged by the lack of consistency with seasonal changes. If liquid water had indeed been the cause, the slopes would appear in areas with warmer seasonal temperatures. But that is not the case. Similarly, if the slope streaks are caused by dry mass displacements, as per the dry mechanism theory, scientists should be able to find evidence of the disturbances — such as a buildup of debris at the bottom of the slopes. That also hasn’t been found.
A recent study from Sweden compared the terrestrial formation in the Andean region Bolivia, which is analogous to that of Mars, and revealed that wet mechanisms seem to account for more of the slope formation and development. At the Salar de Uyuni site, the atmospheric and surface conditions are similar to those on equatorial Mars. Seasonal brine flows — in which chloride and sulphate salts become liquified — account for creating slope streaks in the region.
Study authors agree that more data is needed. “While available remote sensing data has vastly improved, as well as our knowledge of Martian mineralogy, climate, and atmosphere, we still need further investigations to advance our understanding. In this regard, targeting slope streak regions during future robotic or manned Mars missions would be advantageous,” they write.
While the origin of the slope streaks remains a mystery, scientists hope that with newer studies and advances in technology, they will be able to further study the subsurface mechanisms, specific seasonal changes and more. That kind of information about the surface of Mars is essential to future crewed missions — and even critical when contemplating habitability on the red planet.
Picture credit: NASA
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