When NASA announced the discovery of larger amounts of liquid water on Mars in 2015, hopes were significantly raised that we could one day soon find evidence of life on Earth's neighbour. However, exactly how these numerous flows begin and gradually grow has not yet been explained.
These features have evoked fascination and controversy since their 2011 discovery, as possible markers for unexpected liquid water or brine on an otherwise dry planet.
There are still unanswered questions, such as why the streaks appear and vanish with the seasons, and what makes them dark in color.
The scientists concluded that the range "matches that of slipfaces for active Martian and terrestrial dunes, interpreted as the range of critical angles for which granular flows of sand can terminate".
RSL are mostly found on steep rocky slopes in the dark regions of Mars, such as the southern mid-latitudes, Valles Marineris near the equator and in Acidalia Planitia on the northern plains.
But now, new research from scientists at the US Geological Survey suggests the markings were simply made by flowing sand and dust.
"This new understanding of RSL supports other evidence that shows that Mars today is very dry". The data include 3-D models of slope steepness using pairs of images for stereo information.
One of the reasons for the change is that scientists found that RSL were only visible on steep slopes. While the surface of Mars immediately boils water due to its low pressure, we thought water stored underground might be seeping to the surface.
Mars photos show an interesting landscape feature: dark streaks that appear to show flowing movement, which some thought may be water.
Working with the University of Arizona, Durham University and the Planetary Science Institute, the USGS researcher team has now identified these apparent signs of liquid as granular flows of sand and dust.