Dark features earlier proposed as evidence of liquid water flowing on Mars may actually be granular flows, where sand and dust move rather than liquid water. The new findings, published in the journal Nature Geoscience, indicate that the water-restricted conditions that exist on Mars would make it difficult for Earth-like life to exist near the surface of the planet.
The researchers analysed narrow, down-slope trending surface features on Mars that are darker than their surroundings, called Recurring Slope Lineae, or RSL. 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.
The appearance and growth of these features resemble seeping liquid water, but how they form remains unclear, and this research demonstrated that the RSL flows seen by HiRISE are likely moving granular material like sand and dust. Water almost certainly is not responsible for this behaviour, which would require the volume of liquid to correspond to the length of slope available, producing more liquid on longer slopes