According to a study published in the journal Nature Geoscience, dark features earlier thought to be evidence of liquid water flowing on Mars may actually be granular flows comprising sand and dust.


The new findings indicate that the water-restricted conditions on Mars would make it difficult for Earth-like life to exist near the surface of the planet. The study is based on observations made with the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
Background
The researchers had discovered narrow, down-slope trending surface features called Recurring Slope Lineae (RSL) on Mars in 2011. The features were found to be darker than their surroundings.
The discovery gave rises to hopes of finding liquid water or brine on the otherwise dry planet.

About RSL Features
• The RSL features are known to grow incrementally, fade when inactive and recur annually during the warmest time of the year on Mars.
• They have mostly been discovered 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.
• The appearance and growth of these features resemble flowing liquid water. Their formation however, remains to be a mystery.
• The recent study demonstrated that the RSL flows seen by the Imaging Science Experiment camera are likely to be moving granular material such as sand and dust.
• The terminal end of the RSL slopes have been discovered to be identical to the slopes of sand dunes where movement is caused by dry granular flows.
The new understanding of the features supports other evidence that shows that Mars is very dry.