The NASA Curiosity Rover has shown us evidence of ancient rivers and bodies of liquid water on the martian surface. Given it's thin cold atmosphere, seeps of liquid water, presently on the surface of Mars which are capable of hosting microbial life appear to be unlikely. Scientists were thus surprised when high resolution imaging of the red planet's surface revealed thousands of intriguing dark streaks called RSL on hundreds of rocky slope areas. These fascinating features slowly extend down hill and grow during the martian warm season, fade during the colder season, and reappear during the next martian warm period. On Earth features like these are produced by seeps of liquid water. However, on Mars a careful study of 151 RSL features at ten different sites using the high resolution camera on NASA's Mars Reconnaissance Orbiter reveal that they occur almost entirely on slopes which are greater than 27 degrees. This new research published in Nature Geoscience suggests that RSL are composed of solid particles in dry granular flows which unlike water seeps appear to end on many of the dunes when it's slope falls below a critical value. What makes RSL tick remains a mystery and likely involves small amounts of water trapped from the atmosphere. Currently surface conditions are hostile to life as we know it, however, the possibility of finding evidence of ancient life or perhaps even still existing microbe colonies in deep sub surface pockets of water are reasons to continue to explore our next door neighbor without contaminating it.

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