Seasonal Flows on Warm Martian Slopes

Short story: We have taken repeat images of dark flows at several sites on Mars using the Mars Reconnaissance Orbiter’s (MRO) High Resolution Imaging Science Experiment (HiRISE) camera. These features extend down slope from bedrock outcrops and appear to lengthen during warm seasons and fade in cold seasons. Flows recur over periods of months (to years) and are known as Recurring Slope Lineae (RSL). Individual lineae are narrow (0.5 to 5 meters) and form on steep equatorial-facing slopes (25 deg. to 40 deg.). These features are relatively rare in that they are found in only approximately 1% as many HiRISE images as are gullies. Liquid brines flowing out near the surface is presently the best hypothesis to explain their formation, although the exact mechanism and source of water are not yet understood.