MORPHOLOGY AND DYNAMICS OF A MARTIAN SAND SHEET

Broad swaths of aeolian provinces on Mars and Earth have expansive and often fairly featureless sand sheets, though their detailed description and characterization scarcely appear in the literature. Understanding active sand sheets is needed to correctly interpret paleo-environments in strata and to understand the nature of what may be wind-drag ripples instead of grain-impact “reptation” ripples. Here we provide a first look at 25 km² of a rippled sand sheet located in Herschel Crater imaged by the high-resolution HiRISE camera in orbit around Mars and use derived digital elevation models and ripple displacement maps. We show that sand sheets’ ripples move more slowly with distance downwind but also move faster up local slopes, with speeds between 0.1-1 m/Earth year. While areally expansive, we find sand sheets are only 1-2 m high above the local bedrock, contrasted with up to 5 m for local dunes and 20 m for more regional dunes. If the large Martian ripples are wind-drag ripples as proposed by Lapotre et al. (2016), their behavior on sand sheets in the absence of dunes and terrestrial vegetation may constrain their formation and movement mechanisms. Furthermore, such a study may give insight into the mechanisms favoring sand sheet formation versus dune formation on Mars, such as the possible preponderance of grains too coarse for saltation but that can roll and bounce.