NON-TRANSVERSE WIND RIPPLE MIGRATION IN THE MARS SCIENCE LABORATORY LANDING SITE IN GALE CRATER (MARS)

Wind ripples represent the smallest features in the hierarchical system of aeolian bedforms consisting of ripples, dunes and draas. Their movement is related to the processes of saltation and reptation and their... [ view full abstract ]

Wind ripples represent the smallest features in the hierarchical system of aeolian bedforms consisting of ripples, dunes and draas. Their movement is related to the processes of saltation and reptation and their characteristics (wavelength and amplitude) are modulated by the grain size, wind speed, and roughness height. On Earth, where winds above the threshold for sand movement frequently occur at the surface, patterns of wind ripples can rapidly change in response to a variation in the wind direction, and ripple crestlines tend to quickly orient transversely to the last sand-moving wind. Exceptions are represented by ripples evolving on high sloping surfaces (e.g. dune flanks) where gravity enhances along-crest transport and ripples forming in a bi-directional wind regime when the angle between the two winds is obtuse. Longitudinal and oblique wind ripples have been obtained experimentally, but never observed in the field. Because aeolian ripples provide an instantaneous indication of the local wind regime they have been widely used to constrain wind conditions on Mars where direct measures of the winds at the surface are scarce. In addition, ripple migration rates have been used to constraints important parameters for landscape modification on Mars such as sand fluxes and erosion rates. In this report we show evidence for non-transverse wind ripple migration in the NASA Mars Science Laboratory (MSL) landing site in Gale Crater on Mars by using a set of multi-temporal high resolution orbital images. Two classes of ripples, straight and sinuous, are observed to evolve longitudinally with minimal lateral migration. As far as we are concerned, this represents the first field evidence for longitudinal ripple migration and suggests that the assumption of the transverse nature of wind ripples must be used with caution on Mars. In addition, we refine previous ripple and dune migrations estimates along the MSL Curiosity's traverse by using a manual and an automatic approach. Collectively, our findings show that the MSL landing site in an active environment, with the action of the wind being a major agent of landscape modification in the current atmospheric setting. Roving between the dunes represents a unique opportunity to validate the accuracy of wind predictions and to make the first ground observations of longitudinal ripples on Mars.