GLOBAL DATABASE OF AEOLIAN BEDFORM ACTIVITY ON MARS

The multiple dune fields and sand sheets observed on Mars attest to the importance of wind-driven (aeolian) activity in shaping the surface. Change detection analyses, using multi-temporal images (as fine as 0.25 m/pixel) acquired by the High Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter, can now be used to assess aeolian bedforms for evidence of activity over multiple Mars years. Results reveal present-day movement of sand by the wind and migration of bedforms (dunes and ripples) in some locations in the current climate and ~6 mbar atmosphere, and no apparent changes or movement in other locations. We present a database of >150 globally distributed dune fields and sand sheets with results from change detection analyses of HiRISE images separated in time by 1 or more martian years. The dataset includes dune morphologies of barchan, barchanoid, transverse, linear, dome, and star dunes; bedform classes include large dunes, and meter-scale ripples superposing dunes or superposing surrounding sand patches, aprons, and sand sheets. Migration rates are averaged over the time lapse between repeat imaging and are reported where bedforms are migrating. Upper limit migration rates are reported for bedforms not yet showing migration and are calculated using the image resolution and the time interval between repeat images. Average dune and ripple migration rates are ~0.5 m/Earth yr (1σ ±0.4 m/Earth yr), although collective ripple rates for a given dune are greater than for the dune they are superposed on. We will report on the characteristics of the dune fields and their surrounding environment in relation to their activity (e.g., crater vs. plains, elevation, presence of topographic features). Most striking is the contrast between the activity of dunes in the north and south polar regions. In the north, bedforms exhibit high annual migration rates despite limited frost-free time to be active, while southern bedforms decrease in activity with dunes showing no detectable migration at latitudes >57°S. These differences are attributed to strong katabatic and anabatic winds associated with the high elevation north polar cap compounded by the influence of seasonal volatiles, along with the longer and colder winters and higher average elevation (lower surface pressure) in south polar areas.