LAUSR

The first in situ investigation of an active dune field on another planetary surface occurred in 2015-2016 when the MSL Curiosity rover investigated the Bagnold Dunes on Mars. HIRISE images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra-annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity. Curiosity surface images show that limited changes nevertheless occurred, with movement of large grains, particularly on freshly exposed surfaces, two occurrences of secondary grain flow on the slip face of Namib Dune, and a slump on a freshly exposed surface of a large ripple. These changes are seen at sol-to-sol time scales. Grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0.3 - 0.4 m s-1. Overall, the correlation between changes and peak REMS winds is moderate, with high wind events associated with changes in some cases, but not in others, suggesting that other factors are also at work. The distribution of REMS 1 Hz wind speeds show a tail up to the 20 m s-1, showing that even higher speed winds occur. Non-aeolian triggering mechanisms are also possible. The low activity period at the dunes documented by Curiosity provides clues to processes that dominated in the Martian past under conditions of lower obliquity.