STUDIES OF AEOLIAN BEDFORMS AND WIND ACTIVITY IN GALE CRATER FROM SURFACE TO ORBITAL SCALES

Gale Crater, currently being investigated by the Mars Science Laboratory (Curiosity), is unique among the 7 sites visited by landed spacecraft in that an active dune field (informally named the Bagnold Dunes) is along the rover traverse path. Orbital data from HiRISE show that the superposed ripples on the dunes move at rates of decimeters to meters per Earth year, with dune slip face advance at the decimeter scale. With Curiosity’s payload of high resolution imagers, data on terramechanics and surface properties, and the REMS meteorological package, the potential exists to correlate properties and changes at a full range of spatial scales from sand grains to dunes and tie to current wind conditions. REMS data show a repetitive pattern of upslope/downslope winds associated with thermal changes in air and surface temperature that are initiated after sunset and finish with sunrise. At the smallest scale, wind-induced changes are seen Curiosity images of drill tailings and dumped piles, with even ~millimeter-size grains being blown. At a larger scale, the MSL Team has been progressively taking images of the Bagnold dunes, with pixel scales now at sub-decimeter, exceeding HiRISE resolution. HiRISE has also been imaging the dunes about every six weeks to document any seasonal-induced wind changes. The Curiosity images show fine-scale ripple patterns not seen in the orbital data, although changes have not yet been documented. MSL has assessed sand shadows and ripples, with a common characteristic being a carapace of dust-encrusted coarse grains overlying a finer-grained and darker interior, consistent with stabilized bedforms investigated by the MER rovers. Some ripples show foresets indicative of cyclical or reverse flow. Correlation with HiRISE-derived albedo show that stabilized bedforms have brighter surfaces, with lower albedos found in the rippled surfaces within canyons north of the dunes, and the darkest surfaces in the Bagnold dunefield. Similarly, CRISM-derived spectral continuum slopes within the 0.7 to 2.4 microns wavelength range correlate to HiRISE-derived sand displacements, suggesting that less active sands are dustier. These integrated observations show that Gale Crater is an active aeolian environment, with the greatest changes seen on the dark dunes and disturbed areas.