COMPARISON OF TRANSVERSE AEOLIAN RIDGES ON MARS TO RIPPLES AND DUNES ON EARTH

Transverse Aeolian Ridges (TARs) is a non-genetic term applied to wind-emplaced bedforms observed on Mars. For features with wavelengths less than about 100 meters, TARs on Mars may be the product of either ripple-related or dune-related emplacement processes. The Mars Exploration Rovers have documented the presence of granule ripples (sand-cored features coated with essentially a mono-layer of granules, particles typically 1 to 2 mm in diameter) at both of their landing sites. However, orbital images, including the fantastic new products currently being obtained by the High Resolution Imaging Science Experiment (HiRISE), are not able to resolve the size of particles that comprise aeolian bedforms on Mars. We have collected detailed topographic profiles across aeolian bedforms ranging from typical sand ripples (wavelength of about 10 cm) to granule ripples (generally wavelengths of 1 to 5 m) to transverse sand dunes, both active and stabilized (wavelengths generally greater than 50 m), which comprises a rich data set to which measurements of TARs can be compared. This report presents some of our first results of photoclinometrically derived topographic profiles across TARs that are present in the first full-resolution HiRISE image released to the public, covering a portion of the floor of Ius Chasma within the immense Valles Marineris canyon system. The TAR profiles are generally steeper in slope and more symmetric (relative to the crest) than the terrestrial bedform profiles. TAR shapes are more divergent from the shapes of both sand ripples and sand dunes than they are from the shape of granule ripples. We are convinced that TAR profiles from HiRISE images can provide a valuable tool for assessing the probable formation mechanism of aeolian bedforms in the 10 to 100 meter wavelength range from regions all across Mars.