Transverse Aeolian Ridges on Mars: First results from HiRISE images

Three images obtained by the High Resolution Imaging Science Experiment (HiRISE) were analyzed for the information they could provide regarding Transverse Aeolian Ridges (TARs) on Mars. TARs from five locations in a HiRISE image of the floor of Ius Chasma show remarkably symmetric (cross-sectional) profiles, with average slopes for the entire feature of ~ 15°; these results apply to TARs that span an order of magnitude in wavelength and a factor of 6 in height. A HiRISE image of Gamboa impact crater in the northern lowlands shows low albedo sand patches < 2 m high that are covered with sand ripples, surrounded by larger TAR-like ripples that are very similar in profile to surveyed granule ripples on Earth. TARs in a HiRISE image from Terra Sirenum, in the cratered southern highlands, are comparable in height to those in Ius Chasma, but many have tapered extensions that are more consistent with them being erosional remnants rather than the result of extension of the TAR by deposition from the tapered end. The new observations generally support a reversing transverse dune origin for TARs with heights ≥ 1 m, and a granule ripple origin for TAR-like ripples with heights ≤ 0.5 m.