Seasonal TES and MOC observations of the Rusell Crater dune field: recent surface runoff on a dune slope within the last Martian year ?

Kurzfassung

Rill erosion on a dune slope in the Russell Crater dune field was detected on the high resolution Mars Orbiter Camera (MOC)-NA image M1901170 at 54.5°S and 347.3°W. Identical erosion features occur on dunes in the Green Crater at 53.0°S and 8.2°W. The identified erosional morphology differs from previously observed gully erosion elsewhere on Mars. Seasonal observations indicate that the extremely fresh appearing erosion might be caused by recent surface runoff within the last Martian year. The erosional features in the Russell Crater dune field are located on a 350 m high dune slope with a dip of about 8°. The erosion starts in small alcoves in a dendritic pattern at the dune crest and merges after a short distance into main channels, which have a parallel pattern following the slope topography. In contrast to all other observed gullies on Mars they run out and abruptly end at the dune base without a depositional apron. The morphological forms show strong affinity to rill erosion on Earth, except from the lack of an apron. The morphology of the rills indicates that overland flow caused the erosion. The image was acquired in mid autumn at LS 50°. The very fresh appearing rills suggest that the erosion took place by a defrosting process between late winter and mid spring indicated by seasonal observations of TES albedo and temperature data. The temperature increases from 148°K in winter up to an observed maximum temperature of 276°K (near the water ice sublimation temperature) in mid spring. In the same time period the albedo decreases from 0.3 to 0.1. We favour an erosion process by liquid water: the rills are located in absolute elevations of about 200 m and the retreat of the south polar cap leads to an increase of the atmospheric pressure in the southern spring which could allow liquid water to be stable in this region. The lack of a depositional apron may be caused by compaction of the dust material with potentially simultaneous sublimation of the fluid.